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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
  <body>
    <h1>Domain XML format</h1>

    <ul id="toc"></ul>

    <p>
      This section describes the XML format used to represent domains, there are
      variations on the format based on the kind of domains run and the options
      used to launch them. For hypervisor specific details consult the
      <a href="drivers.html">driver docs</a>
    </p>


    <h2><a id="elements">Element and attribute overview</a></h2>

    <p>
      The root element required for all virtual machines is
      named <code>domain</code>. It has two attributes, the
      <a id="attributeDomainType"><code>type</code></a>
      specifies the hypervisor used for running
      the domain. The allowed values are driver specific, but
      include "xen", "kvm", "qemu" and "lxc". The
      second attribute is <code>id</code> which is a unique
      integer identifier for the running guest machine. Inactive
      machines have no id value.
    </p>


    <h3><a id="elementsMetadata">General metadata</a></h3>

<pre>
&lt;domain type='kvm' id='1'&gt;
  &lt;name&gt;MyGuest&lt;/name&gt;
  &lt;uuid&gt;4dea22b3-1d52-d8f3-2516-782e98ab3fa0&lt;/uuid&gt;
  &lt;genid&gt;43dc0cf8-809b-4adb-9bea-a9abb5f3d90e&lt;/genid&gt;
  &lt;title&gt;A short description - title - of the domain&lt;/title&gt;
  &lt;description&gt;Some human readable description&lt;/description&gt;
  &lt;metadata&gt;
    &lt;app1:foo xmlns:app1="http://app1.org/app1/"&gt;..&lt;/app1:foo&gt;
    &lt;app2:bar xmlns:app2="http://app1.org/app2/"&gt;..&lt;/app2:bar&gt;
  &lt;/metadata&gt;
  ...</pre>

    <dl>
      <dt><code>name</code></dt>
      <dd>The content of the <code>name</code> element provides
        a short name for the virtual machine. This name should
        consist only of alpha-numeric characters and is required
        to be unique within the scope of a single host. It is
        often used to form the filename for storing the persistent
        configuration file. <span class="since">Since 0.0.1</span></dd>
      <dt><code>uuid</code></dt>
      <dd>The content of the <code>uuid</code> element provides
        a globally unique identifier for the virtual machine.
        The format must be RFC 4122 compliant,
        eg <code>3e3fce45-4f53-4fa7-bb32-11f34168b82b</code>.
        If omitted when defining/creating a new machine, a random
        UUID is generated. It is also possible to provide the UUID
        via a <a href="#elementsSysinfo"><code>sysinfo</code></a>
        specification. <span class="since">Since 0.0.1, sysinfo
        since 0.8.7</span></dd>

      <dt><code>genid</code></dt>
      <dd><span class="since">Since 4.4.0</span>, the <code>genid</code>
        element can be used to add a Virtual Machine Generation ID which
        exposes a 128-bit, cryptographically random, integer value identifier,
        referred to as a Globally Unique Identifier (GUID) using the same
        format as the <code>uuid</code>. The value is used to help notify
        the guest operating system when the virtual machine is re-executing
        something that has already executed before, such as:

        <ul>
          <li>VM starts executing a snapshot</li>
          <li>VM is recovered from backup</li>
          <li>VM is failover in a disaster recovery environment</li>
          <li>VM is imported, copied, or cloned</li>
        </ul>

        The guest operating system notices the change and is then able to
        react as appropriate by marking its copies of distributed databases
        as dirty, re-initializing its random number generator, etc.

        <p>
        The libvirt XML parser will accept both a provided GUID value
        or just &lt;genid/&gt; in which case a GUID will be generated
        and saved in the XML. For the transitions such as above, libvirt
        will change the GUID before re-executing.</p></dd>

      <dt><code>title</code></dt>
      <dd>The optional element <code>title</code> provides space for a
        short description of the domain. The title should not contain
        any newlines. <span class="since">Since 0.9.10</span>.</dd>

      <dt><code>description</code></dt>
      <dd>The content of the <code>description</code> element provides a
        human readable description of the virtual machine. This data is not
        used by libvirt in any way, it can contain any information the user
        wants. <span class="since">Since 0.7.2</span></dd>

      <dt><code>metadata</code></dt>
      <dd>The <code>metadata</code> node can be used by applications
        to store custom metadata in the form of XML
        nodes/trees. Applications must use custom namespaces on their
        XML nodes/trees, with only one top-level element per namespace
        (if the application needs structure, they should have
        sub-elements to their namespace
        element). <span class="since">Since 0.9.10</span></dd>
   </dl>

    <h3><a id="elementsOS">Operating system booting</a></h3>

    <p>
      There are a number of different ways to boot virtual machines
      each with their own pros and cons.
    </p>

    <h4><a id="elementsOSBIOS">BIOS bootloader</a></h4>

    <p>
      Booting via the BIOS is available for hypervisors supporting
      full virtualization. In this case the BIOS has a boot order
      priority (floppy, harddisk, cdrom, network) determining where
      to obtain/find the boot image.
    </p>

<pre>
...
&lt;os firmware='efi'&gt;
  &lt;type&gt;hvm&lt;/type&gt;
  &lt;loader readonly='yes' secure='no' type='rom'&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
  &lt;nvram template='/usr/share/OVMF/OVMF_VARS.fd'&gt;/var/lib/libvirt/nvram/guest_VARS.fd&lt;/nvram&gt;
  &lt;boot dev='hd'/&gt;
  &lt;boot dev='cdrom'/&gt;
  &lt;bootmenu enable='yes' timeout='3000'/&gt;
  &lt;smbios mode='sysinfo'/&gt;
  &lt;bios useserial='yes' rebootTimeout='0'/&gt;
&lt;/os&gt;
...</pre>

    <dl>
      <dt><code>firmware</code></dt>
      <dd>The <code>firmware</code> attribute allows management
        applications to automatically fill <code>&lt;loader/&gt;</code>
        and <code>&lt;nvram/&gt;</code> elements and possibly enable
        some features required by selected firmware. Accepted values are
        <code>bios</code> and <code>efi</code>.<br/>
        The selection process scans for files describing installed
        firmware images in specified location and uses the most specific
        one which fulfils domain requirements. The locations in order of
        preference (from generic to most specific one) are:
        <ul>
          <li><code>/usr/share/qemu/firmware</code></li>
          <li><code>/etc/qemu/firmware</code></li>
          <li><code>$XDG_CONFIG_HOME/qemu/firmware</code></li>
        </ul>
        For more information refer to firmware metadata specification as
        described in <code>docs/interop/firmware.json</code> in QEMU
        repository. Regular users do not need to bother.
        <span class="since">Since 5.2.0 (QEMU and KVM only)</span><br/>
        For VMware guests, this is set to <code>efi</code> when the guest
        uses UEFI, and it is not set when using BIOS.
        <span class="since">Since 5.3.0 (VMware ESX and Workstation/Player)</span>
      </dd>
      <dt><code>type</code></dt>
      <dd>The content of the <code>type</code> element specifies the
        type of operating system to be booted in the virtual machine.
        <code>hvm</code> indicates that the OS is one designed to run
        on bare metal, so requires full virtualization. <code>linux</code>
        (badly named!) refers to an OS that supports the Xen 3 hypervisor
        guest ABI. There are also two optional attributes, <code>arch</code>
        specifying the CPU architecture to virtualization,
        and <a id="attributeOSTypeMachine"><code>machine</code></a> referring
        to the machine type. The <a href="formatcaps.html">Capabilities XML</a>
        provides details on allowed values for
        these. <span class="since">Since 0.0.1</span></dd>
      <dt><a id="elementLoader"><code>loader</code></a></dt>
      <dd>The optional <code>loader</code> tag refers to a firmware blob,
        which is specified by absolute path,
        used to assist the domain creation process. It is used by Xen
        fully virtualized domains as well as setting the QEMU BIOS file
        path for QEMU/KVM domains. <span class="since">Xen since 0.1.0,
        QEMU/KVM since 0.9.12</span> Then, <span class="since">since
        1.2.8</span> it's possible for the element to have two
        optional attributes: <code>readonly</code> (accepted values are
        <code>yes</code> and <code>no</code>) to reflect the fact that the
        image should be writable or read-only. The second attribute
        <code>type</code> accepts values <code>rom</code> and
        <code>pflash</code>. It tells the hypervisor where in the guest
        memory the file should be mapped.  For instance, if the loader
        path points to an UEFI image, <code>type</code> should be
        <code>pflash</code>. Moreover, some firmwares may
        implement the Secure boot feature. Attribute
        <code>secure</code> can be used then to control it.
        <span class="since">Since 2.1.0</span></dd>
      <dt><code>nvram</code></dt>
      <dd>Some UEFI firmwares may want to use a non-volatile memory to store
        some variables. In the host, this is represented as a file and the
        absolute path to the file is stored in this element. Moreover, when the
        domain is started up libvirt copies so called master NVRAM store file
        defined in <code>qemu.conf</code>. If needed, the <code>template</code>
        attribute can be used to per domain override map of master NVRAM stores
        from the config file. Note, that for transient domains if the NVRAM file
        has been created by libvirt it is left behind and it is management
        application's responsibility to save and remove file (if needed to be
        persistent). <span class="since">Since 1.2.8</span></dd>
      <dt><code>boot</code></dt>
      <dd>The <code>dev</code> attribute takes one of the values "fd", "hd",
        "cdrom" or "network" and is used to specify the next boot device
        to consider. The <code>boot</code> element can be repeated multiple
        times to setup a priority list of boot devices to try in turn.
        Multiple devices of the same type are sorted according to their
        targets while preserving the order of buses. After defining the
        domain, its XML configuration returned by libvirt (through
        virDomainGetXMLDesc) lists devices in the sorted order. Once sorted,
        the first device is marked as bootable. Thus, e.g., a domain
        configured to boot from "hd" with vdb, hda, vda, and hdc disks
        assigned to it will boot from vda (the sorted list is vda, vdb, hda,
        hdc). Similar domain with hdc, vda, vdb, and hda disks will boot from
        hda (sorted disks are: hda, hdc, vda, vdb). It can be tricky to
        configure in the desired way, which is why per-device boot elements
        (see <a href="#elementsDisks">disks</a>,
        <a href="#elementsNICS">network interfaces</a>, and
        <a href="#elementsHostDev">USB and PCI devices</a> sections below) were
        introduced and they are the preferred way providing full control over
        booting order. The <code>boot</code> element and per-device boot
        elements are mutually exclusive. <span class="since">Since 0.1.3,
        per-device boot since 0.8.8</span>
      </dd>
      <dt><code>smbios</code></dt>
      <dd>How to populate SMBIOS information visible in the guest.
        The <code>mode</code> attribute must be specified, and is either
        "emulate" (let the hypervisor generate all values), "host" (copy
        all of Block 0 and Block 1, except for the UUID, from the host's
        SMBIOS values;
        the <a href="html/libvirt-libvirt-host.html#virConnectGetSysinfo">
        <code>virConnectGetSysinfo</code></a> call can be
        used to see what values are copied), or "sysinfo" (use the values in
        the <a href="#elementsSysinfo">sysinfo</a> element).  If not
        specified, the hypervisor default is used. <span class="since">
        Since 0.8.7</span>
      </dd>
  </dl>
      <p>Up till here the BIOS/UEFI configuration knobs are generic enough to
      be implemented by majority (if not all) firmwares out there. However,
      from now on not every single setting makes sense to all firmwares. For
      instance, <code>rebootTimeout</code> doesn't make sense for UEFI,
      <code>useserial</code> might not be usable with a BIOS firmware that
      doesn't produce any output onto serial line, etc. Moreover, firmwares
      don't usually export their capabilities for libvirt (or users) to check.
      And the set of their capabilities can change with every new release.
      Hence users are advised to try the settings they use before relying on
      them in production.</p>
  <dl>
      <dt><code>bootmenu</code></dt>
      <dd> Whether or not to enable an interactive boot menu prompt on guest
      startup. The <code>enable</code> attribute can be either "yes" or "no".
      If not specified, the hypervisor default is used. <span class="since">
      Since 0.8.3</span>
      Additional attribute <code>timeout</code> takes the number of milliseconds
      the boot menu should wait until it times out.  Allowed values are numbers
      in range [0, 65535] inclusive and it is ignored unless <code>enable</code>
      is set to "yes". <span class="since">Since 1.2.8</span>
      </dd>
      <dt><code>bios</code></dt>
      <dd>This element has attribute <code>useserial</code> with possible
        values <code>yes</code> or <code>no</code>. It enables or disables
        Serial Graphics Adapter which allows users to see BIOS messages
        on a serial port. Therefore, one needs to have
        <a href="#elementCharSerial">serial port</a> defined.
        <span class="since">Since 0.9.4</span>.
        <span class="since">Since 0.10.2 (QEMU only)</span> there is
        another attribute, <code>rebootTimeout</code> that controls
        whether and after how long the guest should start booting
        again in case the boot fails (according to BIOS). The value is
        in milliseconds with maximum of <code>65535</code> and special
        value <code>-1</code> disables the reboot.
      </dd>
    </dl>

    <h4><a id="elementsOSBootloader">Host bootloader</a></h4>

    <p>
      Hypervisors employing paravirtualization do not usually emulate
      a BIOS, and instead the host is responsible to kicking off the
      operating system boot. This may use a pseudo-bootloader in the
      host to provide an interface to choose a kernel for the guest.
      An example is <code>pygrub</code> with Xen. The Bhyve hypervisor
      also uses a host bootloader, either <code>bhyveload</code> or
      <code>grub-bhyve</code>.
    </p>

<pre>
...
&lt;bootloader&gt;/usr/bin/pygrub&lt;/bootloader&gt;
&lt;bootloader_args&gt;--append single&lt;/bootloader_args&gt;
...</pre>

    <dl>
      <dt><code>bootloader</code></dt>
      <dd>The content of the <code>bootloader</code> element provides
        a fully qualified path to the bootloader executable in the
        host OS. This bootloader will be run to choose which kernel
        to boot. The required output of the bootloader is dependent
        on the hypervisor in use. <span class="since">Since 0.1.0</span></dd>
      <dt><code>bootloader_args</code></dt>
      <dd>The optional <code>bootloader_args</code> element allows
        command line arguments to be passed to the bootloader.
        <span class="since">Since 0.2.3</span>
        </dd>

    </dl>

    <h4><a id="elementsOSKernel">Direct kernel boot</a></h4>

    <p>
      When installing a new guest OS it is often useful to boot directly
      from a kernel and initrd stored in the host OS, allowing command
      line arguments to be passed directly to the installer. This capability
      is usually available for both para and full virtualized guests.
    </p>

<pre>
...
&lt;os&gt;
  &lt;type&gt;hvm&lt;/type&gt;
  &lt;loader&gt;/usr/lib/xen/boot/hvmloader&lt;/loader&gt;
  &lt;kernel&gt;/root/f8-i386-vmlinuz&lt;/kernel&gt;
  &lt;initrd&gt;/root/f8-i386-initrd&lt;/initrd&gt;
  &lt;cmdline&gt;console=ttyS0 ks=http://example.com/f8-i386/os/&lt;/cmdline&gt;
  &lt;dtb&gt;/root/ppc.dtb&lt;/dtb&gt;
  &lt;acpi&gt;
    &lt;table type='slic'&gt;/path/to/slic.dat&lt;/table&gt;
  &lt;/acpi&gt;
&lt;/os&gt;
...</pre>

    <dl>
      <dt><code>type</code></dt>
      <dd>This element has the same semantics as described earlier in the
        <a href="#elementsOSBIOS">BIOS boot section</a></dd>
      <dt><code>loader</code></dt>
      <dd>This element has the same semantics as described earlier in the
        <a href="#elementsOSBIOS">BIOS boot section</a></dd>
      <dt><code>kernel</code></dt>
      <dd>The contents of this element specify the fully-qualified path
        to the kernel image in the host OS.</dd>
      <dt><code>initrd</code></dt>
      <dd>The contents of this element specify the fully-qualified path
        to the (optional) ramdisk image in the host OS.</dd>
      <dt><code>cmdline</code></dt>
      <dd>The contents of this element specify arguments to be passed to
        the kernel (or installer) at boot time. This is often used to
        specify an alternate primary console (eg serial port), or the
        installation media source / kickstart file</dd>
      <dt><code>dtb</code></dt>
      <dd>The contents of this element specify the fully-qualified path
        to the (optional) device tree binary (dtb) image in the host OS.
        <span class="since">Since 1.0.4</span></dd>
      <dt><code>acpi</code></dt>
      <dd>The <code>table</code> element contains a fully-qualified path
        to the ACPI table. The <code>type</code> attribute contains the
        ACPI table type (currently only <code>slic</code> is supported)
        <span class="since">Since 1.3.5 (QEMU only)</span></dd>
    </dl>

    <h4><a id="elementsOSContainer">Container boot</a></h4>

    <p>
      When booting a domain using container based virtualization, instead
      of a kernel / boot image, a path to the init binary is required, using
      the <code>init</code> element. By default this will be launched with
      no arguments. To specify the initial argv, use the <code>initarg</code>
      element, repeated as many time as is required. The <code>cmdline</code>
      element, if set will be used to provide an equivalent to <code>/proc/cmdline</code>
      but will not affect init argv.
    </p>
    <p>
      To set environment variables, use the <code>initenv</code> element, one
      for each variable.
    </p>
    <p>
      To set a custom work directory for the init, use the <code>initdir</code>
      element.
    </p>
    <p>
      To run the init command as a given user or group, use the <code>inituser</code>
      or <code>initgroup</code> elements respectively. Both elements can be provided
      either a user (resp. group) id or a name. Prefixing the user or group id with
      a <code>+</code> will force it to be considered like a numeric value. Without
      this, it will be first tried as a user or group name.
    </p>

    <pre>
&lt;os&gt;
  &lt;type arch='x86_64'&gt;exe&lt;/type&gt;
  &lt;init&gt;/bin/systemd&lt;/init&gt;
  &lt;initarg&gt;--unit&lt;/initarg&gt;
  &lt;initarg&gt;emergency.service&lt;/initarg&gt;
  &lt;initenv name='MYENV'&gt;some value&lt;/initenv&gt;
  &lt;initdir&gt;/my/custom/cwd&lt;/initdir&gt;
  &lt;inituser&gt;tester&lt;/inituser&gt;
  &lt;initgroup&gt;1000&lt;/initgroup&gt;
&lt;/os&gt;
    </pre>


    <p>
      If you want to enable user namespace, set the <code>idmap</code> element.
      The <code>uid</code> and <code>gid</code> elements have three attributes:
    </p>

    <dl>
      <dt><code>start</code></dt>
      <dd>First user ID in container. It must be '0'.</dd>
      <dt><code>target</code></dt>
      <dd>The first user ID in container will be mapped to this target user
          ID in host.</dd>
      <dt><code>count</code></dt>
      <dd>How many users in container are allowed to map to host's user.</dd>
    </dl>

    <pre>
&lt;idmap&gt;
  &lt;uid start='0' target='1000' count='10'/&gt;
  &lt;gid start='0' target='1000' count='10'/&gt;
&lt;/idmap&gt;
    </pre>


    <h3><a id="elementsSysinfo">SMBIOS System Information</a></h3>

    <p>
      Some hypervisors allow control over what system information is
      presented to the guest (for example, SMBIOS fields can be
      populated by a hypervisor and inspected via
      the <code>dmidecode</code> command in the guest).  The
      optional <code>sysinfo</code> element covers all such categories
      of information. <span class="since">Since 0.8.7</span>
    </p>

<pre>
...
&lt;os&gt;
  &lt;smbios mode='sysinfo'/&gt;
  ...
&lt;/os&gt;
&lt;sysinfo type='smbios'&gt;
  &lt;bios&gt;
    &lt;entry name='vendor'&gt;LENOVO&lt;/entry&gt;
  &lt;/bios&gt;
  &lt;system&gt;
    &lt;entry name='manufacturer'&gt;Fedora&lt;/entry&gt;
    &lt;entry name='product'&gt;Virt-Manager&lt;/entry&gt;
    &lt;entry name='version'&gt;0.9.4&lt;/entry&gt;
  &lt;/system&gt;
  &lt;baseBoard&gt;
    &lt;entry name='manufacturer'&gt;LENOVO&lt;/entry&gt;
    &lt;entry name='product'&gt;20BE0061MC&lt;/entry&gt;
    &lt;entry name='version'&gt;0B98401 Pro&lt;/entry&gt;
    &lt;entry name='serial'&gt;W1KS427111E&lt;/entry&gt;
  &lt;/baseBoard&gt;
  &lt;chassis&gt;
    &lt;entry name='manufacturer'&gt;Dell Inc.&lt;/entry&gt;
    &lt;entry name='version'&gt;2.12&lt;/entry&gt;
    &lt;entry name='serial'&gt;65X0XF2&lt;/entry&gt;
    &lt;entry name='asset'&gt;40000101&lt;/entry&gt;
    &lt;entry name='sku'&gt;Type3Sku1&lt;/entry&gt;
  &lt;/chassis&gt;
  &lt;oemStrings&gt;
    &lt;entry&gt;myappname:some arbitrary data&lt;/entry&gt;
    &lt;entry&gt;otherappname:more arbitrary data&lt;/entry&gt;
  &lt;/oemStrings&gt;
&lt;/sysinfo&gt;
...</pre>

    <p>
      The <code>sysinfo</code> element has a mandatory
      attribute <code>type</code> that determine the layout of
      sub-elements, with supported values of:
    </p>

    <dl>
      <dt><code>smbios</code></dt>
      <dd>Sub-elements call out specific SMBIOS values, which will
      affect the guest if used in conjunction with
      the <code>smbios</code> sub-element of
      the <a href="#elementsOS"><code>os</code></a> element.  Each
      sub-element of <code>sysinfo</code> names a SMBIOS block, and
      within those elements can be a list of <code>entry</code>
      elements that describe a field within the block.  The following
      blocks and entries are recognized:
        <dl>
          <dt><code>bios</code></dt>
          <dd>
            This is block 0 of SMBIOS, with entry names drawn from:
            <dl>
               <dt><code>vendor</code></dt>
               <dd>BIOS Vendor's Name</dd>
               <dt><code>version</code></dt>
               <dd>BIOS Version</dd>
               <dt><code>date</code></dt>
               <dd>BIOS release date. If supplied, is in either mm/dd/yy or
                   mm/dd/yyyy format. If the year portion of the string is
                   two digits, the year is assumed to be 19yy.</dd>
               <dt><code>release</code></dt>
               <dd>System BIOS Major and Minor release number values
                   concatenated together as one string separated by
                   a period, for example, 10.22.</dd>
           </dl>
          </dd>
          <dt><code>system</code></dt>
          <dd>
            This is block 1 of SMBIOS, with entry names drawn from:
            <dl>
                <dt><code>manufacturer</code></dt>
                <dd>Manufacturer of BIOS</dd>
                <dt><code>product</code></dt>
                <dd>Product Name</dd>
                <dt><code>version</code></dt>
                <dd>Version of the product</dd>
                <dt><code>serial</code></dt>
                <dd>Serial number</dd>
                <dt><code>uuid</code></dt>
                <dd>Universal Unique ID number. If this entry is provided
                alongside a top-level
                <a href="#elementsMetadata"><code>uuid</code></a> element,
                then the two values must match.</dd>
                <dt><code>sku</code></dt>
                <dd>SKU number to identify a particular configuration.</dd>
                <dt><code>family</code></dt>
                <dd>Identify the family a particular computer belongs to.</dd>
            </dl>
          </dd>
          <dt><code>baseBoard</code></dt>
          <dd>
            This is block 2 of SMBIOS. This element can be repeated multiple
            times to describe all the base boards; however, not all
            hypervisors necessarily support the repetition. The element can
            have the following children:
            <dl>
                <dt><code>manufacturer</code></dt>
                <dd>Manufacturer of BIOS</dd>
                <dt><code>product</code></dt>
                <dd>Product Name</dd>
                <dt><code>version</code></dt>
                <dd>Version of the product</dd>
                <dt><code>serial</code></dt>
                <dd>Serial number</dd>
                <dt><code>asset</code></dt>
                <dd>Asset tag</dd>
                <dt><code>location</code></dt>
                <dd>Location in chassis</dd>
            </dl>
            NB: Incorrectly supplied entries for the
            <code>bios</code>, <code>system</code> or <code>baseBoard</code>
            blocks will be ignored without error.  Other than <code>uuid</code>
            validation and <code>date</code> format checking, all values are
            passed as strings to the hypervisor driver.
          </dd>
          <dt><code>chassis</code></dt>
          <dd>
            <span class="since">Since 4.1.0,</span> this is block 3 of
            SMBIOS, with entry names drawn from:
            <dl>
                <dt><code>manufacturer</code></dt>
                <dd>Manufacturer of Chassis</dd>
                <dt><code>version</code></dt>
                <dd>Version of the Chassis</dd>
                <dt><code>serial</code></dt>
                <dd>Serial number</dd>
                <dt><code>asset</code></dt>
                <dd>Asset tag</dd>
                <dt><code>sku</code></dt>
                <dd>SKU number</dd>
            </dl>
          </dd>
          <dt><code>oemStrings</code></dt>
          <dd>
            This is block 11 of SMBIOS. This element should appear once and
            can have multiple <code>entry</code> child elements, each providing
            arbitrary string data. There are no restrictions on what data can
            be provided in the entries, however, if the data is intended to be
            consumed by an application in the guest, it is recommended to use
            the application name as a prefix in the string. (<span class="since">Since 4.1.0</span>)
          </dd>
        </dl>
      </dd>
    </dl>

    <h3><a id="elementsCPUAllocation">CPU Allocation</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;vcpu placement='static' cpuset="1-4,^3,6" current="1"&gt;2&lt;/vcpu&gt;
  &lt;vcpus&gt;
    &lt;vcpu id='0' enabled='yes' hotpluggable='no' order='1'/&gt;
    &lt;vcpu id='1' enabled='no' hotpluggable='yes'/&gt;
  &lt;/vcpus&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>vcpu</code></dt>
      <dd>The content of this element defines the maximum number of virtual
        CPUs allocated for the guest OS, which must be between 1 and
        the maximum supported by the hypervisor.
        <dl>
         <dt><code>cpuset</code></dt>
         <dd>
           The optional attribute <code>cpuset</code> is a comma-separated
           list of physical CPU numbers that domain process and virtual CPUs
           can be pinned to by default. (NB: The pinning policy of domain
           process and virtual CPUs can be specified separately by
           <code>cputune</code>. If the attribute <code>emulatorpin</code>
           of <code>cputune</code> is specified, the <code>cpuset</code>
           specified by <code>vcpu</code> here will be ignored. Similarly,
           for virtual CPUs which have the <code>vcpupin</code> specified,
           the <code>cpuset</code> specified by <code>cpuset</code> here
           will be ignored. For virtual CPUs which don't have
           <code>vcpupin</code> specified, each will be pinned to the physical
           CPUs specified by <code>cpuset</code> here).
           Each element in that list is either a single CPU number,
           a range of CPU numbers, or a caret followed by a CPU number to
           be excluded from a previous range.
           <span class="since">Since 0.4.4</span>
         </dd>
         <dt><code>current</code></dt>
         <dd>
           The optional attribute <code>current</code> can
           be used to specify whether fewer than the maximum number of
           virtual CPUs should be enabled.
           <span class="since">Since 0.8.5</span>
         </dd>
         <dt><code>placement</code></dt>
         <dd>
           The optional attribute <code>placement</code> can be used to
           indicate the CPU placement mode for domain process. The value can
           be either "static" or "auto", but defaults to <code>placement</code>
           of <code>numatune</code> or "static" if <code>cpuset</code> is
           specified. Using "auto" indicates the domain process will be pinned
           to the advisory nodeset from querying numad and the value of
           attribute <code>cpuset</code> will be ignored if it's specified.
           If both <code>cpuset</code> and <code>placement</code> are not
           specified or if <code>placement</code> is "static", but no
           <code>cpuset</code> is specified, the domain process will be
           pinned to all the available physical CPUs.
           <span class="since">Since 0.9.11 (QEMU and KVM only)</span>
         </dd>
        </dl>
      </dd>
      <dt><code>vcpus</code></dt>
      <dd>
        The vcpus element allows to control state of individual vCPUs.

        The <code>id</code> attribute specifies the vCPU id as used by libvirt
        in other places such as vCPU pinning, scheduler information and NUMA
        assignment. Note that the vCPU ID as seen in the guest may differ from
        libvirt ID in certain cases. Valid IDs are from 0 to the maximum vCPU
        count as set by the <code>vcpu</code> element minus 1.

        The <code>enabled</code> attribute allows to control the state of the
        vCPU. Valid values are <code>yes</code> and <code>no</code>.

        <code>hotpluggable</code> controls whether given vCPU can be hotplugged
        and hotunplugged in cases when the CPU is enabled at boot. Note that
        all disabled vCPUs must be hotpluggable. Valid values are
        <code>yes</code> and <code>no</code>.

        <code>order</code> allows to specify the order to add the online vCPUs.
        For hypervisors/platforms that require to insert multiple vCPUs at once
        the order may be duplicated across all vCPUs that need to be
        enabled at once. Specifying order is not necessary, vCPUs are then
        added in an arbitrary order. If order info is used, it must be used for
        all online vCPUs. Hypervisors may clear or update ordering information
        during certain operations to assure valid configuration.

        Note that hypervisors may create hotpluggable vCPUs differently from
        boot vCPUs thus special initialization may be necessary.

        Hypervisors may require that vCPUs enabled on boot which are not
        hotpluggable are clustered at the beginning starting with ID 0. It may
        be also required that vCPU 0 is always present and non-hotpluggable.

        Note that providing state for individual CPUs may be necessary to enable
        support of addressable vCPU hotplug and this feature may not be
        supported by all hypervisors.

        For QEMU the following conditions are required. vCPU 0 needs to be
        enabled and non-hotpluggable. On PPC64 along with it vCPUs that are in
        the same core need to be enabled as well. All non-hotpluggable CPUs
        present at boot need to be grouped after vCPU 0.
        <span class="since">Since 2.2.0 (QEMU only)</span>
      </dd>
    </dl>

    <h3><a id="elementsIOThreadsAllocation">IOThreads Allocation</a></h3>
      <p>
        IOThreads are dedicated event loop threads for supported disk
        devices to perform block I/O requests in order to improve
        scalability especially on an SMP host/guest with many LUNs.
        <span class="since">Since 1.2.8 (QEMU only)</span>
      </p>

<pre>
&lt;domain&gt;
  ...
  &lt;iothreads&gt;4&lt;/iothreads&gt;
  ...
&lt;/domain&gt;
</pre>
<pre>
&lt;domain&gt;
  ...
  &lt;iothreadids&gt;
    &lt;iothread id="2"/&gt;
    &lt;iothread id="4"/&gt;
    &lt;iothread id="6"/&gt;
    &lt;iothread id="8"/&gt;
  &lt;/iothreadids&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>iothreads</code></dt>
      <dd>
        The content of this optional element defines the number
        of IOThreads to be assigned to the domain for use by
        supported target storage devices. There
        should be only 1 or 2 IOThreads per host CPU. There may be more
        than one supported device assigned to each IOThread.
        <span class="since">Since 1.2.8</span>
      </dd>
      <dt><code>iothreadids</code></dt>
      <dd>
        The optional <code>iothreadids</code> element provides the capability
        to specifically define the IOThread ID's for the domain.  By default,
        IOThread ID's are sequentially numbered starting from 1 through the
        number of <code>iothreads</code> defined for the domain. The
        <code>id</code> attribute is used to define the IOThread ID. The
        <code>id</code> attribute must be a positive integer greater than 0.
        If there are less <code>iothreadids</code> defined than
        <code>iothreads</code> defined for the domain, then libvirt will
        sequentially fill <code>iothreadids</code> starting at 1 avoiding
        any predefined <code>id</code>. If there are more
        <code>iothreadids</code> defined than <code>iothreads</code>
        defined for the domain, then the <code>iothreads</code> value
        will be adjusted accordingly.
        <span class="since">Since 1.2.15</span>
       </dd>
    </dl>

    <h3><a id="elementsCPUTuning">CPU Tuning</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;cputune&gt;
    &lt;vcpupin vcpu="0" cpuset="1-4,^2"/&gt;
    &lt;vcpupin vcpu="1" cpuset="0,1"/&gt;
    &lt;vcpupin vcpu="2" cpuset="2,3"/&gt;
    &lt;vcpupin vcpu="3" cpuset="0,4"/&gt;
    &lt;emulatorpin cpuset="1-3"/&gt;
    &lt;iothreadpin iothread="1" cpuset="5,6"/&gt;
    &lt;iothreadpin iothread="2" cpuset="7,8"/&gt;
    &lt;shares&gt;2048&lt;/shares&gt;
    &lt;period&gt;1000000&lt;/period&gt;
    &lt;quota&gt;-1&lt;/quota&gt;
    &lt;global_period&gt;1000000&lt;/global_period&gt;
    &lt;global_quota&gt;-1&lt;/global_quota&gt;
    &lt;emulator_period&gt;1000000&lt;/emulator_period&gt;
    &lt;emulator_quota&gt;-1&lt;/emulator_quota&gt;
    &lt;iothread_period&gt;1000000&lt;/iothread_period&gt;
    &lt;iothread_quota&gt;-1&lt;/iothread_quota&gt;
    &lt;vcpusched vcpus='0-4,^3' scheduler='fifo' priority='1'/&gt;
    &lt;iothreadsched iothreads='2' scheduler='batch'/&gt;
    &lt;cachetune vcpus='0-3'&gt;
      &lt;cache id='0' level='3' type='both' size='3' unit='MiB'/&gt;
      &lt;cache id='1' level='3' type='both' size='3' unit='MiB'/&gt;
      &lt;monitor level='3' vcpus='1'/&gt;
      &lt;monitor level='3' vcpus='0-3'/&gt;
    &lt;/cachetune&gt;
    &lt;cachetune vcpus='4-5'&gt;
      &lt;monitor level='3' vcpus='4'/&gt;
      &lt;monitor level='3' vcpus='5'/&gt;
    &lt;/cachetune&gt;
    &lt;memorytune vcpus='0-3'&gt;
      &lt;node id='0' bandwidth='60'/&gt;
    &lt;/memorytune&gt;

  &lt;/cputune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>cputune</code></dt>
      <dd>
         The optional <code>cputune</code> element provides details
         regarding the CPU tunable parameters for the domain.
         <span class="since">Since 0.9.0</span>
      </dd>
      <dt><code>vcpupin</code></dt>
      <dd>
        The optional <code>vcpupin</code> element specifies which of host's
        physical CPUs the domain vCPU will be pinned to. If this is omitted,
        and attribute <code>cpuset</code> of element <code>vcpu</code> is
        not specified, the vCPU is pinned to all the physical CPUs by default.
        It contains two required attributes, the attribute <code>vcpu</code>
        specifies vCPU id, and the attribute <code>cpuset</code> is same as
        attribute <code>cpuset</code> of element <code>vcpu</code>.
        (NB: Only qemu driver support)
        <span class="since">Since 0.9.0</span>
       </dd>
       <dt><code>emulatorpin</code></dt>
       <dd>
         The optional <code>emulatorpin</code> element specifies which of host
         physical CPUs the "emulator", a subset of a domain not including vCPU
         or iothreads will be pinned to. If this is omitted, and attribute
         <code>cpuset</code> of element <code>vcpu</code> is not specified,
         "emulator" is pinned to all the physical CPUs by default. It contains
         one required attribute <code>cpuset</code> specifying which physical
         CPUs to pin to.
       </dd>
       <dt><code>iothreadpin</code></dt>
       <dd>
         The optional <code>iothreadpin</code> element specifies which of host
         physical CPUs the IOThreads will be pinned to. If this is omitted
         and attribute <code>cpuset</code> of element <code>vcpu</code> is
         not specified, the IOThreads are pinned to all the physical CPUs
         by default. There are two required attributes, the attribute
         <code>iothread</code> specifies the IOThread ID and the attribute
         <code>cpuset</code> specifying which physical CPUs to pin to. See
         the <code>iothreadids</code>
         <a href="#elementsIOThreadsAllocation"><code>description</code></a>
         for valid <code>iothread</code> values.
        <span class="since">Since 1.2.9</span>
       </dd>
      <dt><code>shares</code></dt>
      <dd>
        The optional <code>shares</code> element specifies the proportional
        weighted share for the domain. If this is omitted, it defaults to
        the OS provided defaults. NB, There is no unit for the value,
        it's a relative measure based on the setting of other VM,
        e.g. A VM configured with value
        2048 will get twice as much CPU time as a VM configured with value 1024.
        <span class="since">Since 0.9.0</span>
      </dd>
      <dt><code>period</code></dt>
      <dd>
        The optional <code>period</code> element specifies the enforcement
        interval (unit: microseconds). Within <code>period</code>, each vCPU of
        the domain will not be allowed to consume more than <code>quota</code>
        worth of runtime. The value should be in range [1000, 1000000]. A period
        with value 0 means no value.
        <span class="since">Only QEMU driver support since 0.9.4, LXC since
        0.9.10</span>
      </dd>
      <dt><code>quota</code></dt>
      <dd>
        The optional <code>quota</code> element specifies the maximum allowed
        bandwidth (unit: microseconds). A domain with <code>quota</code> as any
        negative value indicates that the domain has infinite bandwidth for
        vCPU threads, which means that it is not bandwidth controlled. The value
        should be in range [1000, 18446744073709551] or less than 0. A quota
        with value 0 means no value. You can use this feature to ensure that all
        vCPUs run at the same speed.
        <span class="since">Only QEMU driver support since 0.9.4, LXC since
        0.9.10</span>
      </dd>
      <dt><code>global_period</code></dt>
      <dd>
        The optional <code>global_period</code> element specifies the
        enforcement CFS scheduler interval (unit: microseconds) for the whole
        domain in contrast with <code>period</code> which enforces the interval
        per vCPU. The value should be in range 1000, 1000000]. A
        <code>global_period</code> with value 0 means no value.
        <span class="since">Only QEMU driver support since 1.3.3</span>
      </dd>
      <dt><code>global_quota</code></dt>
      <dd>
        The optional <code>global_quota</code> element specifies the maximum
        allowed bandwidth (unit: microseconds) within a period for the whole
        domain. A domain with <code>global_quota</code> as any negative
        value indicates that the domain has infinite bandwidth, which means that
        it is not bandwidth controlled. The value should be in range
        [1000, 18446744073709551] or less than 0. A <code>global_quota</code>
        with value 0 means no value.
        <span class="since">Only QEMU driver support since 1.3.3</span>
      </dd>

      <dt><code>emulator_period</code></dt>
      <dd>
        The optional <code>emulator_period</code> element specifies the enforcement
        interval (unit: microseconds). Within <code>emulator_period</code>, emulator
        threads (those excluding vCPUs) of the domain will not be allowed to consume
        more than <code>emulator_quota</code> worth of runtime. The value should be
        in range [1000, 1000000]. A period with value 0 means no value.
        <span class="since">Only QEMU driver support since 0.10.0</span>
      </dd>
      <dt><code>emulator_quota</code></dt>
      <dd>
        The optional <code>emulator_quota</code> element specifies the maximum
        allowed bandwidth (unit: microseconds) for domain's emulator threads (those
        excluding vCPUs). A domain with <code>emulator_quota</code> as any negative
        value indicates that the domain has infinite bandwidth for emulator threads
        (those excluding vCPUs), which means that it is not bandwidth controlled.
        The value should be in range [1000, 18446744073709551] or less than 0. A
        quota with value 0 means no value.
        <span class="since">Only QEMU driver support since 0.10.0</span>
      </dd>

      <dt><code>iothread_period</code></dt>
      <dd>
        The optional <code>iothread_period</code> element specifies the
        enforcement interval (unit: microseconds) for IOThreads. Within
        <code>iothread_period</code>, each IOThread of the domain will
        not be allowed to consume more than <code>iothread_quota</code>
        worth of runtime. The value should be in range [1000, 1000000].
        An iothread_period with value 0 means no value.
        <span class="since">Only QEMU driver support since 2.1.0</span>
      </dd>
      <dt><code>iothread_quota</code></dt>
      <dd>
        The optional <code>iothread_quota</code> element specifies the maximum
        allowed bandwidth (unit: microseconds) for IOThreads. A domain with
        <code>iothread_quota</code> as any negative value indicates that the
        domain IOThreads have infinite bandwidth, which means that it is
        not bandwidth controlled. The value should be in range
        [1000, 18446744073709551] or less than 0. An <code>iothread_quota</code>
        with value 0 means no value. You can use this feature to ensure that
        all IOThreads run at the same speed.
        <span class="since">Only QEMU driver support since 2.1.0</span>
      </dd>

      <dt><code>vcpusched</code>, <code>iothreadsched</code>
      and <code>emulatorsched</code></dt>
      <dd>
        The optional
        <code>vcpusched</code>, <code>iothreadsched</code>
        and <code>emulatorsched</code> elements specify the scheduler type
        (values <code>batch</code>, <code>idle</code>, <code>fifo</code>,
        <code>rr</code>) for particular vCPU, IOThread and emulator threads
        respecively.  For <code>vcpusched</code> and <code>iothreadsched</code>
        the attributes <code>vcpus</code> and <code>iothreads</code> select
        which vCPUs/IOThreads this setting applies to, leaving them out sets the
        default.  The element <code>emulatorsched</code> does not have that
        attribute. Valid <code>vcpus</code> values start at 0 through one less
        than the number of vCPU's defined for the
        domain. Valid <code>iothreads</code> values are described in
        the <code>iothreadids</code>
        <a href="#elementsIOThreadsAllocation"><code>description</code></a>.
        If no <code>iothreadids</code> are defined, then libvirt numbers
        IOThreads from 1 to the number of <code>iothreads</code> available
        for the domain. For real-time schedulers (<code>fifo</code>,
        <code>rr</code>), priority must be specified as
        well (and is ignored for non-real-time ones). The value range
        for the priority depends on the host kernel (usually 1-99).
        <span class="since">Since 1.2.13</span>
        <code>emulatorsched</code> <span class="since">since 5.3.0</span>
      </dd>

      <dt><code>cachetune</code><span class="since">Since 4.1.0</span></dt>
      <dd>
        Optional <code>cachetune</code> element can control allocations for CPU
        caches using the resctrl on the host. Whether or not is this supported
        can be gathered from capabilities where some limitations like minimum
        size and required granularity are reported as well. The required
        attribute <code>vcpus</code> specifies to which vCPUs this allocation
        applies. A vCPU can only be member of one <code>cachetune</code> element
        allocation. The vCPUs specified by cachetune can be identical with those
        in memorytune, however they are not allowed to overlap.
        Supported subelements are:
        <dl>
          <dt><code>cache</code></dt>
          <dd>
            This optional element controls the allocation of CPU cache and has
            the following attributes:
            <dl>
              <dt><code>level</code></dt>
              <dd>
                Host cache level from which to allocate.
              </dd>
              <dt><code>id</code></dt>
              <dd>
                Host cache id from which to allocate.
              </dd>
              <dt><code>type</code></dt>
              <dd>
                Type of allocation. Can be <code>code</code> for code
                (instructions), <code>data</code> for data or <code>both</code>
                for both code and data (unified). Currently the allocation can
                be done only with the same type as the host supports, meaning
                you cannot request <code>both</code> for host with CDP
                (code/data prioritization) enabled.
              </dd>
              <dt><code>size</code></dt>
              <dd>
                The size of the region to allocate. The value by default is in
                bytes, but the <code>unit</code> attribute can be used to scale
                the value.
              </dd>
              <dt><code>unit</code> (optional)</dt>
              <dd>
                If specified it is the unit such as KiB, MiB, GiB, or TiB
                (described in the <code>memory</code> element
                for <a href="#elementsMemoryAllocation">Memory Allocation</a>)
                in which <code>size</code> is specified, defaults to bytes.
              </dd>
            </dl>
          </dd>
          <dt><code>monitor</code><span class="since">Since 4.10.0</span></dt>
          <dd>
            The optional element <code>monitor</code> creates the cache
            monitor(s) for current cache allocation and has the following
            required attributes:
            <dl>
              <dt><code>level</code></dt>
              <dd>
                Host cache level the monitor belongs to.
              </dd>
              <dt><code>vcpus</code></dt>
              <dd>
                vCPU list the monitor applies to. A monitor's vCPU list
                can only be the member(s) of the vCPU list of the associated
                allocation. The default monitor has the same vCPU list as the
                associated allocation. For non-default monitors, overlapping
                vCPUs are not permitted.
              </dd>
            </dl>
          </dd>
        </dl>
      </dd>

      <dt><code>memorytune</code><span class="since">Since 4.7.0</span></dt>
      <dd>
        Optional <code>memorytune</code> element can control allocations for
        memory bandwidth using the resctrl on the host. Whether or not is this
        supported can be gathered from capabilities where some limitations like
        minimum bandwidth and required granularity are reported as well. The
        required attribute <code>vcpus</code> specifies to which vCPUs this
        allocation applies. A vCPU can only be member of one
        <code>memorytune</code> element allocation. The <code>vcpus</code> specified
        by <code>memorytune</code> can be identical to those specified by
        <code>cachetune</code>. However they are not allowed to overlap each other.
        Supported subelements are:
        <dl>
          <dt><code>node</code></dt>
          <dd>
            This element controls the allocation of CPU memory bandwidth and has the
            following attributes:
            <dl>
              <dt><code>id</code></dt>
              <dd>
                Host node id from which to allocate memory bandwidth.
              </dd>
              <dt><code>bandwidth</code></dt>
              <dd>
                The memory bandwidth to allocate from this node. The value by default
                is in percentage.
              </dd>
            </dl>
          </dd>
        </dl>
      </dd>
    </dl>


    <h3><a id="elementsMemoryAllocation">Memory Allocation</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;maxMemory slots='16' unit='KiB'&gt;1524288&lt;/maxMemory&gt;
  &lt;memory unit='KiB'&gt;524288&lt;/memory&gt;
  &lt;currentMemory unit='KiB'&gt;524288&lt;/currentMemory&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>memory</code></dt>
      <dd>The maximum allocation of memory for the guest at boot time. The
        memory allocation includes possible additional memory devices specified
        at start or hotplugged later.
        The units for this value are determined by the optional
        attribute <code>unit</code>, which defaults to "KiB"
        (kibibytes, 2<sup>10</sup> or blocks of 1024 bytes).  Valid
        units are "b" or "bytes" for bytes, "KB" for kilobytes
        (10<sup>3</sup> or 1,000 bytes), "k" or "KiB" for kibibytes
        (1024 bytes), "MB" for megabytes (10<sup>6</sup> or 1,000,000
        bytes), "M" or "MiB" for mebibytes (2<sup>20</sup> or
        1,048,576 bytes), "GB" for gigabytes (10<sup>9</sup> or
        1,000,000,000 bytes), "G" or "GiB" for gibibytes
        (2<sup>30</sup> or 1,073,741,824 bytes), "TB" for terabytes
        (10<sup>12</sup> or 1,000,000,000,000 bytes), or "T" or "TiB"
        for tebibytes (2<sup>40</sup> or 1,099,511,627,776 bytes).
        However, the value will be rounded up to the nearest kibibyte
        by libvirt, and may be further rounded to the granularity
        supported by the hypervisor.  Some hypervisors also enforce a
        minimum, such as 4000KiB.

        In case <a href="#elementsCPU">NUMA</a> is configured for the guest the
        <code>memory</code> element can be omitted.

        In the case of crash, optional attribute <code>dumpCore</code>
        can be used to control whether the guest memory should be
        included in the generated coredump or not (values "on", "off").

        <span class='since'><code>unit</code> since 0.9.11</span>,
        <span class='since'><code>dumpCore</code> since 0.10.2
        (QEMU only)</span></dd>
      <dt><code>maxMemory</code></dt>
      <dd>The run time maximum memory allocation of the guest. The initial
        memory specified by either the <code>&lt;memory&gt;</code> element or
        the NUMA cell size configuration can be increased by hot-plugging of
        memory to the limit specified by this element.

        The <code>unit</code> attribute behaves the same as for
        <code>&lt;memory&gt;</code>.

        The <code>slots</code> attribute specifies the number of slots
        available for adding memory to the guest. The bounds are hypervisor
        specific.

        Note that due to alignment of the memory chunks added via memory
        hotplug the full size allocation specified by this element may be
        impossible to achieve.
        <span class='since'>Since 1.2.14 supported by the QEMU driver.</span>
      </dd>

      <dt><code>currentMemory</code></dt>
      <dd>The actual allocation of memory for the guest. This value can
        be less than the maximum allocation, to allow for ballooning
        up the guests memory on the fly. If this is omitted, it defaults
        to the same value as the <code>memory</code> element.
        The <code>unit</code> attribute behaves the same as
        for <code>memory</code>.</dd>
    </dl>


    <h3><a id="elementsMemoryBacking">Memory Backing</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;memoryBacking&gt;
    &lt;hugepages&gt;
      &lt;page size="1" unit="G" nodeset="0-3,5"/&gt;
      &lt;page size="2" unit="M" nodeset="4"/&gt;
    &lt;/hugepages&gt;
    &lt;nosharepages/&gt;
    &lt;locked/&gt;
    &lt;source type="file|anonymous|memfd"/&gt;
    &lt;access mode="shared|private"/&gt;
    &lt;allocation mode="immediate|ondemand"/&gt;
    &lt;discard/&gt;
  &lt;/memoryBacking&gt;
  ...
&lt;/domain&gt;
</pre>

    <p>The optional <code>memoryBacking</code> element may contain several
      elements that influence how virtual memory pages are backed by host
      pages.</p>

    <dl>
      <dt><code>hugepages</code></dt>
      <dd>This tells the hypervisor that the guest should have its memory
      allocated using hugepages instead of the normal native page size.
      <span class='since'>Since 1.2.5</span> it's possible to set hugepages
      more specifically per numa node. The <code>page</code> element is
      introduced. It has one compulsory attribute <code>size</code> which
      specifies which hugepages should be used (especially useful on systems
      supporting hugepages of different sizes). The default unit for the
      <code>size</code> attribute is kilobytes (multiplier of 1024). If you
      want to use different unit, use optional <code>unit</code> attribute.
      For systems with NUMA, the optional <code>nodeset</code> attribute may
      come handy as it ties given guest's NUMA nodes to certain hugepage
      sizes. From the example snippet, one gigabyte hugepages are used for
      every NUMA node except node number four. For the correct syntax see
      <a href="#elementsNUMATuning">this</a>.</dd>
      <dt><code>nosharepages</code></dt>
      <dd>Instructs hypervisor to disable shared pages (memory merge, KSM) for
        this domain. <span class="since">Since 1.0.6</span></dd>
      <dt><code>locked</code></dt>
      <dd>When set and supported by the hypervisor, memory pages belonging
        to the domain will be locked in host's memory and the host will not
        be allowed to swap them out, which might be required for some
        workloads such as real-time. For QEMU/KVM guests, the memory used by
        the QEMU process itself will be locked too: unlike guest memory, this
        is an amount libvirt has no way of figuring out in advance, so it has
        to remove the limit on locked memory altogether. Thus, enabling this
        option opens up to a potential security risk: the host will be unable
        to reclaim the locked memory back from the guest when it's running out
        of memory, which means a malicious guest allocating large amounts of
        locked memory could cause a denial-of-service attack on the host.
        Because of this, using this option is discouraged unless your workload
        demands it; even then, it's highly recommended to set a
        <code>hard_limit</code> (see
        <a href="#elementsMemoryTuning">memory tuning</a>) on memory allocation
        suitable for the specific environment at the same time to mitigate
        the risks described above. <span class="since">Since 1.0.6</span></dd>
       <dt><code>source</code></dt>
       <dd>Using the <code>type</code> attribute, it's possible to
       provide "file" to utilize file memorybacking or keep the
       default "anonymous". <span class="since">Since 4.10.0</span>,
       you may choose "memfd" backing. (QEMU/KVM only)</dd>
       <dt><code>access</code></dt>
       <dd>Using the <code>mode</code> attribute, specify if the memory is
         to be "shared" or "private". This can be overridden per numa node by
         <code>memAccess</code>.</dd>
       <dt><code>allocation</code></dt>
       <dd>Using the <code>mode</code> attribute, specify when to allocate
         the memory by supplying either "immediate" or "ondemand".</dd>
       <dt><code>discard</code></dt>
       <dd>When set and supported by hypervisor the memory
         content is discarded just before guest shuts down (or
         when DIMM module is unplugged). Please note that this is
         just an optimization and is not guaranteed to work in
         all cases (e.g. when hypervisor crashes).
         <span class="since">Since 4.4.0</span> (QEMU/KVM only)
       </dd>
    </dl>


    <h3><a id="elementsMemoryTuning">Memory Tuning</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;memtune&gt;
    &lt;hard_limit unit='G'&gt;1&lt;/hard_limit&gt;
    &lt;soft_limit unit='M'&gt;128&lt;/soft_limit&gt;
    &lt;swap_hard_limit unit='G'&gt;2&lt;/swap_hard_limit&gt;
    &lt;min_guarantee unit='bytes'&gt;67108864&lt;/min_guarantee&gt;
  &lt;/memtune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>memtune</code></dt>
      <dd> The optional <code>memtune</code> element provides details
        regarding the memory tunable parameters for the domain. If this is
        omitted, it defaults to the OS provided defaults. For QEMU/KVM, the
        parameters are applied to the QEMU process as a whole. Thus, when
        counting them, one needs to add up guest RAM, guest video RAM, and
        some memory overhead of QEMU itself. The last piece is hard to
        determine so one needs guess and try.  For each tunable, it
        is possible to designate which unit the number is in on
        input, using the same values as
        for <code>&lt;memory&gt;</code>.  For backwards
        compatibility, output is always in
        KiB.  <span class='since'><code>unit</code>
        since 0.9.11</span>
        Possible values for all *_limit parameters are in range from 0 to
        VIR_DOMAIN_MEMORY_PARAM_UNLIMITED.</dd>
      <dt><code>hard_limit</code></dt>
      <dd> The optional <code>hard_limit</code> element is the maximum memory
        the guest can use. The units for this value are kibibytes (i.e. blocks
        of 1024 bytes). Users of QEMU and KVM are strongly advised not to set
        this limit as domain may get killed by the kernel if the guess is too
        low, and determining the memory needed for a process to run is an
        <a href="http://en.wikipedia.org/wiki/Undecidable_problem">
        undecidable problem</a>; that said, if you already set
        <code>locked</code> in
        <a href="#elementsMemoryBacking">memory backing</a> because your
        workload demands it, you'll have to take into account the specifics of
        your deployment and figure out a value for <code>hard_limit</code> that
        is large enough to support the memory requirements of your guest, but
        small enough to protect your host against a malicious guest locking all
        memory.</dd>
      <dt><code>soft_limit</code></dt>
      <dd> The optional <code>soft_limit</code> element is the memory limit to
        enforce during memory contention. The units for this value are
        kibibytes (i.e. blocks of 1024 bytes)</dd>
      <dt><code>swap_hard_limit</code></dt>
      <dd> The optional <code>swap_hard_limit</code> element is the maximum
        memory plus swap the guest can use. The units for this value are
        kibibytes (i.e. blocks of 1024 bytes). This has to be more than
        hard_limit value provided</dd>
      <dt><code>min_guarantee</code></dt>
      <dd> The optional <code>min_guarantee</code> element is the guaranteed
        minimum memory allocation for the guest. The units for this value are
        kibibytes (i.e. blocks of 1024 bytes). This element is only supported
        by VMware ESX and OpenVZ drivers.</dd>
    </dl>


    <h3><a id="elementsNUMATuning">NUMA Node Tuning</a></h3>

<pre>
&lt;domain&gt;
  ...
  &lt;numatune&gt;
    &lt;memory mode="strict" nodeset="1-4,^3"/&gt;
    &lt;memnode cellid="0" mode="strict" nodeset="1"/&gt;
    &lt;memnode cellid="2" mode="preferred" nodeset="2"/&gt;
  &lt;/numatune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>numatune</code></dt>
      <dd>
        The optional <code>numatune</code> element provides details of
        how to tune the performance of a NUMA host via controlling NUMA policy
        for domain process. NB, only supported by QEMU driver.
        <span class='since'>Since 0.9.3</span>
      </dd>
      <dt><code>memory</code></dt>
      <dd>
        The optional <code>memory</code> element specifies how to allocate memory
        for the domain process on a NUMA host. It contains several optional
        attributes. Attribute <code>mode</code> is either 'interleave',
        'strict', or 'preferred', defaults to 'strict'. Attribute
        <code>nodeset</code> specifies the NUMA nodes, using the same syntax as
        attribute <code>cpuset</code> of element <code>vcpu</code>. Attribute
        <code>placement</code> (<span class='since'>since 0.9.12</span>) can be
        used to indicate the memory placement mode for domain process, its value
        can be either "static" or "auto", defaults to <code>placement</code> of
        <code>vcpu</code>, or "static" if <code>nodeset</code> is specified.
        "auto" indicates the domain process will only allocate memory from the
        advisory nodeset returned from querying numad, and the value of attribute
        <code>nodeset</code> will be ignored if it's specified.

        If <code>placement</code> of <code>vcpu</code> is 'auto', and
        <code>numatune</code> is not specified, a default <code>numatune</code>
        with <code>placement</code> 'auto' and <code>mode</code> 'strict' will
        be added implicitly.

        <span class='since'>Since 0.9.3</span>
      </dd>
      <dt><code>memnode</code></dt>
      <dd>
        Optional <code>memnode</code> elements can specify memory allocation
        policies per each guest NUMA node.  For those nodes having no
        corresponding <code>memnode</code> element, the default from
        element <code>memory</code> will be used.  Attribute <code>cellid</code>
        addresses guest NUMA node for which the settings are applied.
        Attributes <code>mode</code> and <code>nodeset</code> have the same
        meaning and syntax as in <code>memory</code> element.

        This setting is not compatible with automatic placement.
        <span class='since'>QEMU Since 1.2.7</span>
      </dd>
    </dl>


    <h3><a id="elementsBlockTuning">Block I/O Tuning</a></h3>
<pre>
&lt;domain&gt;
  ...
  &lt;blkiotune&gt;
    &lt;weight&gt;800&lt;/weight&gt;
    &lt;device&gt;
      &lt;path&gt;/dev/sda&lt;/path&gt;
      &lt;weight&gt;1000&lt;/weight&gt;
    &lt;/device&gt;
    &lt;device&gt;
      &lt;path&gt;/dev/sdb&lt;/path&gt;
      &lt;weight&gt;500&lt;/weight&gt;
      &lt;read_bytes_sec&gt;10000&lt;/read_bytes_sec&gt;
      &lt;write_bytes_sec&gt;10000&lt;/write_bytes_sec&gt;
      &lt;read_iops_sec&gt;20000&lt;/read_iops_sec&gt;
      &lt;write_iops_sec&gt;20000&lt;/write_iops_sec&gt;
    &lt;/device&gt;
  &lt;/blkiotune&gt;
  ...
&lt;/domain&gt;
</pre>

    <dl>
      <dt><code>blkiotune</code></dt>
      <dd> The optional <code>blkiotune</code> element provides the ability
        to tune Blkio cgroup tunable parameters for the domain. If this is
        omitted, it defaults to the OS provided
        defaults. <span class="since">Since 0.8.8</span></dd>
      <dt><code>weight</code></dt>
      <dd> The optional <code>weight</code> element is the overall I/O
        weight of the guest. The value should be in the range [100,
        1000]. After kernel 2.6.39, the value could be in the
        range [10, 1000].</dd>
      <dt><code>device</code></dt>
      <dd>The domain may have multiple <code>device</code> elements
        that further tune the weights for each host block device in
        use by the domain.  Note that
        multiple <a href="#elementsDisks">guest disks</a> can share a
        single host block device, if they are backed by files within
        the same host file system, which is why this tuning parameter
        is at the global domain level rather than associated with each
        guest disk device (contrast this to
        the <a href="#elementsDisks"><code>&lt;iotune&gt;</code></a>
        element which can apply to an
        individual <code>&lt;disk&gt;</code>).
        Each <code>device</code> element has two
        mandatory sub-elements, <code>path</code> describing the
        absolute path of the device, and <code>weight</code> giving
        the relative weight of that device, in the range [100,
        1000]. After kernel 2.6.39, the value could be in the
        range [10, 1000]. <span class="since">Since 0.9.8</span><br/>
        Additionally, the following optional sub-elements can be used:
        <dl>
          <dt><code>read_bytes_sec</code></dt>
          <dd>Read throughput limit in bytes per second.
            <span class="since">Since 1.2.2</span></dd>
          <dt><code>write_bytes_sec</code></dt>
          <dd>Write throughput limit in bytes per second.
            <span class="since">Since 1.2.2</span></dd>
          <dt><code>read_iops_sec</code></dt>
          <dd>Read I/O operations per second limit.
            <span class="since">Since 1.2.2</span></dd>
          <dt><code>write_iops_sec</code></dt>
          <dd>Write I/O operations per second limit.
            <span class="since">Since 1.2.2</span></dd>
      </dl></dd></dl>


    <h3><a id="resPartition">Resource partitioning</a></h3>

    <p>
      Hypervisors may allow for virtual machines to be placed into
      resource partitions, potentially with nesting of said partitions.
      The <code>resource</code> element groups together configuration
      related to resource partitioning. It currently supports a child
      element <code>partition</code> whose content defines the absolute path
      of the resource partition in which to place the domain. If no
      partition is listed, then the domain will be placed in a default
      partition. It is the responsibility of the app/admin to ensure
      that the partition exists prior to starting the guest. Only the
      (hypervisor specific) default partition can be assumed to exist
      by default.
    </p>
<pre>
...
&lt;resource&gt;
  &lt;partition&gt;/virtualmachines/production&lt;/partition&gt;
&lt;/resource&gt;
...
</pre>

    <p>
      Resource partitions are currently supported by the QEMU and
      LXC drivers, which map partition paths to cgroups directories,
      in all mounted controllers. <span class="since">Since 1.0.5</span>
    </p>

    <h3><a id="elementsCPU">CPU model and topology</a></h3>

    <p>
      Requirements for CPU model, its features and topology can be specified
      using the following collection of elements.
      <span class="since">Since 0.7.5</span>
    </p>

<pre>
...
&lt;cpu match='exact'&gt;
  &lt;model fallback='allow'&gt;core2duo&lt;/model&gt;
  &lt;vendor&gt;Intel&lt;/vendor&gt;
  &lt;topology sockets='1' cores='2' threads='1'/&gt;
  &lt;cache level='3' mode='emulate'/&gt;
  &lt;feature policy='disable' name='lahf_lm'/&gt;
&lt;/cpu&gt;
...</pre>

<pre>
&lt;cpu mode='host-model'&gt;
  &lt;model fallback='forbid'/&gt;
  &lt;topology sockets='1' cores='2' threads='1'/&gt;
&lt;/cpu&gt;
...</pre>

<pre>
&lt;cpu mode='host-passthrough'&gt;
  &lt;cache mode='passthrough'/&gt;
  &lt;feature policy='disable' name='lahf_lm'/&gt;
...</pre>

    <p>
      In case no restrictions need to be put on CPU model and its features, a
      simpler <code>cpu</code> element can be used.
      <span class="since">Since 0.7.6</span>
    </p>

<pre>
...
&lt;cpu&gt;
  &lt;topology sockets='1' cores='2' threads='1'/&gt;
&lt;/cpu&gt;
...</pre>

    <dl>
      <dt><code>cpu</code></dt>
      <dd>The <code>cpu</code> element is the main container for describing
        guest CPU requirements. Its <code>match</code> attribute specifies how
        strictly the virtual CPU provided to the guest matches these
        requirements. <span class="since">Since 0.7.6</span> the
        <code>match</code> attribute can be omitted if <code>topology</code>
        is the only element within <code>cpu</code>. Possible values for the
        <code>match</code> attribute are:

        <dl>
          <dt><code>minimum</code></dt>
          <dd>The specified CPU model and features describes the minimum
            requested CPU. A better CPU will be provided to the guest if it
            is possible with the requested hypervisor on the current host.
            This is a constrained <code>host-model</code> mode; the domain
            will not be created if the provided virtual CPU does not meet
            the requirements.</dd>

          <dt><code>exact</code></dt>
          <dd>The virtual CPU provided to the guest should exactly match the
            specification. If such CPU is not supported, libvirt will refuse
            to start the domain.</dd>

          <dt><code>strict</code></dt>
          <dd>The domain will not be created unless the host CPU exactly
            matches the specification. This is not very useful in practice
            and should only be used if there is a real reason.</dd>
        </dl>

        <span class="since">Since 0.8.5</span> the <code>match</code>
        attribute can be omitted and will default to <code>exact</code>.

        Sometimes the hypervisor is not able to create a virtual CPU exactly
        matching the specification passed by libvirt.
        <span class="since">Since 3.2.0</span>, an optional <code>check</code>
        attribute can be used to request a specific way of checking whether
        the virtual CPU matches the specification. It is usually safe to omit
        this attribute when starting a domain and stick with the default
        value. Once the domain starts, libvirt will automatically change the
        <code>check</code> attribute to the best supported value to ensure the
        virtual CPU does not change when the domain is migrated to another
        host. The following values can be used:

        <dl>
          <dt><code>none</code></dt>
          <dd>Libvirt does no checking and it is up to the hypervisor to
            refuse to start the domain if it cannot provide the requested CPU.
            With QEMU this means no checking is done at all since the default
            behavior of QEMU is to emit warnings, but start the domain anyway.
          </dd>

          <dt><code>partial</code></dt>
          <dd>Libvirt will check the guest CPU specification before starting
            a domain, but the rest is left on the hypervisor. It can still
            provide a different virtual CPU.</dd>

          <dt><code>full</code></dt>
          <dd>The virtual CPU created by the hypervisor will be checked
            against the CPU specification and the domain will not be started
            unless the two CPUs match.</dd>
        </dl>

        <span class="since">Since 0.9.10</span>, an optional <code>mode</code>
        attribute may be used to make it easier to configure a guest CPU to be
        as close to host CPU as possible. Possible values for the
        <code>mode</code> attribute are:

        <dl>
          <dt><code>custom</code></dt>
          <dd>In this mode, the <code>cpu</code> element describes the CPU
          that should be presented to the guest. This is the default when no
          <code>mode</code> attribute is specified. This mode makes it so that
          a persistent guest will see the same hardware no matter what host
          the guest is booted on.</dd>
          <dt><code>host-model</code></dt>
          <dd>The <code>host-model</code> mode is essentially a shortcut to
          copying host CPU definition from capabilities XML into domain XML.
          Since the CPU definition is copied just before starting a domain,
          exactly the same XML can be used on different hosts while still
          providing the best guest CPU each host supports. The
          <code>match</code> attribute can't be used in this mode. Specifying
          CPU model is not supported either, but <code>model</code>'s
          <code>fallback</code> attribute may still be used. Using the
          <code>feature</code> element, specific flags may be enabled or
          disabled specifically in addition to the host model. This may be
          used to fine tune features that can be emulated.
          <span class="since">(Since 1.1.1)</span>.
          Libvirt does not model every aspect of each CPU so
          the guest CPU will not match the host CPU exactly. On the other
          hand, the ABI provided to the guest is reproducible. During
          migration, complete CPU model definition is transferred to the
          destination host so the migrated guest will see exactly the same CPU
          model even if the destination host contains more capable CPUs for
          the running instance of the guest; but shutting down and restarting
          the guest may present different hardware to the guest according to
          the capabilities of the new host. Prior to libvirt 3.2.0 and QEMU
          2.9.0 detection of the host CPU model via QEMU is not supported.
          Thus the CPU configuration created using <code>host-model</code>
          may not work as expected.
          <span class="since">Since 3.2.0 and QEMU 2.9.0</span> this mode
          works the way it was designed and it is indicated by the
          <code>fallback</code> attribute set to <code>forbid</code> in the
          host-model CPU definition advertised in
          <a href="formatdomaincaps.html#elementsCPU">domain capabilities XML</a>.
          When <code>fallback</code> attribute is set to <code>allow</code>
          in the domain capabilities XML, it is recommended to use
          <code>custom</code> mode with just the CPU model from the host
          capabilities XML. <span class="since">Since 1.2.11</span> PowerISA
          allows processors to run VMs in binary compatibility mode supporting
          an older version of ISA.  Libvirt on PowerPC architecture uses the
          <code>host-model</code> to signify a guest mode CPU running in
          binary compatibility mode. Example:
          When a user needs a power7 VM to run in compatibility mode
          on a Power8 host, this can be described in XML as follows :
<pre>
&lt;cpu mode='host-model'&gt;
  &lt;model&gt;power7&lt;/model&gt;
&lt;/cpu&gt;
...</pre>
          </dd>
          <dt><code>host-passthrough</code></dt>
          <dd>With this mode, the CPU visible to the guest should be exactly
          the same as the host CPU even in the aspects that libvirt does not
          understand. Though the downside of this mode is that the guest
          environment cannot be reproduced on different hardware. Thus, if you
          hit any bugs, you are on your own. Further details of that CPU can
          be changed using <code>feature</code> elements. Migration of a guest
          using host-passthrough is dangerous if the source and destination
          hosts are not identical in both hardware and configuration. If such
          a migration is attempted then the guest may hang or crash upon
          resuming execution on the destination host.</dd>
        </dl>

        Both <code>host-model</code> and <code>host-passthrough</code> modes
        make sense when a domain can run directly on the host CPUs (for
        example, domains with type <code>kvm</code>). The actual host CPU is
        irrelevant for domains with emulated virtual CPUs (such as domains with
        type <code>qemu</code>). However, for backward compatibility
        <code>host-model</code> may be implemented even for domains running on
        emulated CPUs in which case the best CPU the hypervisor is able to
        emulate may be used rather then trying to mimic the host CPU model.
      </dd>

      <dt><code>model</code></dt>
      <dd>The content of the <code>model</code> element specifies CPU model
        requested by the guest. The list of available CPU models and their
        definition can be found in <code>cpu_map.xml</code> file installed
        in libvirt's data directory. If a hypervisor is not able to use the
        exact CPU model, libvirt automatically falls back to a closest model
        supported by the hypervisor while maintaining the list of CPU
        features. <span class="since">Since 0.9.10</span>, an optional
        <code>fallback</code> attribute can be used to forbid this behavior,
        in which case an attempt to start a domain requesting an unsupported
        CPU model will fail. Supported values for <code>fallback</code>
        attribute are: <code>allow</code> (this is the default), and
        <code>forbid</code>. The optional <code>vendor_id</code> attribute
        (<span class="since">Since 0.10.0</span>)  can be used to set the
        vendor id seen by the guest. It must be exactly 12 characters long.
        If not set the vendor id of the host is used. Typical possible
        values are "AuthenticAMD" and "GenuineIntel".</dd>

      <dt><code>vendor</code></dt>
      <dd><span class="since">Since 0.8.3</span> the content of the
        <code>vendor</code> element specifies CPU vendor requested by the
        guest. If this element is missing, the guest can be run on a CPU
        matching given features regardless on its vendor. The list of
        supported vendors can be found in <code>cpu_map.xml</code>.</dd>

      <dt><code>topology</code></dt>
      <dd>The <code>topology</code> element specifies requested topology of
        virtual CPU provided to the guest. Three non-zero values have to be
        given for <code>sockets</code>, <code>cores</code>, and
        <code>threads</code>: total number of CPU sockets, number of cores per
        socket, and number of threads per core, respectively. Hypervisors may
        require that the maximum number of vCPUs specified by the
        <code>cpus</code> element equals to the number of vcpus resulting
        from the topology.</dd>

      <dt><code>feature</code></dt>
      <dd>The <code>cpu</code> element can contain zero or more
        <code>elements</code> used to fine-tune features provided by the
        selected CPU model. The list of known feature names can be found in
        the same file as CPU models. The meaning of each <code>feature</code>
        element depends on its <code>policy</code> attribute, which has to be
        set to one of the following values:

        <dl>
          <dt><code>force</code></dt>
          <dd>The virtual CPU will claim the feature is supported regardless
            of it being supported by host CPU.</dd>
          <dt><code>require</code></dt>
          <dd>Guest creation will fail unless the feature is supported by the
            host CPU or the hypervisor is able to emulate it.</dd>
          <dt><code>optional</code></dt>
          <dd>The feature will be supported by virtual CPU if and only if it
            is supported by host CPU.</dd>
          <dt><code>disable</code></dt>
          <dd>The feature will not be supported by virtual CPU.</dd>
          <dt><code>forbid</code></dt>
          <dd>Guest creation will fail if the feature is supported by host
            CPU.</dd>
        </dl>

        <span class="since">Since 0.8.5</span> the <code>policy</code>
        attribute can be omitted and will default to <code>require</code>.

        <p> Individual CPU feature names are specified as part of the
        <code>name</code> attribute. For example, to explicitly specify
        the 'pcid' feature with Intel IvyBridge CPU model:
        </p>

<pre>
...
&lt;cpu match='exact'&gt;
  &lt;model fallback='forbid'&gt;IvyBridge&lt;/model&gt;
  &lt;vendor&gt;Intel&lt;/vendor&gt;
  &lt;feature policy='require' name='pcid'/&gt;
&lt;/cpu&gt;
...</pre>

      </dd>

      <dt><code>cache</code></dt>
      <dd><span class="since">Since 3.3.0</span> the <code>cache</code>
        element describes the virtual CPU cache. If the element is missing,
        the hypervisor will use a sensible default.

        <dl>
          <dt><code>level</code></dt>
          <dd>This optional attribute specifies which cache level is described
            by the element. Missing attribute means the element describes all
            CPU cache levels at once. Mixing <code>cache</code> elements with
            the <code>level</code> attribute set and those without the
            attribute is forbidden.</dd>

          <dt><code>mode</code></dt>
          <dd>
            The following values are supported:
            <dl>
              <dt><code>emulate</code></dt>
              <dd>The hypervisor will provide a fake CPU cache data.</dd>

              <dt><code>passthrough</code></dt>
              <dd>The real CPU cache data reported by the host CPU will be
                passed through to the virtual CPU.</dd>

              <dt><code>disable</code></dt>
              <dd>The virtual CPU will report no CPU cache of the specified
                level (or no cache at all if the <code>level</code> attribute
                is missing).</dd>
            </dl>
          </dd>
        </dl>
      </dd>
    </dl>

    <p>
      Guest NUMA topology can be specified using the <code>numa</code> element.
      <span class="since">Since 0.9.8</span>
    </p>

<pre>
...
&lt;cpu&gt;
  ...
  &lt;numa&gt;
    &lt;cell id='0' cpus='0-3' memory='512000' unit='KiB' discard='yes'/&gt;
    &lt;cell id='1' cpus='4-7' memory='512000' unit='KiB' memAccess='shared'/&gt;
  &lt;/numa&gt;
  ...
&lt;/cpu&gt;
...</pre>

    <p>
      Each <code>cell</code> element specifies a NUMA cell or a NUMA node.
      <code>cpus</code> specifies the CPU or range of CPUs that are
      part of the node. <code>memory</code> specifies the node memory
      in kibibytes (i.e. blocks of 1024 bytes).
      <span class="since">Since 1.2.11</span> one can use an additional <a
          href="#elementsMemoryAllocation"><code>unit</code></a> attribute to
      define units in which <code>memory</code> is specified.
      <span class="since">Since 1.2.7</span> all cells should
      have <code>id</code> attribute in case referring to some cell is
      necessary in the code, otherwise the cells are
      assigned <code>id</code>s in the increasing order starting from
      0.  Mixing cells with and without the <code>id</code> attribute
      is not recommended as it may result in unwanted behaviour.

      <span class='since'>Since 1.2.9</span> the optional attribute
      <code>memAccess</code> can control whether the memory is to be
      mapped as "shared" or "private".  This is valid only for
      hugepages-backed memory and nvdimm modules.

      Each <code>cell</code> element can have an optional
      <code>discard</code> attribute which fine tunes the discard
      feature for given numa node as described under
      <a href="#elementsMemoryBacking">Memory Backing</a>.
      Accepted values are <code>yes</code> and <code>no</code>.
      <span class='since'>Since 4.4.0</span>
    </p>

    <p>
      This guest NUMA specification is currently available only for
      QEMU/KVM and Xen.
    </p>

    <p>
      A NUMA hardware architecture supports the notion of distances
      between NUMA cells. <span class="since">Since 3.10.0</span> it
      is possible to define the distance between NUMA cells using the
      <code>distances</code> element within a NUMA <code>cell</code>
      description. The <code>sibling</code> sub-element is used to
      specify the distance value between sibling NUMA cells. For more
      details, see the chapter explaining the system's SLIT (System
      Locality Information Table) within the ACPI (Advanced
      Configuration and Power Interface) specification.
    </p>

<pre>
...
&lt;cpu&gt;
  ...
  &lt;numa&gt;
    &lt;cell id='0' cpus='0,4-7' memory='512000' unit='KiB'&gt;
      &lt;distances&gt;
        &lt;sibling id='0' value='10'/&gt;
        &lt;sibling id='1' value='21'/&gt;
        &lt;sibling id='2' value='31'/&gt;
        &lt;sibling id='3' value='41'/&gt;
      &lt;/distances&gt;
    &lt;/cell&gt;
    &lt;cell id='1' cpus='1,8-10,12-15' memory='512000' unit='KiB' memAccess='shared'&gt;
      &lt;distances&gt;
        &lt;sibling id='0' value='21'/&gt;
        &lt;sibling id='1' value='10'/&gt;
        &lt;sibling id='2' value='21'/&gt;
        &lt;sibling id='3' value='31'/&gt;
      &lt;/distances&gt;
    &lt;/cell&gt;
    &lt;cell id='2' cpus='2,11' memory='512000' unit='KiB' memAccess='shared'&gt;
      &lt;distances&gt;
        &lt;sibling id='0' value='31'/&gt;
        &lt;sibling id='1' value='21'/&gt;
        &lt;sibling id='2' value='10'/&gt;
        &lt;sibling id='3' value='21'/&gt;
      &lt;/distances&gt;
    &lt;/cell&gt;
    &lt;cell id='3' cpus='3' memory='512000' unit='KiB'&gt;
      &lt;distances&gt;
        &lt;sibling id='0' value='41'/&gt;
        &lt;sibling id='1' value='31'/&gt;
        &lt;sibling id='2' value='21'/&gt;
        &lt;sibling id='3' value='10'/&gt;
      &lt;/distances&gt;
    &lt;/cell&gt;
  &lt;/numa&gt;
  ...
&lt;/cpu&gt;
...</pre>

    <p>
      Describing distances between NUMA cells is currently only supported
      by Xen and QEMU. If no <code>distances</code> are given to describe
      the SLIT data between different cells, it will default to a scheme
      using 10 for local and 20 for remote distances.
    </p>

    <h3><a id="elementsEvents">Events configuration</a></h3>

    <p>
      It is sometimes necessary to override the default actions taken
      on various events. Not all hypervisors support all events and actions.
      The actions may be taken as a result of calls to libvirt APIs
      <a href="html/libvirt-libvirt-domain.html#virDomainReboot">
        <code>virDomainReboot</code>
      </a>,
      <a href="html/libvirt-libvirt-domain.html#virDomainShutdown">
        <code>virDomainShutdown</code>
      </a>,
      or
      <a href="html/libvirt-libvirt-domain.html#virDomainShutdownFlags">
        <code>virDomainShutdownFlags</code>
      </a>.
      Using <code>virsh reboot</code> or <code>virsh shutdown</code> would
      also trigger the event.
    </p>

<pre>
...
&lt;on_poweroff&gt;destroy&lt;/on_poweroff&gt;
&lt;on_reboot&gt;restart&lt;/on_reboot&gt;
&lt;on_crash&gt;restart&lt;/on_crash&gt;
&lt;on_lockfailure&gt;poweroff&lt;/on_lockfailure&gt;
...</pre>

    <p>
      The following collections of elements allow the actions to be
      specified when a guest OS triggers a lifecycle operation. A
      common use case is to force a reboot to be treated as a poweroff
      when doing the initial OS installation. This allows the VM to be
      re-configured for the first post-install bootup.
    </p>
    <dl>
      <dt><code>on_poweroff</code></dt>
      <dd>The content of this element specifies the action to take when
        the guest requests a poweroff.</dd>
      <dt><code>on_reboot</code></dt>
      <dd>The content of this element specifies the action to take when
        the guest requests a reboot.</dd>
      <dt><code>on_crash</code></dt>
      <dd>The content of this element specifies the action to take when
        the guest crashes.</dd>
    </dl>

    <p>
      Each of these states allow for the same four possible actions.
    </p>

    <dl>
      <dt><code>destroy</code></dt>
      <dd>The domain will be terminated completely and all resources
        released.</dd>
      <dt><code>restart</code></dt>
      <dd>The domain will be terminated and then restarted with
        the same configuration.</dd>
      <dt><code>preserve</code></dt>
      <dd>The domain will be terminated and its resource preserved
        to allow analysis.</dd>
      <dt><code>rename-restart</code></dt>
      <dd>The domain will be terminated and then restarted with
        a new name.</dd>
    </dl>

    <p>
    QEMU/KVM supports the <code>on_poweroff</code> and <code>on_reboot</code>
    events handling the <code>destroy</code> and <code>restart</code> actions.
    The <code>preserve</code> action for an <code>on_reboot</code> event
    is treated as a <code>destroy</code> and the <code>rename-restart</code>
    action for an <code>on_poweroff</code> event is treated as a
    <code>restart</code> event.
    </p>

    <p>
      The <code>on_crash</code> event supports these additional
      actions <span class="since">since 0.8.4</span>.
    </p>

    <dl>
      <dt><code>coredump-destroy</code></dt>
      <dd>The crashed domain's core will be dumped, and then the
        domain will be terminated completely and all resources
        released</dd>
      <dt><code>coredump-restart</code></dt>
      <dd>The crashed domain's core will be dumped, and then the
        domain will be restarted with the same configuration</dd>
    </dl>

    <p>
      <span class="since">Since 3.9.0</span>, the lifecycle events can
      be configured via the
      <a href="html/libvirt-libvirt-domain.html#virDomainSetLifecycleAction">
        <code>virDomainSetLifecycleAction</code></a> API.
    </p>

    <p>
      The <code>on_lockfailure</code> element (<span class="since">since
      1.0.0</span>) may be used to configure what action should be
      taken when a lock manager loses resource locks. The following
      actions are recognized by libvirt, although not all of them need
      to be supported by individual lock managers. When no action is
      specified, each lock manager will take its default action.
    </p>
    <dl>
      <dt><code>poweroff</code></dt>
      <dd>The domain will be forcefully powered off.</dd>
      <dt><code>restart</code></dt>
      <dd>The domain will be powered off and started up again to
        reacquire its locks.</dd>
      <dt><code>pause</code></dt>
      <dd>The domain will be paused so that it can be manually resumed
        when lock issues are solved.</dd>
      <dt><code>ignore</code></dt>
      <dd>Keep the domain running as if nothing happened.</dd>
    </dl>

    <h3><a id="elementsPowerManagement">Power Management</a></h3>

    <p>
      <span class="since">Since 0.10.2</span> it is possible to
      forcibly enable or disable BIOS advertisements to the guest
      OS. (NB: Only qemu driver support)
    </p>

<pre>
...
&lt;pm&gt;
  &lt;suspend-to-disk enabled='no'/&gt;
  &lt;suspend-to-mem enabled='yes'/&gt;
&lt;/pm&gt;
...</pre>

    <dl>
      <dt><code>pm</code></dt>
      <dd>These elements enable ('yes') or disable ('no') BIOS support
        for S3 (suspend-to-mem) and S4 (suspend-to-disk) ACPI sleep
        states. If nothing is specified, then the hypervisor will be
        left with its default value.<br/>
        Note: This setting cannot prevent the guest OS from performing
        a suspend as the guest OS itself can choose to circumvent the
        unavailability of the sleep states (e.g. S4 by turning off
        completely).</dd>
    </dl>

    <h3><a id="elementsFeatures">Hypervisor features</a></h3>

    <p>
      Hypervisors may allow certain CPU / machine features to be
      toggled on/off.
    </p>

<pre>
...
&lt;features&gt;
  &lt;pae/&gt;
  &lt;acpi/&gt;
  &lt;apic/&gt;
  &lt;hap/&gt;
  &lt;privnet/&gt;
  &lt;hyperv&gt;
    &lt;relaxed state='on'/&gt;
    &lt;vapic state='on'/&gt;
    &lt;spinlocks state='on' retries='4096'/&gt;
    &lt;vpindex state='on'/&gt;
    &lt;runtime state='on'/&gt;
    &lt;synic state='on'/&gt;
    &lt;stimer state='on'/&gt;
    &lt;reset state='on'/&gt;
    &lt;vendor_id state='on' value='KVM Hv'/&gt;
    &lt;frequencies state='on'/&gt;
    &lt;reenlightenment state='on'/&gt;
    &lt;tlbflush state='on'/&gt;
    &lt;ipi state='on'/&gt;
    &lt;evmcs state='on'/&gt;
  &lt;/hyperv&gt;
  &lt;kvm&gt;
    &lt;hidden state='on'/&gt;
  &lt;/kvm&gt;
  &lt;pvspinlock state='on'/&gt;
  &lt;gic version='2'/&gt;
  &lt;ioapic driver='qemu'/&gt;
  &lt;hpt resizing='required'&gt;
    &lt;maxpagesize unit='MiB'&gt;16&lt;/maxpagesize&gt;
  &lt;/hpt&gt;
  &lt;vmcoreinfo state='on'/&gt;
  &lt;smm state='on'&gt;
    &lt;tseg unit='MiB'&gt;48&lt;/tseg&gt;
  &lt;/smm&gt;
  &lt;htm state='on'/&gt;
  &lt;msrs unknown='ignore'/&gt;
&lt;/features&gt;
...</pre>

    <p>
      All features are listed within the <code>features</code>
      element, omitting a togglable feature tag turns it off.
      The available features can be found by asking
      for the <a href="formatcaps.html">capabilities XML</a> and
      <a href="formatdomaincaps.html">domain capabilities XML</a>,
      but a common set for fully virtualized domains are:
    </p>

    <dl>
      <dt><code>pae</code></dt>
      <dd>Physical address extension mode allows 32-bit guests
        to address more than 4 GB of memory.</dd>
      <dt><code>acpi</code></dt>
      <dd>ACPI is useful for power management, for example, with
        KVM guests it is required for graceful shutdown to work.
      </dd>
      <dt><code>apic</code></dt>
      <dd>APIC allows the use of programmable IRQ
      management. <span class="since">Since 0.10.2 (QEMU only)</span> there is
      an optional attribute <code>eoi</code> with values <code>on</code>
      and <code>off</code> which toggles the availability of EOI (End of
      Interrupt) for the guest.
      </dd>
      <dt><code>hap</code></dt>
      <dd>Depending on the <code>state</code> attribute (values <code>on</code>,
        <code>off</code>) enable or disable use of Hardware Assisted Paging.
        The default is <code>on</code> if the hypervisor detects availability
        of Hardware Assisted Paging.
      </dd>
      <dt><code>viridian</code></dt>
      <dd>Enable Viridian hypervisor extensions for paravirtualizing
        guest operating systems
      </dd>
      <dt><code>privnet</code></dt>
      <dd>Always create a private network namespace. This is
        automatically set if any interface devices are defined.
        This feature is only relevant for container based
        virtualization drivers, such as LXC.
      </dd>
      <dt><code>hyperv</code></dt>
      <dd>Enable various features improving behavior of guests
        running Microsoft Windows.
      <table class="top_table">
        <tr>
          <th>Feature</th>
          <th>Description</th>
          <th>Value</th>
          <th>Since</th>
        </tr>
        <tr>
          <td>relaxed</td>
          <td>Relax constraints on timers</td>
          <td>on, off</td>
          <td><span class="since">1.0.0 (QEMU 2.0)</span></td>
        </tr>
        <tr>
          <td>vapic</td>
          <td>Enable virtual APIC</td>
          <td>on, off</td>
          <td><span class="since">1.1.0 (QEMU 2.0)</span></td>
        </tr>
        <tr>
          <td>spinlocks</td>
          <td>Enable spinlock support</td>
          <td>on, off; retries - at least 4095</td>
          <td><span class="since">1.1.0 (QEMU 2.0)</span></td>
        </tr>
        <tr>
          <td>vpindex</td>
          <td>Virtual processor index</td>
          <td>on, off</td>
          <td><span class="since">1.3.3 (QEMU 2.5)</span></td>
        </tr>
        <tr>
          <td>runtime</td>
          <td>Processor time spent on running guest code and on behalf of guest code</td>
          <td>on, off</td>
          <td><span class="since">1.3.3 (QEMU 2.5)</span></td>
        </tr>
        <tr>
          <td>synic</td>
          <td>Enable Synthetic Interrupt Controller (SynIC)</td>
          <td>on, off</td>
          <td><span class="since">1.3.3 (QEMU 2.6)</span></td>
        </tr>
        <tr>
          <td>stimer</td>
          <td>Enable SynIC timers</td>
          <td>on, off</td>
          <td><span class="since">1.3.3 (QEMU 2.6)</span></td>
        </tr>
        <tr>
          <td>reset</td>
          <td>Enable hypervisor reset</td>
          <td>on, off</td>
          <td><span class="since">1.3.3 (QEMU 2.5)</span></td>
        </tr>
        <tr>
          <td>vendor_id</td>
          <td>Set hypervisor vendor id</td>
          <td>on, off; value - string, up to 12 characters</td>
          <td><span class="since">1.3.3 (QEMU 2.5)</span></td>
        </tr>
        <tr>
          <td>frequencies</td>
          <td>Expose frequency MSRs</td>
          <td>on, off</td>
          <td><span class="since">4.7.0 (QEMU 2.12)</span></td>
        </tr>
        <tr>
          <td>reenlightenment</td>
          <td>Enable re-enlightenment notification on migration</td>
          <td>on, off</td>
          <td><span class="since">4.7.0 (QEMU 3.0)</span></td>
        </tr>
        <tr>
          <td>tlbflush</td>
          <td>Enable PV TLB flush support</td>
          <td>on, off</td>
          <td><span class="since">4.7.0 (QEMU 3.0)</span></td>
        </tr>
        <tr>
          <td>ipi</td>
          <td>Enable PV IPI support</td>
          <td>on, off</td>
          <td><span class="since">4.10.0 (QEMU 3.1)</span></td>
        </tr>
        <tr>
          <td>evmcs</td>
          <td>Enable Enlightened VMCS</td>
          <td>on, off</td>
          <td><span class="since">4.10.0 (QEMU 3.1)</span></td>
        </tr>
      </table>
      </dd>
      <dt><code>pvspinlock</code></dt>
      <dd>Notify the guest that the host supports paravirtual spinlocks
          for example by exposing the pvticketlocks mechanism. This feature
          can be explicitly disabled by using <code>state='off'</code>
          attribute.
      </dd>
      <dt><code>kvm</code></dt>
      <dd>Various features to change the behavior of the KVM hypervisor.
      <table class="top_table">
        <tr>
          <th>Feature</th>
          <th>Description</th>
          <th>Value</th>
          <th>Since</th>
        </tr>
        <tr>
          <td>hidden</td>
          <td>Hide the KVM hypervisor from standard MSR based discovery</td>
          <td>on, off</td>
          <td><span class="since">1.2.8 (QEMU 2.1.0)</span></td>
        </tr>
      </table>
      </dd>
      <dt><code>pmu</code></dt>
      <dd>Depending on the <code>state</code> attribute (values <code>on</code>,
        <code>off</code>, default <code>on</code>) enable or disable the
        performance monitoring unit for the guest.
        <span class="since">Since 1.2.12</span>
      </dd>
      <dt><code>vmport</code></dt>
      <dd>Depending on the <code>state</code> attribute (values <code>on</code>,
        <code>off</code>, default <code>on</code>) enable or disable
        the emulation of VMware IO port, for vmmouse etc.
        <span class="since">Since 1.2.16</span>
      </dd>
      <dt><code>gic</code></dt>
      <dd>Enable for architectures using a General Interrupt
          Controller instead of APIC in order to handle interrupts.
          For example, the 'aarch64' architecture uses
          <code>gic</code> instead of <code>apic</code>. The optional
          attribute <code>version</code> specifies the GIC version;
          however, it may not be supported by all hypervisors. Accepted
          values are <code>2</code>, <code>3</code> and <code>host</code>.
          <span class="since">Since 1.2.16</span>
      </dd>
      <dt><code>smm</code></dt>
      <dd>
        <p>
          Depending on the <code>state</code> attribute (values <code>on</code>,
          <code>off</code>, default <code>on</code>) enable or disable
          System Management Mode.
          <span class="since">Since 2.1.0</span>
        </p><p> Optional sub-element <code>tseg</code> can be used to specify
          the amount of memory dedicated to SMM's extended TSEG. That offers a
          fourth option size apart from the existing ones (1 MiB, 2 MiB and 8
          MiB) that the guest OS (or rather loader) can choose from. The size
          can be specified as a value of that element, optional attribute
          <code>unit</code> can be used to specify the unit of the
          aforementioned value (defaults to 'MiB').  If set to 0 the extended
          size is not advertised and only the default ones (see above) are
          available.
        </p><p>
          <b>If the VM is booting you should leave this option alone, unless you
          are very certain you know what you are doing.</b>
        </p><p>
          This value is configurable due to the fact that the calculation cannot
          be done right with the guarantee that it will work correctly.  In
          QEMU, the user-configurable extended TSEG feature was unavailable up
          to and including <code>pc-q35-2.9</code>. Starting with
          <code>pc-q35-2.10</code> the feature is available, with default size
          16 MiB.  That should suffice for up to roughly 272 vCPUs, 5 GiB guest
          RAM in total, no hotplug memory range, and 32 GiB of 64-bit PCI MMIO
          aperture.  Or for 48 vCPUs, with 1TB of guest RAM, no hotplug DIMM
          range, and 32GB of 64-bit PCI MMIO aperture. The values may also vary
          based on the loader the VM is using.
        </p><p>
          Additional size might be needed for significantly higher vCPU counts
          or increased address space (that can be memory, maxMemory, 64-bit PCI
          MMIO aperture size; roughly 8 MiB of TSEG per 1 TiB of address space)
          which can also be rounded up.
        </p><p>
          Due to the nature of this setting being similar to "how much RAM
          should the guest have" users are advised to either consult the
          documentation of the guest OS or loader (if there is any), or test
          this by trial-and-error changing the value until the VM boots
          successfully.  Yet another guiding value for users might be the fact
          that 48 MiB should be enough for pretty large guests (240 vCPUs and
          4TB guest RAM), but it is on purpose not set as default as 48 MiB of
          unavailable RAM might be too much for small guests (e.g. with 512 MiB
          of RAM).
        </p><p>
          See <a href="#elementsMemoryAllocation">Memory Allocation</a>
          for more details about the <code>unit</code> attribute.
          <span class="since">Since 4.5.0</span> (QEMU only)
        </p>
      </dd>
      <dt><code>ioapic</code></dt>
      <dd>Tune the I/O APIC. Possible values for the
          <code>driver</code> attribute are:
          <code>kvm</code> (default for KVM domains)
          and <code>qemu</code> which puts I/O APIC in userspace
          which is also known as a split I/O APIC mode.
          <span class="since">Since 3.4.0</span> (QEMU/KVM only)
      </dd>
      <dt><code>hpt</code></dt>
      <dd>Configure the HPT (Hash Page Table) of a pSeries guest. Possible
          values for the <code>resizing</code> attribute are
          <code>enabled</code>, which causes HPT resizing to be enabled if
          both the guest and the host support it; <code>disabled</code>, which
          causes HPT resizing to be disabled regardless of guest and host
          support; and <code>required</code>, which prevents the guest from
          starting unless both the guest and the host support HPT resizing. If
          the attribute is not defined, the hypervisor default will be used.
          <span class="since">Since 3.10.0</span> (QEMU/KVM only).

          <p>The optional <code>maxpagesize</code> subelement can be used to
          limit the usable page size for HPT guests. Common values are 64 KiB,
          16 MiB and 16 GiB; when not specified, the hypervisor default will
          be used. <span class="since">Since 4.5.0</span> (QEMU/KVM only).</p>
      </dd>
      <dt><code>vmcoreinfo</code></dt>
      <dd>Enable QEMU vmcoreinfo device to let the guest kernel save debug
          details. <span class="since">Since 4.4.0</span> (QEMU only)
      </dd>
      <dt><code>htm</code></dt>
      <dd>Configure HTM (Hardware Transational Memory) availability for
          pSeries guests. Possible values for the <code>state</code> attribute
          are <code>on</code> and <code>off</code>. If the attribute is not
          defined, the hypervisor default will be used.
          <span class="since">Since 4.6.0</span> (QEMU/KVM only)
      </dd>
      <dt><code>nested-hv</code></dt>
      <dd>Configure nested HV availability for pSeries guests. This needs to
          be enabled from the host (L0) in order to be effective; having HV
          support in the (L1) guest is very desiderable if it's planned to
          run nested (L2) guests inside it, because it will result in those
          nested guests having much better performance than they would when
          using KVM PR or TCG.
          Possible values for the <code>state</code> attribute are
          <code>on</code> and <code>off</code>. If the attribute is not
          defined, the hypervisor default will be used.
          <span class="since">Since 4.10.0</span> (QEMU/KVM only)
      </dd>
      <dt><code>msrs</code></dt>
      <dd>Some guests might require ignoring unknown
          Model Specific Registers (MSRs) reads and writes. It's possible
          to switch this by setting <code>unknown</code> attribute
          of <code>msrs</code> to <code>ignore</code>. If the attribute is
          not defined, or set to <code>fault</code>, unknown reads and writes
          will not be ignored.
          <span class="since">Since 5.1.0</span> (bhyve only)
      </dd>
    </dl>

    <h3><a id="elementsTime">Time keeping</a></h3>

    <p>
      The guest clock is typically initialized from the host clock.
      Most operating systems expect the hardware clock to be kept
      in UTC, and this is the default. Windows, however, expects
      it to be in so called 'localtime'.
    </p>

<pre>
...
&lt;clock offset='localtime'&gt;
  &lt;timer name='rtc' tickpolicy='catchup' track='guest'&gt;
    &lt;catchup threshold='123' slew='120' limit='10000'/&gt;
  &lt;/timer&gt;
  &lt;timer name='pit' tickpolicy='delay'/&gt;
&lt;/clock&gt;
...</pre>

    <dl>
      <dt><code>clock</code></dt>
      <dd>
        <p>The <code>offset</code> attribute takes four possible
          values, allowing fine grained control over how the guest
          clock is synchronized to the host. NB, not all hypervisors
          support all modes.</p>
        <dl>
          <dt><code>utc</code></dt>
          <dd>
            The guest clock will always be synchronized to UTC when
            booted.
            <span class="since">Since 0.9.11</span> 'utc' mode can be converted
            to 'variable' mode, which can be controlled by using the
            <code>adjustment</code> attribute. If the value is 'reset', the
            conversion is never done (not all hypervisors can
            synchronize to UTC on each boot; use of 'reset' will cause
            an error on those hypervisors). A numeric value
            forces the conversion to 'variable' mode using the value as the
            initial adjustment. The default <code>adjustment</code> is
            hypervisor specific.
          </dd>
          <dt><code>localtime</code></dt>
          <dd>
            The guest clock will be synchronized to the host's configured
            timezone when booted, if any.
            <span class="since">Since 0.9.11,</span> the <code>adjustment</code>
            attribute behaves the same as in 'utc' mode.
          </dd>
          <dt><code>timezone</code></dt>
          <dd>
            The guest clock will be synchronized to the requested timezone
            using the <code>timezone</code> attribute.
            <span class="since">Since 0.7.7</span>
          </dd>
          <dt><code>variable</code></dt>
          <dd>
            The guest clock will have an arbitrary offset applied
            relative to UTC or localtime, depending on the <code>basis</code>
            attribute. The delta relative to UTC (or localtime) is specified
            in seconds, using the <code>adjustment</code> attribute.
            The guest is free to adjust the RTC over time and expect
            that it will be honored at next reboot. This is in
            contrast to 'utc' and 'localtime' mode (with the optional
            attribute adjustment='reset'), where the RTC adjustments are
            lost at each reboot. <span class="since">Since 0.7.7</span>
            <span class="since">Since 0.9.11</span> the <code>basis</code>
            attribute can be either 'utc' (default) or 'localtime'.
          </dd>
        </dl>
        <p>
          A <code>clock</code> may have zero or more
          <code>timer</code> sub-elements. <span class="since">Since
          0.8.0</span>
        </p>
      </dd>
      <dt><code>timer</code></dt>
      <dd>
        <p>
          Each timer element requires a <code>name</code> attribute,
          and has other optional attributes that depend on
          the <code>name</code> specified.  Various hypervisors
          support different combinations of attributes.
        </p>
        <dl>
          <dt><code>name</code></dt>
          <dd>
            The <code>name</code> attribute selects which timer is
            being modified, and can be one of
            "platform" (currently unsupported),
            "hpet" (libxl, xen, qemu), "kvmclock" (qemu),
            "pit" (qemu), "rtc" (qemu), "tsc" (libxl, qemu -
            <span class="since">since 3.2.0</span>)
            or "hypervclock"
            (qemu - <span class="since">since 1.2.2</span>).

            The <code>hypervclock</code> timer adds support for the
            reference time counter and the reference page for iTSC
            feature for guests running the Microsoft Windows
            operating system.
          </dd>
          <dt><code>track</code></dt>
          <dd>
            The <code>track</code> attribute specifies what the timer
            tracks, and can be "boot", "guest", or "wall".
            Only valid for <code>name="rtc"</code>
            or <code>name="platform"</code>.
          </dd>
          <dt><code>tickpolicy</code></dt>
          <dd>
            <p>
            The <code>tickpolicy</code> attribute determines what
            happens when QEMU misses a deadline for injecting a
            tick to the guest:
            </p>
            <dl>
              <dt><code>delay</code></dt>
              <dd>Continue to deliver ticks at the normal rate.
                The guest time will be delayed due to the late
                tick</dd>
              <dt><code>catchup</code></dt>
              <dd>Deliver ticks at a higher rate to catch up
                with the missed tick. The guest time should
                not be delayed once catchup is complete.</dd>
              <dt><code>merge</code></dt>
              <dd>Merge the missed tick(s) into one tick and
                inject. The guest time may be delayed, depending
                on how the OS reacts to the merging of ticks</dd>
              <dt><code>discard</code></dt>
              <dd>Throw away the missed tick(s) and continue
                with future injection normally. The guest time
                may be delayed, unless the OS has explicit
                handling of lost ticks</dd>
            </dl>
            <p>If the policy is "catchup", there can be further details in
            the <code>catchup</code> sub-element.</p>
            <dl>
              <dt><code>catchup</code></dt>
              <dd>
                The <code>catchup</code> element has three optional
                attributes, each a positive integer.  The attributes
                are <code>threshold</code>, <code>slew</code>,
                and <code>limit</code>.
              </dd>
            </dl>
            <p>
              Note that hypervisors are not required to support all policies across all time sources
            </p>
          </dd>
          <dt><code>frequency</code></dt>
          <dd>
            The <code>frequency</code> attribute is an unsigned
            integer specifying the frequency at
            which <code>name="tsc"</code> runs.
          </dd>
          <dt><code>mode</code></dt>
          <dd>
            The <code>mode</code> attribute controls how
            the <code>name="tsc"</code> timer is managed, and can be
            "auto", "native", "emulate", "paravirt", or "smpsafe".
            Other timers are always emulated.
          </dd>
          <dt><code>present</code></dt>
          <dd>
            The <code>present</code> attribute can be "yes" or "no" to
            specify whether a particular timer is available to the guest.
          </dd>
        </dl>
      </dd>
    </dl>

    <h3><a id="elementsPerf">Performance monitoring events</a></h3>

    <p>
      Some platforms allow monitoring of performance of the virtual machine and
      the code executed inside. To enable the performance monitoring events
      you can either specify them in the <code>perf</code> element or enable
      them via <code>virDomainSetPerfEvents</code> API. The performance values
      are then retrieved using the virConnectGetAllDomainStats API.
      <span class="since">Since 2.0.0</span>
    </p>

<pre>
...
&lt;perf&gt;
  &lt;event name='cmt' enabled='yes'/&gt;
  &lt;event name='mbmt' enabled='no'/&gt;
  &lt;event name='mbml' enabled='yes'/&gt;
  &lt;event name='cpu_cycles' enabled='no'/&gt;
  &lt;event name='instructions' enabled='yes'/&gt;
  &lt;event name='cache_references' enabled='no'/&gt;
  &lt;event name='cache_misses' enabled='no'/&gt;
  &lt;event name='branch_instructions' enabled='no'/&gt;
  &lt;event name='branch_misses' enabled='no'/&gt;
  &lt;event name='bus_cycles' enabled='no'/&gt;
  &lt;event name='stalled_cycles_frontend' enabled='no'/&gt;
  &lt;event name='stalled_cycles_backend' enabled='no'/&gt;
  &lt;event name='ref_cpu_cycles' enabled='no'/&gt;
  &lt;event name='cpu_clock' enabled='no'/&gt;
  &lt;event name='task_clock' enabled='no'/&gt;
  &lt;event name='page_faults' enabled='no'/&gt;
  &lt;event name='context_switches' enabled='no'/&gt;
  &lt;event name='cpu_migrations' enabled='no'/&gt;
  &lt;event name='page_faults_min' enabled='no'/&gt;
  &lt;event name='page_faults_maj' enabled='no'/&gt;
  &lt;event name='alignment_faults' enabled='no'/&gt;
  &lt;event name='emulation_faults' enabled='no'/&gt;
&lt;/perf&gt;
...
</pre>

  <table class="top_table">
    <tr>
      <th>event name</th>
      <th>Description</th>
      <th>stats parameter name</th>
    </tr>
    <tr>
      <td><code>cmt</code></td>
      <td>usage of l3 cache in bytes by applications running on the platform</td>
      <td><code>perf.cmt</code></td>
    </tr>
    <tr>
      <td><code>mbmt</code></td>
      <td>total system bandwidth from one level of cache</td>
      <td><code>perf.mbmt</code></td>
    </tr>
    <tr>
      <td><code>mbml</code></td>
      <td>bandwidth of memory traffic for a memory controller</td>
      <td><code>perf.mbml</code></td>
    </tr>
    <tr>
      <td><code>cpu_cycles</code></td>
      <td>the count of CPU cycles (total/elapsed)</td>
      <td><code>perf.cpu_cycles</code></td>
    </tr>
    <tr>
      <td><code>instructions</code></td>
      <td>the count of instructions by applications running on the platform</td>
      <td><code>perf.instructions</code></td>
    </tr>
    <tr>
      <td><code>cache_references</code></td>
      <td>the count of cache hits by applications running on the platform</td>
      <td><code>perf.cache_references</code></td>
    </tr>
    <tr>
      <td><code>cache_misses</code></td>
      <td>the count of cache misses by applications running on the platform</td>
      <td><code>perf.cache_misses</code></td>
    </tr>
    <tr>
      <td><code>branch_instructions</code></td>
      <td>the count of branch instructions by applications running on the platform</td>
      <td><code>perf.branch_instructions</code></td>
    </tr>
    <tr>
      <td><code>branch_misses</code></td>
      <td>the count of branch misses by applications running on the platform</td>
      <td><code>perf.branch_misses</code></td>
    </tr>
    <tr>
      <td><code>bus_cycles</code></td>
      <td>the count of bus cycles by applications running on the platform</td>
      <td><code>perf.bus_cycles</code></td>
    </tr>
    <tr>
      <td><code>stalled_cycles_frontend</code></td>
      <td>the count of stalled CPU cycles in the frontend of the instruction
          processor pipeline by applications running on the platform</td>
      <td><code>perf.stalled_cycles_frontend</code></td>
    </tr>
    <tr>
      <td><code>stalled_cycles_backend</code></td>
      <td>the count of stalled CPU cycles in the backend of the instruction
          processor pipeline by applications running on the platform</td>
      <td><code>perf.stalled_cycles_backend</code></td>
    </tr>
    <tr>
      <td><code>ref_cpu_cycles</code></td>
      <td>the count of total CPU cycles not affected by CPU frequency scaling
         by applications running on the platform</td>
      <td><code>perf.ref_cpu_cycles</code></td>
    </tr>
    <tr>
      <td><code>cpu_clock</code></td>
      <td>the count of CPU clock time, as measured by a monotonic
          high-resolution per-CPU timer, by applications running on
          the platform</td>
      <td><code>perf.cpu_clock</code></td>
    </tr>
    <tr>
      <td><code>task_clock</code></td>
      <td>the count of task clock time, as measured by a monotonic
          high-resolution CPU timer, specific to the task that
          is run by applications running on the platform</td>
      <td><code>perf.task_clock</code></td>
    </tr>
    <tr>
      <td><code>page_faults</code></td>
      <td>the count of page faults by applications running on the
          platform. This includes minor, major, invalid and other
          types of page faults</td>
      <td><code>perf.page_faults</code></td>
    </tr>
    <tr>
      <td><code>context_switches</code></td>
      <td>the count of context switches by applications running on
          the platform</td>
      <td><code>perf.context_switches</code></td>
    </tr>
    <tr>
      <td><code>cpu_migrations</code></td>
      <td>the count of CPU migrations, that is, where the process
          moved from one logical processor to another, by
          applications running on the platform</td>
      <td><code>perf.cpu_migrations</code></td>
    </tr>
    <tr>
      <td><code>page_faults_min</code></td>
      <td>the count of minor page faults, that is, where the
          page was present in the page cache, and therefore
          the fault avoided loading it from storage, by
          applications running on the platform</td>
      <td><code>perf.page_faults_min</code></td>
    </tr>
    <tr>
      <td><code>page_faults_maj</code></td>
      <td>the count of major page faults, that is, where the
          page was not present in the page cache, and
          therefore had to be fetched from storage, by
          applications running on the platform</td>
      <td><code>perf.page_faults_maj</code></td>
    </tr>
    <tr>
      <td><code>alignment_faults</code></td>
      <td>the count of alignment faults, that is when
          the load or store is not aligned properly, by
          applications running on the platform</td>
      <td><code>perf.alignment_faults</code></td>
    </tr>
    <tr>
      <td><code>emulation_faults</code></td>
      <td>the count of emulation faults, that is when
          the kernel traps on unimplemented instrucions
          and emulates them for user space, by
          applications running on the platform</td>
      <td><code>perf.emulation_faults</code></td>
    </tr>
  </table>

    <h3><a id="elementsDevices">Devices</a></h3>

    <p>
      The final set of XML elements are all used to describe devices
      provided to the guest domain. All devices occur as children
      of the main <code>devices</code> element.
      <span class="since">Since 0.1.3</span>
    </p>

<pre>
...
&lt;devices&gt;
  &lt;emulator&gt;/usr/lib/xen/bin/qemu-dm&lt;/emulator&gt;
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><a id="elementEmulator"><code>emulator</code></a></dt>
      <dd>
        The contents of the <code>emulator</code> element specify
        the fully qualified path to the device model emulator binary.
        The <a href="formatcaps.html">capabilities XML</a> specifies
        the recommended default emulator to use for each particular
        domain type / architecture combination.
      </dd>
    </dl>

    <p>
      To help users identifying devices they care about, every
      device can have direct child <code>alias</code> element
      which then has <code>name</code> attribute where users can
      store identifier for the device. The identifier has to have
      "ua-" prefix and must be unique within the domain. Additionally, the
      identifier must consist only of the following characters:
      <code>[a-zA-Z0-9_-]</code>.
      <span class="since">Since 3.9.0</span>
    </p>

<pre>
&lt;devices&gt;
  &lt;disk type='file'&gt;
    &lt;alias name='ua-myDisk'/&gt;
  &lt;/disk&gt;
  &lt;interface type='network' trustGuestRxFilters='yes'&gt;
    &lt;alias name='ua-myNIC'/&gt;
  &lt;/interface&gt;
  ...
&lt;/devices&gt;
</pre>

    <h4><a id="elementsDisks">Hard drives, floppy disks, CDROMs</a></h4>

    <p>
      Any device that looks like a disk, be it a floppy, harddisk,
      cdrom, or paravirtualized driver is specified via the <code>disk</code>
      element.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;disk type='file' snapshot='external'&gt;
    &lt;driver name="tap" type="aio" cache="default"/&gt;
    &lt;source file='/var/lib/xen/images/fv0' startupPolicy='optional'&gt;
      &lt;seclabel relabel='no'/&gt;
    &lt;/source&gt;
    &lt;target dev='hda' bus='ide'/&gt;
    &lt;iotune&gt;
      &lt;total_bytes_sec&gt;10000000&lt;/total_bytes_sec&gt;
      &lt;read_iops_sec&gt;400000&lt;/read_iops_sec&gt;
      &lt;write_iops_sec&gt;100000&lt;/write_iops_sec&gt;
    &lt;/iotune&gt;
    &lt;boot order='2'/&gt;
    &lt;encryption type='...'&gt;
      ...
    &lt;/encryption&gt;
    &lt;shareable/&gt;
    &lt;serial&gt;
      ...
    &lt;/serial&gt;
  &lt;/disk&gt;
    ...
  &lt;disk type='network'&gt;
    &lt;driver name="qemu" type="raw" io="threads" ioeventfd="on" event_idx="off"/&gt;
    &lt;source protocol="sheepdog" name="image_name"&gt;
      &lt;host name="hostname" port="7000"/&gt;
    &lt;/source&gt;
    &lt;target dev="hdb" bus="ide"/&gt;
    &lt;boot order='1'/&gt;
    &lt;transient/&gt;
    &lt;address type='drive' controller='0' bus='1' unit='0'/&gt;
  &lt;/disk&gt;
  &lt;disk type='network'&gt;
    &lt;driver name="qemu" type="raw"/&gt;
    &lt;source protocol="rbd" name="image_name2"&gt;
      &lt;host name="hostname" port="7000"/&gt;
      &lt;snapshot name="snapname"/&gt;
      &lt;config file="/path/to/file"/&gt;
      &lt;auth username='myuser'&gt;
        &lt;secret type='ceph' usage='mypassid'/&gt;
      &lt;/auth&gt;
    &lt;/source&gt;
    &lt;target dev="hdc" bus="ide"/&gt;
  &lt;/disk&gt;
  &lt;disk type='block' device='cdrom'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;target dev='hdd' bus='ide' tray='open'/&gt;
    &lt;readonly/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='cdrom'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol="http" name="url_path"&gt;
      &lt;host name="hostname" port="80"/&gt;
    &lt;/source&gt;
    &lt;target dev='hde' bus='ide' tray='open'/&gt;
    &lt;readonly/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='cdrom'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol="https" name="url_path"&gt;
      &lt;host name="hostname" port="443"/&gt;
    &lt;/source&gt;
    &lt;target dev='hdf' bus='ide' tray='open'/&gt;
    &lt;readonly/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='cdrom'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol="ftp" name="url_path"&gt;
      &lt;host name="hostname" port="21"/&gt;
    &lt;/source&gt;
    &lt;target dev='hdg' bus='ide' tray='open'/&gt;
    &lt;readonly/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='cdrom'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol="ftps" name="url_path"&gt;
      &lt;host name="hostname" port="990"/&gt;
    &lt;/source&gt;
    &lt;target dev='hdh' bus='ide' tray='open'/&gt;
    &lt;readonly/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='cdrom'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol="tftp" name="url_path"&gt;
      &lt;host name="hostname" port="69"/&gt;
    &lt;/source&gt;
    &lt;target dev='hdi' bus='ide' tray='open'/&gt;
    &lt;readonly/&gt;
  &lt;/disk&gt;
  &lt;disk type='block' device='lun'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source dev='/dev/sda'&gt;
      &lt;reservations managed='no'&gt;
        &lt;source type='unix' path='/path/to/qemu-pr-helper' mode='client'/&gt;
      &lt;/reservations&gt;
    &lt;target dev='sda' bus='scsi'/&gt;
    &lt;address type='drive' controller='0' bus='0' target='3' unit='0'/&gt;
  &lt;/disk&gt;
  &lt;disk type='block' device='disk'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source dev='/dev/sda'/&gt;
    &lt;geometry cyls='16383' heads='16' secs='63' trans='lba'/&gt;
    &lt;blockio logical_block_size='512' physical_block_size='4096'/&gt;
    &lt;target dev='hdj' bus='ide'/&gt;
  &lt;/disk&gt;
  &lt;disk type='volume' device='disk'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source pool='blk-pool0' volume='blk-pool0-vol0'/&gt;
    &lt;target dev='hdk' bus='ide'/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='disk'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/2'&gt;
      &lt;host name='example.com' port='3260'/&gt;
      &lt;auth username='myuser'&gt;
        &lt;secret type='iscsi' usage='libvirtiscsi'/&gt;
      &lt;/auth&gt;
    &lt;/source&gt;
    &lt;target dev='vda' bus='virtio'/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='lun'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/1'&gt;
      &lt;host name='example.com' port='3260'/&gt;
      &lt;auth username='myuser'&gt;
        &lt;secret type='iscsi' usage='libvirtiscsi'/&gt;
      &lt;/auth&gt;
    &lt;/source&gt;
    &lt;target dev='sdb' bus='scsi'/&gt;
  &lt;/disk&gt;
  &lt;disk type='network' device='lun'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source protocol='iscsi' name='iqn.2013-07.com.example:iscsi-nopool/0'&gt;
      &lt;host name='example.com' port='3260'/&gt;
      &lt;initiator&gt;
        &lt;iqn name='iqn.2013-07.com.example:client'/&gt;
      &lt;/initiator&gt;
    &lt;/source&gt;
    &lt;target dev='sdb' bus='scsi'/&gt;
  &lt;/disk&gt;
  &lt;disk type='volume' device='disk'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source pool='iscsi-pool' volume='unit:0:0:1' mode='host'/&gt;
    &lt;target dev='vdb' bus='virtio'/&gt;
  &lt;/disk&gt;
  &lt;disk type='volume' device='disk'&gt;
    &lt;driver name='qemu' type='raw'/&gt;
    &lt;source pool='iscsi-pool' volume='unit:0:0:2' mode='direct'/&gt;
    &lt;target dev='vdc' bus='virtio'/&gt;
  &lt;/disk&gt;
  &lt;disk type='file' device='disk'&gt;
    &lt;driver name='qemu' type='qcow2' queues='4'/&gt;
    &lt;source file='/var/lib/libvirt/images/domain.qcow'/&gt;
    &lt;backingStore type='file'&gt;
      &lt;format type='qcow2'/&gt;
      &lt;source file='/var/lib/libvirt/images/snapshot.qcow'/&gt;
      &lt;backingStore type='block'&gt;
        &lt;format type='raw'/&gt;
        &lt;source dev='/dev/mapper/base'/&gt;
        &lt;backingStore/&gt;
      &lt;/backingStore&gt;
    &lt;/backingStore&gt;
    &lt;target dev='vdd' bus='virtio'/&gt;
  &lt;/disk&gt;
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>disk</code></dt>
      <dd>The <code>disk</code> element is the main container for
      describing disks and supports the following attributes:
        <dl>
          <dt><code>type</code></dt>
            <dd>
            Valid values are "file", "block",
            "dir" (<span class="since">since 0.7.5</span>),
            "network" (<span class="since">since 0.8.7</span>), or
            "volume" (<span class="since">since 1.0.5</span>)
            and refer to the underlying source for the disk.
            <span class="since">Since 0.0.3</span>
            </dd>
          <dt><code>device</code></dt>
            <dd>
            Indicates how the disk is to be exposed to the guest OS. Possible
            values for this attribute are "floppy", "disk", "cdrom", and "lun",
            defaulting to "disk".
            <p>
            Using "lun" (<span class="since">since 0.9.10</span>) is only
            valid when the <code>type</code> is "block" or "network" for
            <code>protocol='iscsi'</code> or when the <code>type</code>
            is "volume" when using an iSCSI source <code>pool</code>
            for <code>mode</code> "host" or as an
            <a href="http://wiki.libvirt.org/page/NPIV_in_libvirt">NPIV</a>
            virtual Host Bus Adapter (vHBA) using a Fibre Channel storage pool.
            Configured in this manner, the LUN behaves identically to "disk",
            except that generic SCSI commands from the guest are accepted
            and passed through to the physical device. Also note that
            device='lun' will only be recognized for actual raw devices,
            but never for individual partitions or LVM partitions (in those
            cases, the kernel will reject the generic SCSI commands, making
            it identical to device='disk').
            <span class="since">Since 0.1.4</span>
            </p>
            </dd>
          <dt><code>model</code></dt>
            <dd>
            Indicates the emulated device model of the disk. Typically
            this is indicated solely by the <code>bus</code> property but
            for <code>bus</code> "virtio" the model can be specified further
            with "virtio-transitional", "virtio-non-transitional", or
            "virtio". See
            <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
            for more details.
            <span class="since">Since 5.2.0</span>
            </dd>
          <dt><code>rawio</code></dt>
            <dd>
            Indicates whether the disk needs rawio capability. Valid
            settings are "yes" or "no" (default is "no"). If any one disk
            in a domain has rawio='yes', rawio capability will be enabled
            for all disks in the domain (because, in the case of QEMU, this
            capability can only be set on a per-process basis). This attribute
            is only valid when device is "lun". NB, <code>rawio</code> intends
            to confine the capability per-device, however, current QEMU
            implementation gives the domain process broader capability
            than that (per-process basis, affects all the domain disks).
            To confine the capability as much as possible for QEMU driver
            as this stage, <code>sgio</code> is recommended, it's more
            secure than <code>rawio</code>.
            <span class="since">Since 0.9.10</span>
            </dd>
          <dt><code>sgio</code></dt>
            <dd>
            If supported by the hypervisor and OS, indicates whether
            unprivileged SG_IO commands are filtered for the disk. Valid
            settings are "filtered" or "unfiltered" where the default is
            "filtered". Only available when the <code>device</code> is 'lun'.
            <span class="since">Since 1.0.2</span>
            </dd>
          <dt><code>snapshot</code></dt>
            <dd>
            Indicates the default behavior of the disk during disk snapshots:
            "<code>internal</code>" requires a file format such as qcow2 that
            can store both the snapshot and the data changes since the snapshot;
            "<code>external</code>" will separate the snapshot from the live
            data; and "<code>no</code>" means the disk will not participate in
            snapshots. Read-only disks default to "<code>no</code>", while the
            default for other disks depends on the hypervisor's capabilities.
            Some hypervisors allow a per-snapshot choice as well, during
            <a href="formatsnapshot.html">domain snapshot creation</a>.
            Not all snapshot modes are supported; for example, enabling
            snapshots with a transient disk generally does not make sense.
            <span class="since">Since 0.9.5</span>
            </dd>
        </dl>
      </dd>
      <dt><code>source</code></dt>
      <dd>Representation of the disk <code>source</code> depends on the
      disk <code>type</code> attribute value as follows:
          <dl>
            <dt><code>file</code></dt>
              <dd>
              The <code>file</code> attribute specifies the fully-qualified
              path to the file holding the disk.
              <span class="since">Since 0.0.3</span>
              </dd>
            <dt><code>block</code></dt>
              <dd>
              The <code>dev</code> attribute specifies the fully-qualified path
              to the host device to serve as the disk.
              <span class="since">Since 0.0.3</span>
              </dd>
            <dt><code>dir</code></dt>
              <dd>
              The <code>dir</code> attribute specifies the fully-qualified path
              to the directory to use as the disk.
              <span class="since">Since 0.7.5</span>
              </dd>
            <dt><code>network</code></dt>
              <dd>
              The <code>protocol</code> attribute specifies the protocol to
              access to the requested image. Possible values are "nbd",
              "iscsi", "rbd", "sheepdog", "gluster" or "vxhs".

              <p>If the <code>protocol</code> attribute is "rbd", "sheepdog",
              "gluster", or "vxhs", an additional attribute <code>name</code>
              is mandatory to specify which volume/image will be used.
              </p>

              <p>For "nbd", the <code>name</code> attribute is optional. TLS
              transport for NBD can be enabled by setting the <code>tls</code>
              attribute to <code>yes</code>. For the QEMU hypervisor, usage of
              a TLS environment can also be globally controlled on the host by
              the <code>nbd_tls</code> and <code>nbd_tls_x509_cert_dir</code> in
              /etc/libvirt/qemu.conf.
              ('tls' <span class="since">Since 4.5.0</span>)
              </p>

              <p>For "iscsi" (<span class="since">since 1.0.4</span>), the
              <code>name</code> attribute may include a logical unit number,
              separated from the target's name by a slash (e.g.,
              <code>iqn.2013-07.com.example:iscsi-pool/1</code>). If not
              specified, the default LUN is zero.
              </p>

              <p>For "vxhs" (<span class="since">since 3.8.0</span>), the
              <code>name</code> is the UUID of the volume, assigned by the
              HyperScale server. Additionally, an optional attribute
              <code>tls</code> (QEMU only) can be used to control whether a
              VxHS block device would utilize a hypervisor configured TLS
              X.509 certificate environment in order to encrypt the data
              channel. For the QEMU hypervisor, usage of a TLS environment can
              also be globally controlled on the host by the
              <code>vxhs_tls</code> and <code>vxhs_tls_x509_cert_dir</code> or
              <code>default_tls_x509_cert_dir</code> settings in the file
              /etc/libvirt/qemu.conf. If <code>vxhs_tls</code> is enabled,
              then unless the domain <code>tls</code> attribute is set to "no",
              libvirt will use the host configured TLS environment. If the
              <code>tls</code> attribute is set to "yes", then regardless of
              the qemu.conf setting, TLS authentication will be attempted.
              </p>
              <span class="since">Since 0.8.7</span>
              </dd>
            <dt><code>volume</code></dt>
              <dd>
              The underlying disk source is represented by attributes
              <code>pool</code> and <code>volume</code>. Attribute
              <code>pool</code> specifies the name of the
              <a href="formatstorage.html">storage pool</a> (managed
              by libvirt) where the disk source resides. Attribute
              <code>volume</code> specifies the name of storage volume (managed
              by libvirt) used as the disk source. The value for the
              <code>volume</code> attribute will be the output from the "Name"
              column of a <code>virsh vol-list [pool-name]</code> command.
              <p>
              Use the attribute <code>mode</code>
              (<span class="since">since 1.1.1</span>) to indicate how to
              represent the LUN as the disk source. Valid values are
              "direct" and "host". If <code>mode</code> is not specified,
              the default is to use "host".

              Using "direct" as the <code>mode</code> value indicates to use
              the <a href="formatstorage.html">storage pool's</a>
              <code>source</code> element <code>host</code> attribute as
              the disk source to generate the libiscsi URI (e.g.
              'file=iscsi://example.com:3260/iqn.2013-07.com.example:iscsi-pool/1').

              Using "host" as the <code>mode</code> value indicates to use the
              LUN's path as it shows up on host (e.g.
              'file=/dev/disk/by-path/ip-example.com:3260-iscsi-iqn.2013-07.com.example:iscsi-pool-lun-1').

              Using a LUN from an iSCSI source pool provides the same
              features as a <code>disk</code> configured using
              <code>type</code> 'block' or 'network' and <code>device</code>
              of 'lun' with respect to how the LUN is presented to and
              may be used by the guest.

              <span class="since">Since 1.0.5</span>
              </p>
              </dd>
          </dl>
        With "file", "block", and "volume", one or more optional
        sub-elements <code>seclabel</code>, <a href="#seclabel">described
        below</a> (and <span class="since">since 0.9.9</span>), can be
        used to override the domain security labeling policy for just
        that source file. (NB, for "volume" type disk, <code>seclabel</code>
        is only valid when the specified storage volume is of 'file' or
        'block' type).
        <p>
        The <code>source</code> element may also have the <code>index</code>
        attribute with same semantics the <a href='#elementsDiskBackingStoreIndex'>
        <code>index</code></a> attribute of <code>backingStore</code>
        </p>
        <p>
        The <code>source</code> element may contain the following sub elements:
        </p>

        <dl>
          <dt><code>host</code></dt>
          <dd>
            <p>
            When the disk <code>type</code> is "network", the <code>source</code>
            may have zero or more <code>host</code> sub-elements used to
            specify the hosts to connect.

            The <code>host</code> element supports 4 attributes, viz.  "name",
            "port", "transport" and "socket", which specify the hostname,
            the port number, transport type and path to socket, respectively.
            The meaning of this element and the number of the elements depend
            on the protocol attribute.
            </p>
            <table class="top_table">
              <tr>
                <th> Protocol </th>
                <th> Meaning </th>
                <th> Number of hosts </th>
                <th> Default port </th>
              </tr>
              <tr>
                <td> nbd </td>
                <td> a server running nbd-server </td>
                <td> only one </td>
                <td> 10809 </td>
              </tr>
              <tr>
                <td> iscsi </td>
                <td> an iSCSI server </td>
                <td> only one </td>
                <td> 3260 </td>
              </tr>
              <tr>
                <td> rbd </td>
                <td> monitor servers of RBD </td>
                <td> one or more </td>
                <td> librados default </td>
              </tr>
              <tr>
                <td> sheepdog </td>
                <td> one of the sheepdog servers (default is localhost:7000) </td>
                <td> zero or one </td>
                <td> 7000 </td>
              </tr>
              <tr>
                <td> gluster </td>
                <td> a server running glusterd daemon </td>
                <td> one or more (<span class="since">Since 2.1.0</span>), just one prior to that </td>
                <td> 24007 </td>
              </tr>
              <tr>
                <td> vxhs </td>
                <td> a server running Veritas HyperScale daemon </td>
                <td> only one </td>
                <td> 9999 </td>
              </tr>
            </table>
            <p>
            gluster supports "tcp", "rdma", "unix" as valid values for the
            transport attribute.  nbd supports "tcp" and "unix".  Others only
            support "tcp".  If nothing is specified, "tcp" is assumed. If the
            transport is "unix", the socket attribute specifies the path to an
            AF_UNIX socket.
            </p>
          </dd>
          <dt><code>snapshot</code></dt>
          <dd>
            The <code>name</code> attribute of <code>snapshot</code> element can
            optionally specify an internal snapshot name to be used as the
            source for storage protocols.
            Supported for 'rbd' <span class="since">since 1.2.11 (QEMU only).</span>
          </dd>
          <dt><code>config</code></dt>
          <dd>
            The <code>file</code> attribute for the <code>config</code> element
            provides a fully qualified path to a configuration file to be
            provided as a parameter to the client of a networked storage
            protocol. Supported for 'rbd' <span class="since">since 1.2.11
            (QEMU only).</span>
          </dd>
          <dt><code>auth</code></dt>
          <dd><span class="since">Since libvirt 3.9.0</span>, the
            <code>auth</code> element is supported for a disk
            <code>type</code> "network" that is using a <code>source</code>
            element with the <code>protocol</code> attributes "rbd" or "iscsi".
            If present, the <code>auth</code> element provides the
            authentication credentials needed to access the source.  It
            includes a mandatory attribute <code>username</code>, which
            identifies the username to use during authentication, as well
            as a sub-element <code>secret</code> with mandatory
            attribute <code>type</code>, to tie back to
            a <a href="formatsecret.html">libvirt secret object</a> that
            holds the actual password or other credentials (the domain XML
            intentionally does not expose the password, only the reference
            to the object that does manage the password).
            Known secret types are "ceph" for Ceph RBD network sources and
            "iscsi" for CHAP authentication of iSCSI targets.
            Both will require either a <code>uuid</code> attribute
            with the UUID of the secret object or a <code>usage</code>
            attribute matching the key that was specified in the
            secret object.
          </dd>
          <dt><code>encryption</code></dt>
          <dd><span class="since">Since libvirt 3.9.0</span>, the
            <code>encryption</code> can be a sub-element of the
            <code>source</code> element for encrypted storage sources.
            If present, specifies how the storage source is encrypted
            See the
            <a href="formatstorageencryption.html">Storage Encryption</a>
            page for more information.
            <p/>
            Note that the 'qcow' format of encryption is broken and thus is no
            longer supported for use with disk images.
            (<span class="since">Since libvirt 4.5.0</span>)
          </dd>
          <dt><code>reservations</code></dt>
          <dd><span class="since">Since libvirt 4.4.0</span>, the
            <code>reservations</code> can be a sub-element of the
            <code>source</code> element for storage sources (QEMU driver only).
            If present it enables persistent reservations for SCSI
            based disks. The element has one mandatory attribute
            <code>managed</code> with accepted values <code>yes</code> and
            <code>no</code>. If <code>managed</code> is enabled libvirt prepares
            and manages any resources needed. When the persistent reservations
            are unmanaged, then the hypervisor acts as a client and the path to
            the server socket must be provided in the child element
            <code>source</code>, which currently accepts only the following
            attributes:
            <code>type</code> with one value <code>unix</code>,
            <code>path</code> path to the socket, and
            finally <code>mode</code> which accepts one value
            <code>client</code> specifying the role of hypervisor.
            It's recommended to allow libvirt manage the persistent
            reservations.
          </dd>
          <dt><code>initiator</code></dt>
          <dd><span class="since">Since libvirt 4.7.0</span>, the
            <code>initiator</code> element is supported for a disk
            <code>type</code> "network" that is using a <code>source</code>
            element with the <code>protocol</code> attribute "iscsi".
            If present, the <code>initiator</code> element provides the
            initiator IQN needed to access the source via mandatory
            attribute <code>name</code>.
          </dd>
        </dl>

        <p>
        For a "file" or "volume" disk type which represents a cdrom or floppy
        (the <code>device</code> attribute), it is possible to define
        policy what to do with the disk if the source file is not accessible.
        (NB, <code>startupPolicy</code> is not valid for "volume" disk unless
         the specified storage volume is of "file" type). This is done by the
        <code>startupPolicy</code> attribute
        (<span class="since">since 0.9.7</span>),
        accepting these values:
        </p>
        <table class="top_table">
          <tr>
            <td> mandatory </td>
            <td> fail if missing for any reason (the default) </td>
          </tr>
          <tr>
            <td> requisite </td>
            <td> fail if missing on boot up,
                 drop if missing on migrate/restore/revert </td>
          </tr>
          <tr>
            <td> optional </td>
            <td> drop if missing at any start attempt </td>
          </tr>
        </table>
        <p>
        <span class="since">Since 1.1.2</span> the <code>startupPolicy</code>
        is extended to support hard disks besides cdrom and floppy. On guest
        cold bootup, if a certain disk is not accessible or its disk chain is
        broken, with startupPolicy 'optional' the guest will drop this disk.
        This feature doesn't support migration currently.
        </p>
        </dd>
      <dt><code>backingStore</code></dt>
      <dd>
        This element describes the backing store used by the disk
        specified by sibling <code>source</code> element. It is
        currently ignored on input and only used for output to
        describe the detected backing chains of running
        domains <span class="since">since 1.2.4</span> (although a
        future version of libvirt may start accepting chains on input,
        or output information for offline domains). An
        empty <code>backingStore</code> element means the sibling
        source is self-contained and is not based on any backing
        store. For backing chain information to be accurate, the
        backing format must be correctly specified in the metadata of
        each file of the chain (files created by libvirt satisfy this
        property, but using existing external files for snapshot or
        block copy operations requires the end user to pre-create the
        file correctly). The following attributes are
        supported in <code>backingStore</code>:
        <dl>
          <dt><code>type</code></dt>
          <dd>
            The <code>type</code> attribute represents the type of disk used
            by the backing store, see disk type attribute above for more
            details and possible values.
          </dd>
          <dt><code><a id="elementsDiskBackingStoreIndex">index</a></code></dt>
          <dd>
            This attribute is only valid in output (and ignored on input) and
            it can be used to refer to a specific part of the disk chain when
            doing block operations (such as via the
            <code>virDomainBlockRebase</code> API). For example,
            <code>vda[2]</code> refers to the backing store with
            <code>index='2'</code> of the disk with <code>vda</code> target.
          </dd>
        </dl>
        Moreover, <code>backingStore</code> supports the following sub-elements:
        <dl>
          <dt><code>format</code></dt>
          <dd>
            The <code>format</code> element contains <code>type</code>
            attribute which specifies the internal format of the backing
            store, such as <code>raw</code> or <code>qcow2</code>.
          </dd>
          <dt><code>source</code></dt>
          <dd>
            This element has the same structure as the <code>source</code>
            element in <code>disk</code>. It specifies which file, device,
            or network location contains the data of the described backing
            store.
          </dd>
          <dt><code>backingStore</code></dt>
          <dd>
            If the backing store is not self-contained, the next element
            in the chain is described by nested <code>backingStore</code>
            element.
          </dd>
        </dl>
      </dd>
      <dt><code>mirror</code></dt>
      <dd>
        This element is present if the hypervisor has started a
        long-running block job operation, where the mirror location in
        the <code>source</code> sub-element will eventually have the
        same contents as the source, and with the file format in the
        sub-element <code>format</code> (which might differ from the
        format of the source).  The details of the <code>source</code>
        sub-element are determined by the <code>type</code> attribute
        of the mirror, similar to what is done for the
        overall <code>disk</code> device element. The <code>job</code>
        attribute mentions which API started the operation ("copy" for
        the <code>virDomainBlockRebase</code> API, or "active-commit"
        for the <code>virDomainBlockCommit</code>
        API), <span class="since">since 1.2.7</span>.  The
        attribute <code>ready</code>, if present, tracks progress of
        the job: <code>yes</code> if the disk is known to be ready to
        pivot, or, <span class="since">since
        1.2.7</span>, <code>abort</code> or <code>pivot</code> if the
        job is in the process of completing.  If <code>ready</code> is
        not present, the disk is probably still
        copying.  For now, this element only valid in output; it is
        ignored on input.  The <code>source</code> sub-element exists
        for all two-phase jobs <span class="since">since 1.2.6</span>.
        Older libvirt supported only block copy to a
        file, <span class="since">since 0.9.12</span>; for
        compatibility with older clients, such jobs include redundant
        information in the attributes <code>file</code>
        and <code>format</code> in the <code>mirror</code> element.
      </dd>
      <dt><code>target</code></dt>
      <dd>The <code>target</code> element controls the bus / device
        under which the disk is exposed to the guest
        OS. The <code>dev</code> attribute indicates the "logical"
        device name. The actual device name specified is not
        guaranteed to map to the device name in the guest OS. Treat it
        as a device ordering hint.  The optional <code>bus</code>
        attribute specifies the type of disk device to emulate;
        possible values are driver specific, with typical values being
        "ide", "scsi", "virtio", "xen", "usb", "sata", or
        "sd" <span class="since">"sd" since 1.1.2</span>. If omitted, the bus
        type is inferred from the style of the device name (e.g. a device named
        'sda' will typically be exported using a SCSI bus). The optional
        attribute <code>tray</code> indicates the tray status of the
        removable disks (i.e. CDROM or Floppy disk), the value can be either
        "open" or "closed", defaults to "closed". NB, the value of
        <code>tray</code> could be updated while the domain is running.
        The optional attribute <code>removable</code> sets the
        removable flag for USB disks, and its value can be either "on"
        or "off", defaulting to "off". <span class="since">Since
        0.0.3; <code>bus</code> attribute since 0.4.3;
        <code>tray</code> attribute since 0.9.11; "usb" attribute value since
        after 0.4.4; "sata" attribute value since 0.9.7; "removable" attribute
        value since 1.1.3</span>
      </dd>
      <dt><code>iotune</code></dt>
      <dd>The optional <code>iotune</code> element provides the
        ability to provide additional per-device I/O tuning, with
        values that can vary for each device (contrast this to
        the <a href="#elementsBlockTuning"><code>&lt;blkiotune&gt;</code></a>
        element, which applies globally to the domain).  Currently,
        the only tuning available is Block I/O throttling for qemu.
        This element has optional sub-elements; any sub-element not
        specified or given with a value of 0 implies no
        limit.  <span class="since">Since 0.9.8</span>
        <dl>
          <dt><code>total_bytes_sec</code></dt>
          <dd>The optional <code>total_bytes_sec</code> element is the
            total throughput limit in bytes per second.  This cannot
            appear with <code>read_bytes_sec</code>
            or <code>write_bytes_sec</code>.</dd>
          <dt><code>read_bytes_sec</code></dt>
          <dd>The optional <code>read_bytes_sec</code> element is the
            read throughput limit in bytes per second.</dd>
          <dt><code>write_bytes_sec</code></dt>
          <dd>The optional <code>write_bytes_sec</code> element is the
            write throughput limit in bytes per second.</dd>
          <dt><code>total_iops_sec</code></dt>
          <dd>The optional <code>total_iops_sec</code> element is the
            total I/O operations per second.  This cannot
            appear with <code>read_iops_sec</code>
            or <code>write_iops_sec</code>.</dd>
          <dt><code>read_iops_sec</code></dt>
          <dd>The optional <code>read_iops_sec</code> element is the
            read I/O operations per second.</dd>
          <dt><code>write_iops_sec</code></dt>
          <dd>The optional <code>write_iops_sec</code> element is the
            write I/O operations per second.</dd>
          <dt><code>total_bytes_sec_max</code></dt>
          <dd>The optional <code>total_bytes_sec_max</code> element is the
            maximum total throughput limit in bytes per second.  This cannot
            appear with <code>read_bytes_sec_max</code>
            or <code>write_bytes_sec_max</code>.</dd>
          <dt><code>read_bytes_sec_max</code></dt>
          <dd>The optional <code>read_bytes_sec_max</code> element is the
            maximum read throughput limit in bytes per second.</dd>
          <dt><code>write_bytes_sec_max</code></dt>
          <dd>The optional <code>write_bytes_sec_max</code> element is the
            maximum write throughput limit in bytes per second.</dd>
          <dt><code>total_iops_sec_max</code></dt>
          <dd>The optional <code>total_iops_sec_max</code> element is the
            maximum total I/O operations per second.  This cannot
            appear with <code>read_iops_sec_max</code>
            or <code>write_iops_sec_max</code>.</dd>
          <dt><code>read_iops_sec_max</code></dt>
          <dd>The optional <code>read_iops_sec_max</code> element is the
            maximum read I/O operations per second.</dd>
          <dt><code>write_iops_sec_max</code></dt>
          <dd>The optional <code>write_iops_sec_max</code> element is the
            maximum write I/O operations per second.</dd>
          <dt><code>size_iops_sec</code></dt>
          <dd>The optional <code>size_iops_sec</code> element is the
            size of I/O operations per second.
          <p>
            <span class="since">Throughput limits since 1.2.11 and QEMU 1.7</span>
          </p>
          </dd>
          <dt><code>group_name</code></dt>
          <dd>The optional <code>group_name</code> provides the cability
            to share I/O throttling quota between multiple drives. This
            prevents end-users from circumventing a hosting provider's
            throttling policy by splitting 1 large drive in N small drives
            and getting N times the normal throttling quota. Any name may
            be used.
          <p>
            <span class="since">group_name since 3.0.0 and QEMU 2.4</span>
          </p>
          </dd>
          <dt><code>total_bytes_sec_max_length</code></dt>
          <dd>The optional <code>total_bytes_sec_max_length</code>
            element is the maximum duration in seconds for the
            <code>total_bytes_sec_max</code> burst period. Only valid
            when the <code>total_bytes_sec_max</code> is set.</dd>
          <dt><code>read_bytes_sec_max_length</code></dt>
          <dd>The optional <code>read_bytes_sec_max_length</code>
            element is the maximum duration in seconds for the
            <code>read_bytes_sec_max</code> burst period. Only valid
            when the <code>read_bytes_sec_max</code> is set.</dd>
          <dt><code>write_bytes_sec_max</code></dt>
          <dd>The optional <code>write_bytes_sec_max_length</code>
            element is the maximum duration in seconds for the
            <code>write_bytes_sec_max</code> burst period. Only valid
            when the <code>write_bytes_sec_max</code> is set.</dd>
          <dt><code>total_iops_sec_max_length</code></dt>
          <dd>The optional <code>total_iops_sec_max_length</code>
            element is the maximum duration in seconds for the
            <code>total_iops_sec_max</code> burst period. Only valid
            when the <code>total_iops_sec_max</code> is set.</dd>
          <dt><code>read_iops_sec_max_length</code></dt>
          <dd>The optional <code>read_iops_sec_max_length</code>
            element is the maximum duration in seconds for the
            <code>read_iops_sec_max</code> burst period. Only valid
            when the <code>read_iops_sec_max</code> is set.</dd>
          <dt><code>write_iops_sec_max</code></dt>
          <dd>The optional <code>write_iops_sec_max_length</code>
            element is the maximum duration in seconds for the
            <code>write_iops_sec_max</code> burst period. Only valid
            when the <code>write_iops_sec_max</code> is set.
          <p>
            <span class="since">Throughput length since 2.4.0 and QEMU 2.6</span>
          </p>
          </dd>
        </dl>
      </dd>
      <dt><code>driver</code></dt>
      <dd>
        The optional driver element allows specifying further details
        related to the hypervisor driver used to provide the disk.
        <span class="since">Since 0.1.8</span>
        <ul>
          <li>
            If the hypervisor supports multiple backend drivers, then
            the <code>name</code> attribute selects the primary
            backend driver name, while the optional <code>type</code>
            attribute provides the sub-type.  For example, xen
            supports a name of "tap", "tap2", "phy", or "file", with a
            type of "aio", while qemu only supports a name of "qemu",
            but multiple types including "raw", "bochs", "qcow2", and
            "qed".
          </li>
          <li>
            The optional <code>cache</code> attribute controls the
            cache mechanism, possible values are "default", "none",
            "writethrough", "writeback", "directsync" (like
            "writethrough", but it bypasses the host page cache) and
            "unsafe" (host may cache all disk io, and sync requests from
            guest are ignored).
            <span class="since">
              Since 0.6.0,
              "directsync" since 0.9.5,
              "unsafe" since 0.9.7
            </span>
          </li>
          <li>
            The optional <code>error_policy</code> attribute controls
            how the hypervisor will behave on a disk read or write
            error, possible values are "stop", "report", "ignore", and
            "enospace".<span class="since">Since 0.8.0, "report" since
            0.9.7</span> The default is left to the discretion of the
            hypervisor. There is also an
            optional <code>rerror_policy</code> that controls behavior
            for read errors only. <span class="since">Since
            0.9.7</span>. If no rerror_policy is given, error_policy
            is used for both read and write errors. If rerror_policy
            is given, it overrides the <code>error_policy</code> for
            read errors. Also note that "enospace" is not a valid
            policy for read errors, so if <code>error_policy</code> is
            set to "enospace" and no <code>rerror_policy</code> is
            given, the read error policy will be left at its default.
          </li>
          <li>
            The optional <code>io</code> attribute controls specific
            policies on I/O; qemu guests support "threads" and
            "native". <span class="since">Since 0.8.8</span>
          </li>
          <li>
            The optional <code>ioeventfd</code> attribute allows users to
            set <a href='https://patchwork.kernel.org/patch/43390/'>
            domain I/O asynchronous handling</a> for disk device.
            The default is left to the discretion of the hypervisor.
            Accepted values are "on" and "off". Enabling this allows
            qemu to execute VM while a separate thread handles I/O.
            Typically guests experiencing high system CPU utilization
            during I/O will benefit from this. On the other hand,
            on overloaded host it could increase guest I/O latency.
            <span class="since">Since 0.9.3 (QEMU and KVM only)</span>
            <b>In general you should leave this option alone, unless you
            are very certain you know what you are doing.</b>
          </li>
          <li>
            The optional <code>event_idx</code> attribute controls
            some aspects of device event processing. The value can be
            either 'on' or 'off' - if it is on, it will reduce the
            number of interrupts and exits for the guest. The default
            is determined by QEMU; usually if the feature is
            supported, default is on. In case there is a situation
            where this behavior is suboptimal, this attribute provides
            a way to force the feature off.
            <span class="since">Since 0.9.5 (QEMU and KVM only)</span>
            <b>In general you should leave this option alone, unless you
            are very certain you know what you are doing.</b>
          </li>
          <li>
            The optional <code>copy_on_read</code> attribute controls
            whether to copy read backing file into the image file. The
            value can be either "on" or "off".
            Copy-on-read avoids accessing the same backing file sectors
            repeatedly and is useful when the backing file is over a slow
            network. By default copy-on-read is off.
            <span class='since'>Since 0.9.10 (QEMU and KVM only)</span>
          </li>
          <li>
            The optional <code>discard</code> attribute controls whether
            discard requests (also known as "trim" or "unmap") are
            ignored or passed to the filesystem. The value can be either
            "unmap" (allow the discard request to be passed) or "ignore"
            (ignore the discard request).
            <span class='since'>Since 1.0.6 (QEMU and KVM only)</span>
          </li>
          <li>
            The optional <code>detect_zeroes</code> attribute controls whether
            to detect zero write requests.  The value can be "off", "on" or
            "unmap".  First two values turn the detection off and on,
            respectively.  The third value ("unmap") turns the detection on
            and additionally tries to discard such areas from the image based
            on the value of <code>discard</code> above (it will act as "on"
            if <code>discard</code> is set to "ignore").  NB enabling the
            detection is a compute intensive operation, but can save file
            space and/or time on slow media.
            <span class='since'>Since 2.0.0</span>
          </li>
          <li>
            The optional <code>iothread</code> attribute assigns the
            disk to an IOThread as defined by the range for the domain
            <a href="#elementsIOThreadsAllocation"><code>iothreads</code></a>
            value. Multiple disks may be assigned to the same IOThread and
            are numbered from 1 to the domain iothreads value. Available
            for a disk device <code>target</code> configured to use "virtio"
            <code>bus</code> and "pci" or "ccw" <code>address</code> types.
            <span class='since'>Since 1.2.8 (QEMU 2.1)</span>
          </li>
          <li>
            The optional <code>queues</code> attribute specifies the number of
            virt queues for virtio-blk. (<span class="since">Since 3.9.0</span>)
          </li>
          <li>
          For virtio disks,
          <a href="#elementsVirtio">Virtio-specific options</a> can also be
          set. (<span class="since">Since 3.5.0</span>)
          </li>
        </ul>
      </dd>
      <dt><code>backenddomain</code></dt>
      <dd>The optional <code>backenddomain</code> element allows specifying a
          backend domain (aka driver domain) hosting the disk.  Use the
          <code>name</code> attribute to specify the backend domain name.
          <span class="since">Since 1.2.13 (Xen only)</span>
      </dd>
      <dt><code>boot</code></dt>
      <dd>Specifies that the disk is bootable. The <code>order</code>
        attribute determines the order in which devices will be tried during
        boot sequence. On the S390 architecture only the first boot device is
        used. The optional <code>loadparm</code> attribute is an 8 character
        string which can be queried by guests on S390 via sclp or diag 308.
        Linux guests on S390 can use <code>loadparm</code> to select a boot
        entry. <span class="since">Since 3.5.0</span>
        The per-device <code>boot</code> elements cannot be used together
        with general boot elements in
        <a href="#elementsOSBIOS">BIOS bootloader</a> section.
        <span class="since">Since 0.8.8</span>
      </dd>
      <dt><code>encryption</code></dt>
      <dd>Starting with <span class="since">libvirt 3.9.0</span> the
        <code>encryption</code> element is preferred to be a sub-element
        of the <code>source</code> element. If present, specifies how the
        volume is encrypted using "qcow". See the
        <a href="formatstorageencryption.html">Storage Encryption</a> page
        for more information.
      </dd>
      <dt><code>readonly</code></dt>
      <dd>If present, this indicates the device cannot be modified by
        the guest.  For now, this is the default for disks with
        attribute <code>device='cdrom'</code>.
      </dd>
      <dt><code>shareable</code></dt>
      <dd>If present, this indicates the device is expected to be shared
          between domains (assuming the hypervisor and OS support this),
          which means that caching should be deactivated for that device.
      </dd>
      <dt><code>transient</code></dt>
      <dd>If present, this indicates that changes to the device
        contents should be reverted automatically when the guest
        exits.  With some hypervisors, marking a disk transient
        prevents the domain from participating in migration or
        snapshots. <span class="since">Since 0.9.5</span>
      </dd>
      <dt><code>serial</code></dt>
      <dd>If present, this specify serial number of virtual hard drive.
          For example, it may look
          like <code>&lt;serial&gt;WD-WMAP9A966149&lt;/serial&gt;</code>.
          Not supported for scsi-block devices, that is those using
          disk <code>type</code> 'block' using <code>device</code> 'lun'
          on <code>bus</code> 'scsi'.
          <span class="since">Since 0.7.1</span>
      </dd>
      <dt><code>wwn</code></dt>
      <dd>If present, this element specifies the WWN (World Wide Name)
        of a virtual hard disk or CD-ROM drive. It must be composed
        of 16 hexadecimal digits.
        <span class='since'>Since 0.10.1</span>
      </dd>
      <dt><code>vendor</code></dt>
      <dd>If present, this element specifies the vendor of a virtual hard
        disk or CD-ROM device. It must not be longer than 8 printable
        characters.
        <span class='since'>Since 1.0.1</span>
      </dd>
      <dt><code>product</code></dt>
      <dd>If present, this element specifies the product of a virtual hard
        disk or CD-ROM device. It must not be longer than 16 printable
        characters.
        <span class='since'>Since 1.0.1</span>
      </dd>
      <dt><code>address</code></dt>
      <dd>If present, the <code>address</code> element ties the disk
        to a given slot of a controller (the
        actual <code>&lt;controller&gt;</code> device can often be
        inferred by libvirt, although it can
        be <a href="#elementsControllers">explicitly specified</a>).
        The <code>type</code> attribute is mandatory, and is typically
        "pci" or "drive".  For a "pci" controller, additional
        attributes for <code>bus</code>, <code>slot</code>,
        and <code>function</code> must be present, as well as
        optional <code>domain</code> and <code>multifunction</code>.
        Multifunction defaults to 'off'; any other value requires
        QEMU 0.1.3 and <span class="since">libvirt 0.9.7</span>.  For a
        "drive" controller, additional attributes
        <code>controller</code>, <code>bus</code>, <code>target</code>
        (<span class="since">libvirt 0.9.11</span>), and <code>unit</code>
        are available, each defaulting to 0.
      </dd>
      <dt><code>auth</code></dt>
      <dd>Starting with <span class="since">libvirt 3.9.0</span> the
        <code>auth</code> element is preferred to be a sub-element of
        the <code>source</code> element. The element is still read and
        managed as a <code>disk</code> sub-element. It is invalid to use
        <code>auth</code> as both a sub-element of <code>disk</code>
        and <code>source</code>. The <code>auth</code> element was
        introduced as a <code>disk</code> sub-element in
        <span class="since">libvirt 0.9.7.</span>
      </dd>
      <dt><code>geometry</code></dt>
      <dd>The optional <code>geometry</code> element provides the
        ability to override geometry settings. This mostly useful for
        S390 DASD-disks or older DOS-disks.  <span class="since">0.10.0</span>
        <dl>
          <dt><code>cyls</code></dt>
          <dd>The <code>cyls</code> attribute is the
            number of cylinders. </dd>
          <dt><code>heads</code></dt>
          <dd>The <code>heads</code> attribute is the
            number of heads. </dd>
          <dt><code>secs</code></dt>
          <dd>The <code>secs</code> attribute is the
            number of sectors per track. </dd>
          <dt><code>trans</code></dt>
          <dd>The optional <code>trans</code> attribute is the
            BIOS-Translation-Modus (none, lba or auto)</dd>
        </dl>
      </dd>
      <dt><code>blockio</code></dt>
      <dd>If present, the <code>blockio</code> element allows
        to override any of the block device properties listed below.
        <span class="since">Since 0.10.2 (QEMU and KVM)</span>
        <dl>
          <dt><code>logical_block_size</code></dt>
          <dd>The logical block size the disk will report to the guest
            OS. For Linux this would be the value returned by the
            BLKSSZGET ioctl and describes the smallest units for disk
            I/O.
          </dd>
          <dt><code>physical_block_size</code></dt>
          <dd>The physical block size the disk will report to the guest
            OS. For Linux this would be the value returned by the
            BLKPBSZGET ioctl and describes the disk's hardware sector
            size which can be relevant for the alignment of disk data.
          </dd>
        </dl>
      </dd>
    </dl>

    <h4><a id="elementsFilesystems">Filesystems</a></h4>

    <p>
      A directory on the host that can be accessed directly from the guest.
      <span class="since">since 0.3.3, since 0.8.5 for QEMU/KVM</span>
    </p>

<pre>
...
&lt;devices&gt;
  &lt;filesystem type='template'&gt;
    &lt;source name='my-vm-template'/&gt;
    &lt;target dir='/'/&gt;
  &lt;/filesystem&gt;
  &lt;filesystem type='mount' accessmode='passthrough'&gt;
    &lt;driver type='path' wrpolicy='immediate'/&gt;
    &lt;source dir='/export/to/guest'/&gt;
    &lt;target dir='/import/from/host'/&gt;
    &lt;readonly/&gt;
  &lt;/filesystem&gt;
  &lt;filesystem type='file' accessmode='passthrough'&gt;
    &lt;driver name='loop' type='raw'/&gt;
    &lt;driver type='path' wrpolicy='immediate'/&gt;
    &lt;source file='/export/to/guest.img'/&gt;
    &lt;target dir='/import/from/host'/&gt;
    &lt;readonly/&gt;
  &lt;/filesystem&gt;
  ...
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>filesystem</code></dt>
      <dd>

      The filesystem attribute <code>type</code> specifies the type of the
      <code>source</code>. The possible values are:

        <dl>
        <dt><code>mount</code></dt>
        <dd>
        A host directory to mount in the guest. Used by LXC,
        OpenVZ <span class="since">(since 0.6.2)</span>
        and QEMU/KVM <span class="since">(since 0.8.5)</span>.
        This is the default <code>type</code> if one is not specified.
        This mode also has an optional
        sub-element <code>driver</code>, with an
        attribute <code>type='path'</code>
        or <code>type='handle'</code> <span class="since">(since
        0.9.7)</span>. The driver block has an optional attribute
        <code>wrpolicy</code> that further controls interaction with
        the host page cache; omitting the attribute gives default behavior,
        while the value <code>immediate</code> means that a host writeback
        is immediately triggered for all pages touched during a guest file
        write operation <span class="since">(since 0.9.10)</span>.
        </dd>
        <dt><code>template</code></dt>
        <dd>
        OpenVZ filesystem template. Only used by OpenVZ driver.
        </dd>
        <dt><code>file</code></dt>
        <dd>
        A host file will be treated as an image and mounted in
        the guest. The filesystem format will be autodetected.
        Only used by LXC driver.
        </dd>
        <dt><code>block</code></dt>
        <dd>
        A host block device to mount in the guest. The filesystem
        format will be autodetected. Only used by LXC driver
        <span class="since">(since 0.9.5)</span>.
        </dd>
        <dt><code>ram</code></dt>
        <dd>
          An in-memory filesystem, using memory from the host OS.
          The source element has a single attribute <code>usage</code>
          which gives the memory usage limit in KiB, unless units
          are specified by the <code>units</code> attribute. Only used
          by LXC driver.
          <span class="since"> (since 0.9.13)</span></dd>
        <dt><code>bind</code></dt>
        <dd>
          A directory inside the guest will be bound to another
          directory inside the guest. Only used by LXC driver
          <span class="since"> (since 0.9.13)</span></dd>
        </dl>

      The filesystem block has an optional attribute <code>accessmode</code>
      which specifies the security mode for accessing the source
      <span class="since">(since 0.8.5)</span>. Currently this only works
      with <code>type='mount'</code> for the QEMU/KVM driver. The possible
      values are:

        <dl>
        <dt><code>passthrough</code></dt>
        <dd>
        The <code>source</code> is accessed with the permissions of the
        user inside the guest. This is the default <code>accessmode</code> if
        one is not specified.
        <a href="http://lists.gnu.org/archive/html/qemu-devel/2010-05/msg02673.html">More info</a>
        </dd>
        <dt><code>mapped</code></dt>
        <dd>
        The <code>source</code> is accessed with the permissions of the
        hypervisor (QEMU process).
        <a href="http://lists.gnu.org/archive/html/qemu-devel/2010-05/msg02673.html">More info</a>
        </dd>
        <dt><code>squash</code></dt>
        <dd>
        Similar to 'passthrough', the exception is that failure of
        privileged operations like 'chown' are ignored. This makes a
        passthrough-like mode usable for people who run the hypervisor
        as non-root.
        <a href="http://lists.gnu.org/archive/html/qemu-devel/2010-09/msg00121.html">More info</a>
        </dd>
        </dl>

      <span class="since">Since 5.2.0</span>, the filesystem element
      has an optional attribute <code>model</code> with supported values
      "virtio-transitional", "virtio-non-transitional", or "virtio".
      See <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
      for more details.
      </dd>

      <dt><code>driver</code></dt>
      <dd>
        The optional driver element allows specifying further details
        related to the hypervisor driver used to provide the filesystem.
        <span class="since">Since 1.0.6</span>
        <ul>
          <li>
            If the hypervisor supports multiple backend drivers, then
            the <code>type</code> attribute selects the primary
            backend driver name, while the <code>format</code>
            attribute provides the format type. For example, LXC
            supports a type of "loop", with a format of "raw" or
            "nbd" with any format. QEMU supports a type of "path"
            or "handle", but no formats. Virtuozzo driver supports
            a type of "ploop" with a format of "ploop".
          </li>
          <li>
          For virtio-backed devices,
          <a href="#elementsVirtio">Virtio-specific options</a> can also be
          set. (<span class="since">Since 3.5.0</span>)
          </li>
        </ul>
      </dd>

      <dt><code>source</code></dt>
      <dd>
        The resource on the host that is being accessed in the guest. The
        <code>name</code> attribute must be used with
        <code>type='template'</code>, and the <code>dir</code> attribute must
        be used with <code>type='mount'</code>. The <code>usage</code> attribute
        is used with <code>type='ram'</code> to set the memory limit in KiB,
        unless units are specified by the <code>units</code> attribute.
      </dd>

      <dt><code>target</code></dt>
      <dd>
        Where the <code>source</code> can be accessed in the guest. For
        most drivers this is an automatic mount point, but for QEMU/KVM
        this is merely an arbitrary string tag that is exported to the
        guest as a hint for where to mount.
      </dd>

      <dt><code>readonly</code></dt>
      <dd>
        Enables exporting filesystem as a readonly mount for guest, by
        default read-write access is given (currently only works for
        QEMU/KVM driver).
      </dd>

      <dt><code>space_hard_limit</code></dt>
      <dd>
        Maximum space available to this guest's filesystem.
        <span class="since">Since 0.9.13</span>
      </dd>

      <dt><code>space_soft_limit</code></dt>
      <dd>
        Maximum space available to this guest's filesystem. The container is
        permitted to exceed its soft limits for a grace period of time. Afterwards the
        hard limit is enforced.
        <span class="since">Since 0.9.13</span>
      </dd>
    </dl>

    <h4><a id="elementsAddress">Device Addresses</a></h4>

    <p>
      Many devices have an optional <code>&lt;address&gt;</code>
      sub-element to describe where the device is placed on the
      virtual bus presented to the guest.  If an address (or any
      optional attribute within an address) is omitted on
      input, libvirt will generate an appropriate address; but an
      explicit address is required if more control over layout is
      required.  See below for device examples including an address
      element.
    </p>

    <p>
      Every address has a mandatory attribute <code>type</code> that
      describes which bus the device is on.  The choice of which
      address to use for a given device is constrained in part by the
      device and the architecture of the guest.  For example,
      a <code>&lt;disk&gt;</code> device
      uses <code>type='drive'</code>, while
      a <code>&lt;console&gt;</code> device would
      use <code>type='pci'</code> on i686 or x86_64 guests,
      or <code>type='spapr-vio'</code> on PowerPC64 pseries guests.
      Each address type has further optional attributes that control
      where on the bus the device will be placed:
    </p>

    <dl>
      <dt><code>pci</code></dt>
      <dd>PCI addresses have the following additional
        attributes: <code>domain</code> (a 2-byte hex integer, not
        currently used by qemu), <code>bus</code> (a hex value between
        0 and 0xff, inclusive), <code>slot</code> (a hex value between
        0x0 and 0x1f, inclusive), and <code>function</code> (a value
        between 0 and 7, inclusive).  Also available is
        the <code>multifunction</code> attribute, which controls
        turning on the multifunction bit for a particular
        slot/function in the PCI control register
        (<span class="since">since 0.9.7, requires QEMU
        0.13</span>). <code>multifunction</code> defaults to 'off',
        but should be set to 'on' for function 0 of a slot that will
        have multiple functions used.
        (<span class="since">Since 4.10.0</span>), PCI address extensions
        depending on the architecture are supported. For example, PCI
        addresses for S390 guests will have a <code>zpci</code> child
        element, with two attributes: <code>uid</code> (a hex value
        between 0x0001 and 0xffff, inclusive), and <code>fid</code> (a
        hex value between 0x00000000 and 0xffffffff, inclusive) used by
        PCI devices on S390 for User-defined Identifiers and Function
        Identifiers.<br/>
        <span class="since">Since 1.3.5</span>, some hypervisor
        drivers may accept an <code>&lt;address type='pci'/&gt;</code>
        element with no other attributes as an explicit request to
        assign a PCI address for the device rather than some other
        type of address that may also be appropriate for that same
        device (e.g. virtio-mmio).
      </dd>
      <dt><code>drive</code></dt>
      <dd>Drive addresses have the following additional
        attributes: <code>controller</code> (a 2-digit controller
        number), <code>bus</code> (a 2-digit bus number),
        <code>target</code> (a 2-digit target number),
        and <code>unit</code> (a 2-digit unit number on the bus).
      </dd>
      <dt><code>virtio-serial</code></dt>
      <dd>Each virtio-serial address has the following additional
        attributes: <code>controller</code> (a 2-digit controller
        number), <code>bus</code> (a 2-digit bus number),
        and <code>slot</code> (a 2-digit slot within the bus).
      </dd>
      <dt><code>ccid</code></dt>
      <dd>A CCID address, for smart-cards, has the following
        additional attributes: <code>bus</code> (a 2-digit bus
        number), and <code>slot</code> attribute (a 2-digit slot
        within the bus).  <span class="since">Since 0.8.8.</span>
      </dd>
      <dt><code>usb</code></dt>
      <dd>USB addresses have the following additional
        attributes: <code>bus</code> (a hex value between 0 and 0xfff,
        inclusive), and <code>port</code> (a dotted notation of up to
        four octets, such as 1.2 or 2.1.3.1).
      </dd>
      <dt><code>spapr-vio</code></dt>
      <dd>On PowerPC pseries guests, devices can be assigned to the
        SPAPR-VIO bus.  It has a flat 32-bit address space; by
        convention, devices are generally assigned at a non-zero
        multiple of 0x00001000, but other addresses are valid and
        permitted by libvirt.  Each address has the following
        additional attribute: <code>reg</code> (the hex value address
        of the starting register).  <span class="since">Since
        0.9.9.</span>
      </dd>
      <dt><code>ccw</code></dt>
      <dd>S390 guests with a <code>machine</code> value of
        s390-ccw-virtio use the native CCW bus for I/O devices.
        CCW bus addresses have the following additional attributes:
        <code>cssid</code> (a hex value between 0 and 0xfe, inclusive),
        <code>ssid</code> (a value between 0 and 3, inclusive) and
        <code>devno</code> (a hex value between 0 and 0xffff, inclusive).
        Partially specified bus addresses are not allowed.
        If omitted, libvirt will assign a free bus address with
        cssid=0xfe and ssid=0. Virtio-ccw devices must have their cssid
        set to 0xfe.
        <span class="since">Since 1.0.4</span>
      </dd>
      <dt><code>virtio-mmio</code></dt>
      <dd>This places the device on the virtio-mmio transport, which is
        currently only available for some <code>armv7l</code> and
        <code>aarch64</code> virtual machines. virtio-mmio addresses
        do not have any additional attributes.
        <span class="since">Since 1.1.3</span><br/>
        If the guest architecture is <code>aarch64</code> and the machine
        type is <code>virt</code>, libvirt will automatically assign PCI
        addresses to devices; however, the presence of a single device
        with virtio-mmio address in the guest configuration will cause
        libvirt to assign virtio-mmio addresses to all further devices.
        <span class="since">Since 3.0.0</span>
      </dd>
      <dt><code>isa</code></dt>
      <dd>ISA addresses have the following additional
        attributes: <code>iobase</code> and <code>irq</code>.
        <span class="since">Since 1.2.1</span>
      </dd>
    </dl>

    <h4><a id="elementsVirtio">Virtio-related options</a></h4>

    <p>
      QEMU's virtio devices have some attributes related to the virtio transport under
      the <code>driver</code> element:
      The <code>iommu</code> attribute enables the use of emulated IOMMU
      by the device. The attribute <code>ats</code> controls the Address
      Translation Service support for PCIe devices. This is needed to make use
      of IOTLB support (see <a href="#elementsIommu">IOMMU device</a>).
      Possible values are <code>on</code> or <code>off</code>.
      <span class="since">Since 3.5.0</span>
    </p>

    <h4><a id="elementsVirtioTransitional">Virtio transitional devices</a></h4>

    <p>
      <span class="since">Since 5.2.0</span>, some of QEMU's virtio devices,
      when used with PCI/PCIe machine types, accept the following
      <code>model</code> values:
    </p>

    <dl>
      <dt><code>virtio-transitional</code></dt>
      <dd>This device can work both with virtio 0.9 and virtio 1.0 guest
      drivers, so it's the best choice when compatibility with older
      guest operating systems is desired. libvirt will plug the device
      into a conventional PCI slot.
      </dd>
      <dt><code>virtio-non-transitional</code></dt>
      <dd>This device can only work with virtio 1.0 guest drivers, and it's
      the recommended option unless compatibility with older guest
      operating systems is necessary. libvirt will plug the device into
      either a PCI Express slot or a conventional PCI slot based on the
      machine type, resulting in a more optimized PCI topology.
      </dd>
      <dt><code>virtio</code></dt>
      <dd>This device will work like a <code>virtio-non-transitional</code>
      device when plugged into a PCI Express slot, and like a
      <code>virtio-transitional</code> device otherwise; libvirt will
      pick one or the other based on the machine type. This is the best
      choice when compatibility with libvirt versions older than 5.2.0
      is necessary, but it's otherwise not recommended to use it.
      </dd>
    </dl>

    <p>
      While the information outlined above applies to most virtio devices,
      there are a few exceptions:
    </p>

    <ul>
      <li>
        for SCSI controllers, <code>virtio-scsi</code> must be used instead
        of <code>virtio</code> for backwards compatibility reasons;
      </li>
      <li>
        some devices, such as GPUs and input devices (keyboard, tablet and
        mouse), are only defined in the virtio 1.0 spec and as such don't
        have a transitional variant: the only accepted model is
        <code>virtio</code>, which will result in a non-transitional device.
      </li>
    </ul>

    <p>
      For more details see the
      <a href="https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg00923.html">qemu patch posting</a> and the
      <a href="http://docs.oasis-open.org/virtio/virtio/v1.0/virtio-v1.0.html">virtio-1.0 spec</a>.
    </p>


    <h4><a id="elementsControllers">Controllers</a></h4>

    <p>
      Depending on the guest architecture, some device buses can
      appear more than once, with a group of virtual devices tied to a
      virtual controller.  Normally, libvirt can automatically infer such
      controllers without requiring explicit XML markup, but sometimes
      it is necessary to provide an explicit controller element, notably
      when planning the <a href="pci-hotplug.html">PCI topology</a>
      for guests where device hotplug is expected.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;controller type='ide' index='0'/&gt;
  &lt;controller type='virtio-serial' index='0' ports='16' vectors='4'/&gt;
  &lt;controller type='virtio-serial' index='1'&gt;
    &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/&gt;
  &lt;/controller&gt;
  &lt;controller type='scsi' index='0' model='virtio-scsi'&gt;
    &lt;driver iothread='4'/&gt;
    &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x0b' function='0x0'/&gt;
  &lt;/controller&gt;
  &lt;controller type='xenbus' maxGrantFrames='64'/&gt;
  ...
&lt;/devices&gt;
...</pre>

    <p>
      Each controller has a mandatory attribute <code>type</code>,
      which must be one of 'ide', 'fdc', 'scsi', 'sata', 'usb',
      'ccid', 'virtio-serial' or 'pci', and a mandatory
      attribute <code>index</code> which is the decimal integer
      describing in which order the bus controller is encountered (for
      use in <code>controller</code> attributes of
      <code>&lt;address&gt;</code> elements).
      <span class="since">Since 1.3.5</span> the index is optional; if
      not specified, it will be auto-assigned to be the lowest unused
      index for the given controller type. Some controller types have
      additional attributes that control specific features, such as:
    </p>

      <dl>
        <dt><code>virtio-serial</code></dt>
        <dd>The <code>virtio-serial</code> controller has two additional
        optional attributes <code>ports</code> and <code>vectors</code>,
        which control how many devices can be connected through the
        controller. <span class="since">Since 5.2.0</span>, it
        supports an optional attribute <code>model</code> which can
        be 'virtio', 'virtio-transitional', or 'virtio-non-transitional'. See
        <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
        for more details.
        </dd>
        <dt><code>scsi</code></dt>
        <dd>A <code>scsi</code> controller has an optional attribute
        <code>model</code>, which is one of 'auto', 'buslogic', 'ibmvscsi',
        'lsilogic', 'lsisas1068', 'lsisas1078', 'virtio-scsi',
        'vmpvscsi', 'virtio-transitional', 'virtio-non-transitional'. See
        <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
        for more details.
        </dd>
        <dt><code>usb</code></dt>
        <dd>A <code>usb</code> controller has an optional attribute
        <code>model</code>, which is one of "piix3-uhci", "piix4-uhci",
        "ehci", "ich9-ehci1", "ich9-uhci1", "ich9-uhci2", "ich9-uhci3",
        "vt82c686b-uhci", "pci-ohci", "nec-xhci", "qusb1" (xen pvusb
        with qemu backend, version 1.1), "qusb2" (xen pvusb with qemu
        backend, version 2.0) or "qemu-xhci". Additionally,
         <span class="since">since 0.10.0</span>, if the USB bus needs to
         be explicitly disabled for the guest, <code>model='none'</code>
         may be used.  <span class="since">Since 1.0.5</span>, no default
         USB controller will be built on s390.
         <span class="since">Since 1.3.5</span>, USB controllers accept a
         <code>ports</code> attribute to configure how many devices can be
         connected to the controller.</dd>
        <dt><code>ide</code></dt>
        <dd><span class="since">Since 3.10.0</span> for the vbox driver, the
        <code>ide</code> controller has an optional attribute
        <code>model</code>, which is one of "piix3", "piix4" or "ich6".</dd>
        <dt><code>xenbus</code></dt>
        <dd><span class="since">Since 5.2.0</span>, the <code>xenbus</code>
        controller has an optional attribute <code>maxGrantFrames</code>,
        which specifies the maximum number of grant frames the controller
        makes available for connected devices.</dd>
      </dl>

    <p>
      Note: The PowerPC64 "spapr-vio" addresses do not have an
      associated controller.
    </p>

    <p>
      For controllers that are themselves devices on a PCI or USB bus,
      an optional sub-element <code>&lt;address&gt;</code> can specify
      the exact relationship of the controller to its master bus, with
      semantics <a href="#elementsAddress">given above</a>.
    </p>

    <p>
      An optional sub-element <code>driver</code> can specify the driver
      specific options:
    </p>
    <dl>
      <dt><code>queues</code></dt>
      <dd>
        The optional <code>queues</code> attribute specifies the number of
        queues for the controller. For best performance, it's recommended to
        specify a value matching the number of vCPUs.
        <span class="since">Since 1.0.5 (QEMU and KVM only)</span>
      </dd>
      <dt><code>cmd_per_lun</code></dt>
      <dd>
        The optional <code>cmd_per_lun</code> attribute specifies the maximum
        number of commands that can be queued on devices controlled by the
        host.
        <span class="since">Since 1.2.7 (QEMU and KVM only)</span>
      </dd>
      <dt><code>max_sectors</code></dt>
      <dd>
        The optional <code>max_sectors</code> attribute specifies the maximum
        amount of data in bytes that will be transferred to or from the device
        in a single command. The transfer length is measured in sectors, where
        a sector is 512 bytes.
        <span class="since">Since 1.2.7 (QEMU and KVM only)</span>
      </dd>
      <dt><code>ioeventfd</code></dt>
      <dd>
        The optional <code>ioeventfd</code> attribute specifies
        whether the controller should use
        <a href='https://patchwork.kernel.org/patch/43390/'>
        I/O asynchronous handling</a> or not.  Accepted values are
        "on" and "off". <span class="since">Since 1.2.18</span>
      </dd>
      <dt><code>iothread</code></dt>
      <dd>
        Supported for controller type <code>scsi</code> using model
        <code>virtio-scsi</code> for <code>address</code> types
        <code>pci</code> and <code>ccw</code>
        <span class="since">since 1.3.5 (QEMU 2.4)</span>.

        The optional <code>iothread</code> attribute assigns the controller
        to an IOThread as defined by the range for the domain
        <a href="#elementsIOThreadsAllocation"><code>iothreads</code></a>
        value. Each SCSI <code>disk</code> assigned to use the specified
        <code>controller</code> will utilize the same IOThread. If a specific
        IOThread is desired for a specific SCSI <code>disk</code>, then
        multiple controllers must be defined each having a specific
        <code>iothread</code> value. The <code>iothread</code> value
        must be within the range 1 to the domain iothreads value.
      </dd>
      <dt>virtio options</dt>
      <dd>
        For virtio controllers,
        <a href="#elementsVirtio">Virtio-specific options</a> can also be
        set. (<span class="since">Since 3.5.0</span>)
      </dd>
    </dl>
    <p>
      USB companion controllers have an optional
      sub-element <code>&lt;master&gt;</code> to specify the exact
      relationship of the companion to its master controller.
      A companion controller is on the same bus as its master, so
      the companion <code>index</code> value should be equal.
      Not all controller models can be used as companion controllers
      and libvirt might provide some sensible defaults (settings
      of <code>master startport</code> and <code>function</code> of an
      address) for some particular models.
      Preferred companion controllers are <code>ich-uhci[123]</code>.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;controller type='usb' index='0' model='ich9-ehci1'&gt;
    &lt;address type='pci' domain='0' bus='0' slot='4' function='7'/&gt;
  &lt;/controller&gt;
  &lt;controller type='usb' index='0' model='ich9-uhci1'&gt;
    &lt;master startport='0'/&gt;
    &lt;address type='pci' domain='0' bus='0' slot='4' function='0' multifunction='on'/&gt;
  &lt;/controller&gt;
  ...
&lt;/devices&gt;
...</pre>

    <p>
      PCI controllers have an optional <code>model</code> attribute; possible
      values for this attribute are
    </p>
    <ul>
      <li>
        <code>pci-root</code>, <code>pci-bridge</code>
        (<span class="since">since 1.0.5</span>)
      </li>
      <li>
        <code>pcie-root</code>, <code>dmi-to-pci-bridge</code>
        (<span class="since">since 1.1.2</span>)
      </li>
      <li>
        <code>pcie-root-port</code>, <code>pcie-switch-upstream-port</code>,
        <code>pcie-switch-downstream-port</code>
        (<span class="since">since 1.2.19</span>)
      </li>
      <li>
        <code>pci-expander-bus</code>, <code>pcie-expander-bus</code>
        (<span class="since">since 1.3.4</span>)
      </li>
      <li>
        <code>pcie-to-pci-bridge</code>
        (<span class="since">since 4.3.0</span>)
      </li>
    </ul>
    <p>
      The root controllers (<code>pci-root</code>
      and <code>pcie-root</code>) have an
      optional <code>pcihole64</code> element specifying how big (in
      kilobytes, or in the unit specified by <code>pcihole64</code>'s
      <code>unit</code> attribute) the 64-bit PCI hole should be. Some guests (like
      Windows XP or Windows Server 2003) might crash when QEMU and Seabios
      are recent enough to support 64-bit PCI holes, unless this is disabled
      (set to 0). <span class="since">Since 1.1.2 (QEMU only)</span>
    </p>
    <p>
      PCI controllers also have an optional
      subelement <code>&lt;model&gt;</code> with an attribute
      <code>name</code>. The name attribute holds the name of the
      specific device that qemu is emulating (e.g. "i82801b11-bridge")
      rather than simply the class of device ("pcie-to-pci-bridge",
      "pci-bridge"), which is set in the controller element's
      model <b>attribute</b>.  In almost all cases, you should not
      manually add a <code>&lt;model&gt;</code> subelement to a
      controller, nor should you modify one that is automatically
      generated by libvirt. <span class="since">Since 1.2.19 (QEMU
      only).</span>
    </p>
    <p>
      PCI controllers also have an optional
      subelement <code>&lt;target&gt;</code> with the attributes and
      subelements listed below. These are configurable items that 1)
      are visible to the guest OS so must be preserved for guest ABI
      compatibility, and 2) are usually left to default values or
      derived automatically by libvirt. In almost all cases, you
      should not manually add a <code>&lt;target&gt;</code> subelement
      to a controller, nor should you modify the values in the those
      that are automatically generated by
      libvirt. <span class="since">Since 1.2.19 (QEMU only).</span>
    </p>
    <dl>
      <dt><code>chassisNr</code></dt>
      <dd>
        PCI controllers that have attribute model="pci-bridge", can
        also have a <code>chassisNr</code> attribute in
        the <code>&lt;target&gt;</code> subelement, which is used to
        control QEMU's "chassis_nr" option for the pci-bridge device
        (normally libvirt automatically sets this to the same value as
        the index attribute of the pci controller). If set, chassisNr
        must be between 1 and 255.
      </dd>
      <dt><code>chassis</code></dt>
      <dd>
        pcie-root-port and pcie-switch-downstream-port controllers can
        also have a <code>chassis</code> attribute in
        the <code>&lt;target&gt;</code> subelement, which is used to
        set the controller's "chassis" configuration value, which is
        visible to the virtual machine. If set, chassis must be
        between 0 and 255.
      </dd>
      <dt><code>port</code></dt>
      <dd>
        pcie-root-port and pcie-switch-downstream-port controllers can
        also have a <code>port</code> attribute in
        the <code>&lt;target&gt;</code> subelement, which
        is used to set the controller's "port" configuration value,
        which is visible to the virtual machine. If set, port must be
        between 0 and 255.
      </dd>
      <dt><code>busNr</code></dt>
      <dd>
        pci-expander-bus and pcie-expander-bus controllers can have an
        optional <code>busNr</code> attribute (1-254). This will be
        the bus number of the new bus; All bus numbers between that
        specified and 255 will be available only for assignment to
        PCI/PCIe controllers plugged into the hierarchy starting with
        this expander bus, and bus numbers less than the specified
        value will be available to the next lower expander-bus (or the
        root-bus if there are no lower expander buses). If you do not
        specify a busNumber, libvirt will find the lowest existing
        busNumber in all other expander buses (or use 256 if there are
        no others) and auto-assign the busNr of that found bus - 2,
        which provides one bus number for the pci-expander-bus and one
        for the pci-bridge that is automatically attached to it (if
        you plan on adding more pci-bridges to the hierarchy of the
        bus, you should manually set busNr to a lower value).
        <p>
          A similar algorithm is used for automatically determining
          the busNr attribute for pcie-expander-bus, but since the
          pcie-expander-bus doesn't have any built-in pci-bridge, the
          2nd bus-number is just being reserved for the pcie-root-port
          that must necessarily be connected to the bus in order to
          actually plug in an endpoint device. If you intend to plug
          multiple devices into a pcie-expander-bus, you must connect
          a pcie-switch-upstream-port to the pcie-root-port that is
          plugged into the pcie-expander-bus, and multiple
          pcie-switch-downstream-ports to the
          pcie-switch-upstream-port, and of course for this to work
          properly, you will need to decrease the pcie-expander-bus'
          busNr accordingly so that there are enough unused bus
          numbers above it to accommodate giving out one bus number for
          the upstream-port and one for each downstream-port (in
          addition to the pcie-root-port and the pcie-expander-bus
          itself).
        </p>
      </dd>
      <dt><code>node</code></dt>
      <dd>
        Some PCI controllers (<code>pci-expander-bus</code> for the pc
        machine type, <code>pcie-expander-bus</code> for the q35 machine
        type and, <span class="since">since 3.6.0</span>,
        <code>pci-root</code> for the pseries machine type) can have an
        optional <code>&lt;node&gt;</code> subelement within
        the <code>&lt;target&gt;</code> subelement, which is used to
        set the NUMA node reported to the guest OS for that bus - the
        guest OS will then know that all devices on that bus are a
        part of the specified NUMA node (it is up to the user of the
        libvirt API to attach host devices to the correct
        pci-expander-bus when assigning them to the domain).
      </dd>
      <dt><code>index</code></dt>
      <dd>
        pci-root controllers for pSeries guests use this attribute to
        record the order they will show up in the guest.
        <span class="since">Since 3.6.0</span>
      </dd>
    </dl>
    <p>
      For machine types which provide an implicit PCI bus, the pci-root
      controller with index=0 is auto-added and required to use PCI devices.
      pci-root has no address.
      PCI bridges are auto-added if there are too many devices to fit on
      the one bus provided by pci-root, or a PCI bus number greater than zero
      was specified.
      PCI bridges can also be specified manually, but their addresses should
      only refer to PCI buses provided by already specified PCI controllers.
      Leaving gaps in the PCI controller indexes might lead to an invalid
      configuration.
    </p>
<pre>
...
&lt;devices&gt;
  &lt;controller type='pci' index='0' model='pci-root'/&gt;
  &lt;controller type='pci' index='1' model='pci-bridge'&gt;
    &lt;address type='pci' domain='0' bus='0' slot='5' function='0' multifunction='off'/&gt;
  &lt;/controller&gt;
&lt;/devices&gt;
...</pre>

    <p>
      For machine types which provide an implicit PCI Express (PCIe)
      bus (for example, the machine types based on the Q35 chipset),
      the pcie-root controller with index=0 is auto-added to the
      domain's configuration. pcie-root has also no address, provides
      31 slots (numbered 1-31) that can be used to attach PCIe or PCI
      devices (although libvirt will never auto-assign a PCI device to
      a PCIe slot, it will allow manual specification of such an
      assignment). Devices connected to pcie-root cannot be
      hotplugged. If traditional PCI devices are present in the guest
      configuration, a <code>pcie-to-pci-bridge</code> controller will
      automatically be added: this controller, which plugs into a
      <code>pcie-root-port</code>, provides 31 usable PCI slots (1-31) with
      hotplug support (<span class="since">since 4.3.0</span>). If the QEMU
      binary doesn't support the corresponding device, then a
      <code>dmi-to-pci-bridge</code> controller will be added instead,
      usually at the defacto standard location of slot=0x1e. A
      dmi-to-pci-bridge controller plugs into a PCIe slot (as provided
      by pcie-root), and itself provides 31 standard PCI slots (which
      also do not support device hotplug). In order to have
      hot-pluggable PCI slots in the guest system, a pci-bridge
      controller will also be automatically created and connected to
      one of the slots of the auto-created dmi-to-pci-bridge
      controller; all guest PCI devices with addresses that are
      auto-determined by libvirt will be placed on this pci-bridge
      device.  (<span class="since">since 1.1.2</span>).
    </p>
    <p>
      Domains with an implicit pcie-root can also add controllers
      with <code>model='pcie-root-port'</code>,
      <code>model='pcie-switch-upstream-port'</code>,
      and <code>model='pcie-switch-downstream-port'</code>. pcie-root-port
      is a simple type of bridge device that can connect only to one
      of the 31 slots on the pcie-root bus on its upstream side, and
      makes a single (PCIe, hotpluggable) port available on the
      downstream side (at slot='0'). pcie-root-port can be used to
      provide a single slot to later hotplug a PCIe device (but is not
      itself hotpluggable - it must be in the configuration when the
      domain is started).
      (<span class="since">since 1.2.19</span>)
    </p>
    <p>
      pcie-switch-upstream-port is a more flexible (but also more
      complex) device that can only plug into a pcie-root-port or
      pcie-switch-downstream-port on the upstream side (and only
      before the domain is started - it is not hot-pluggable), and
      provides 32 ports on the downstream side (slot='0' - slot='31')
      that accept only pcie-switch-downstream-port devices; each
      pcie-switch-downstream-port device can only plug into a
      pcie-switch-upstream-port on its upstream side (again, not
      hot-pluggable), and on its downstream side provides a single
      hotpluggable pcie port that can accept any standard pci or pcie
      device (or another pcie-switch-upstream-port), i.e. identical in
      function to a pcie-root-port.  (<span class="since">since
      1.2.19</span>)
    </p>
<pre>
...
&lt;devices&gt;
  &lt;controller type='pci' index='0' model='pcie-root'/&gt;
  &lt;controller type='pci' index='1' model='pcie-root-port'&gt;
    &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/&gt;
  &lt;/controller&gt;
  &lt;controller type='pci' index='2' model='pcie-to-pci-bridge'&gt;
    &lt;address type='pci' domain='0x0000' bus='0x01' slot='0x00' function='0x0'/&gt;
  &lt;/controller&gt;
&lt;/devices&gt;
...</pre>

    <h4><a id="elementsLease">Device leases</a></h4>

    <p>
      When using a lock manager, it may be desirable to record device leases
      against a VM. The lock manager will ensure the VM won't start unless
      the leases can be acquired.
    </p>

<pre>
...
&lt;devices&gt;
  ...
  &lt;lease&gt;
    &lt;lockspace&gt;somearea&lt;/lockspace&gt;
    &lt;key&gt;somekey&lt;/key&gt;
    &lt;target path='/some/lease/path' offset='1024'/&gt;
  &lt;/lease&gt;
  ...
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>lockspace</code></dt>
      <dd>This is an arbitrary string, identifying the lockspace
        within which the key is held. Lock managers may impose
        extra restrictions on the format, or length of the lockspace
        name.</dd>
      <dt><code>key</code></dt>
      <dd>This is an arbitrary string, uniquely identifying the
        lease to be acquired. Lock managers may impose extra
        restrictions on the format, or length of the key.
      </dd>
      <dt><code>target</code></dt>
      <dd>This is the fully qualified path of the file associated
        with the lockspace. The offset specifies where the lease
        is stored within the file. If the lock manager does not
        require an offset, just pass 0.
      </dd>
    </dl>

    <h4><a id="elementsHostDev">Host device assignment</a></h4>

    <h5><a id="elementsHostDevSubsys">USB / PCI / SCSI devices</a></h5>

    <p>
      USB, PCI and SCSI devices attached to the host can be passed through
      to the guest using the <code>hostdev</code> element.
      <span class="since">since after 0.4.4 for USB, 0.6.0 for PCI (KVM only)
        and 1.0.6 for SCSI (KVM only)</span>:
    </p>

<pre>
...
&lt;devices&gt;
  &lt;hostdev mode='subsystem' type='usb'&gt;
    &lt;source startupPolicy='optional'&gt;
      &lt;vendor id='0x1234'/&gt;
      &lt;product id='0xbeef'/&gt;
    &lt;/source&gt;
    &lt;boot order='2'/&gt;
  &lt;/hostdev&gt;
&lt;/devices&gt;
...</pre>

    <p>or:</p>

<pre>
...
&lt;devices&gt;
  &lt;hostdev mode='subsystem' type='pci' managed='yes'&gt;
    &lt;source&gt;
      &lt;address domain='0x0000' bus='0x06' slot='0x02' function='0x0'/&gt;
    &lt;/source&gt;
    &lt;boot order='1'/&gt;
    &lt;rom bar='on' file='/etc/fake/boot.bin'/&gt;
  &lt;/hostdev&gt;
&lt;/devices&gt;
...</pre>

    <p>or:</p>

<pre>
...
&lt;devices&gt;
  &lt;hostdev mode='subsystem' type='scsi' sgio='filtered' rawio='yes'&gt;
    &lt;source&gt;
      &lt;adapter name='scsi_host0'/&gt;
      &lt;address bus='0' target='0' unit='0'/&gt;
    &lt;/source&gt;
    &lt;readonly/&gt;
    &lt;address type='drive' controller='0' bus='0' target='0' unit='0'/&gt;
  &lt;/hostdev&gt;
&lt;/devices&gt;
...</pre>


    <p>or:</p>

<pre>
...
&lt;devices&gt;
  &lt;hostdev mode='subsystem' type='scsi'&gt;
    &lt;source protocol='iscsi' name='iqn.2014-08.com.example:iscsi-nopool/1'&gt;
      &lt;host name='example.com' port='3260'/&gt;
      &lt;auth username='myuser'&gt;
        &lt;secret type='iscsi' usage='libvirtiscsi'/&gt;
      &lt;/auth&gt;
    &lt;/source&gt;
    &lt;address type='drive' controller='0' bus='0' target='0' unit='0'/&gt;
  &lt;/hostdev&gt;
&lt;/devices&gt;
...</pre>

    <p>or:</p>

<pre>
  ...
  &lt;devices&gt;
    &lt;hostdev mode='subsystem' type='scsi_host'&gt;
      &lt;source protocol='vhost' wwpn='naa.50014057667280d8'/&gt;
    &lt;/hostdev&gt;
  &lt;/devices&gt;
  ...</pre>

    <p>or:</p>

<pre>
  ...
  &lt;devices&gt;
    &lt;hostdev mode='subsystem' type='mdev' model='vfio-pci'&gt;
    &lt;source&gt;
      &lt;address uuid='c2177883-f1bb-47f0-914d-32a22e3a8804'/&gt;
    &lt;/source&gt;
    &lt;/hostdev&gt;
    &lt;hostdev mode='subsystem' type='mdev' model='vfio-ccw'&gt;
    &lt;source&gt;
      &lt;address uuid='9063cba3-ecef-47b6-abcf-3fef4fdcad85'/&gt;
    &lt;/source&gt;
    &lt;address type='ccw' cssid='0xfe' ssid='0x0' devno='0x0001'/&gt;
    &lt;/hostdev&gt;
  &lt;/devices&gt;
  ...</pre>

    <dl>
      <dt><code>hostdev</code></dt>
      <dd>The <code>hostdev</code> element is the main container for describing
        host devices. For each device, the <code>mode</code> is always
        "subsystem" and the <code>type</code> is one of the following values
        with additional attributes noted.
        <dl>
          <dt><code>usb</code></dt>
          <dd>USB devices are detached from the host on guest startup
            and reattached after the guest exits or the device is
            hot-unplugged.
          </dd>
          <dt><code>pci</code></dt>
          <dd>For PCI devices, when <code>managed</code> is "yes" it is
            detached from the host before being passed on to the guest
            and reattached to the host after the guest exits. If
            <code>managed</code> is omitted or "no", the user is
            responsible to call <code>virNodeDeviceDetachFlags</code>
            (or <code>virsh nodedev-detach</code> before starting the guest
            or hot-plugging the device and <code>virNodeDeviceReAttach</code>
            (or <code>virsh nodedev-reattach</code>) after hot-unplug or
            stopping the guest.
          </dd>
          <dt><code>scsi</code></dt>
          <dd>For SCSI devices, user is responsible to make sure the device
            is not used by host. If supported by the hypervisor and OS, the
            optional <code>sgio</code> (<span class="since">since 1.0.6</span>)
            attribute indicates whether unprivileged SG_IO commands are
            filtered for the disk. Valid settings are "filtered" or
            "unfiltered", where the default is "filtered".
            The optional <code>rawio</code>
            (<span class="since">since 1.2.9</span>) attribute indicates
            whether the lun needs the rawio capability. Valid settings are
            "yes" or "no". See the rawio description within the
            <a href="#elementsDisks">disk</a> section.
            If a disk lun in the domain already has the rawio capability,
            then this setting not required.
          </dd>
          <dt><code>scsi_host</code></dt>
          <dd><span class="since">since 2.5.0</span>For SCSI devices, user
            is responsible to make sure the device is not used by host. This
            <code>type</code> passes all LUNs presented by a single HBA to
            the guest. <span class="since">Since 5.2.0,</span> the
            <code>model</code> attribute can be specified further
            with "virtio-transitional", "virtio-non-transitional", or
            "virtio". See
            <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
            for more details.
          </dd>
          <dt><code>mdev</code></dt>
          <dd>For mediated devices (<span class="since">Since 3.2.0</span>)
          the <code>model</code> attribute specifies the device API which
          determines how the host's vfio driver will expose the device to the
          guest. Currently, <code>model='vfio-pci'</code>,
          <code>model='vfio-ccw'</code> (<span class="since">Since 4.4.0</span>)
          and <code>model='vfio-ap'</code> (<span class="since">Since 4.9.0</span>)
          is supported. <a href="drvnodedev.html#MDEV">MDEV</a> section
          provides more information about mediated devices as well as how to
          create mediated devices on the host.
          <span class="since">Since 4.6.0 (QEMU 2.12)</span> an optional
          <code>display</code> attribute may be used to enable or disable
          support for an accelerated remote desktop backed by a mediated
          device (such as NVIDIA vGPU or Intel GVT-g) as an alternative to
          emulated <a href="#elementsVideo">video devices</a>. This attribute
          is limited to <code>model='vfio-pci'</code> only. Supported values
          are either <code>on</code> or <code>off</code> (default is 'off').
          It is required to use a
          <a href="#elementsGraphics">graphical framebuffer</a> in order to
          use this attribute, currently only supported with VNC, Spice and
          egl-headless graphics devices.
          <p>
            Note: There are also some implications on the usage of guest's
            address type depending on the <code>model</code> attribute,
            see the <code>address</code> element below.
          </p>
          </dd>
        </dl>
        <p>
          Note: The <code>managed</code> attribute is only used with
          <code>type='pci'</code> and is ignored by all the other device types,
          thus setting <code>managed</code> explicitly with other than a PCI
          device has the same effect as omitting it. Similarly,
          <code>model</code> attribute is only supported by mediated devices and
          ignored by all other device types.
        </p>
      </dd>
      <dt><code>source</code></dt>
      <dd>The source element describes the device as seen from the host using
        the following mechanism to describe:
        <dl>
          <dt><code>usb</code></dt>
          <dd>The USB device can either be addressed by vendor / product id
            using the <code>vendor</code> and <code>product</code> elements
            or by the device's address on the host using the
            <code>address</code> element.
            <p>
            <span class="since">Since 1.0.0</span>, the <code>source</code>
            element of USB devices may contain <code>startupPolicy</code>
            attribute which can be used to define policy what to do if the
            specified host USB device is not found. The attribute accepts
            the following values:
            </p>
            <table class="top_table">
              <tr>
                <td> mandatory </td>
                <td> fail if missing for any reason (the default) </td>
              </tr>
              <tr>
                <td> requisite </td>
                <td> fail if missing on boot up,
                     drop if missing on migrate/restore/revert </td>
              </tr>
              <tr>
                <td> optional </td>
                <td> drop if missing at any start attempt </td>
              </tr>
            </table>
          </dd>
          <dt><code>pci</code></dt>
          <dd>PCI devices can only be described by their <code>address</code>.
          </dd>
          <dt><code>scsi</code></dt>
          <dd>SCSI devices are described by both the <code>adapter</code>
            and <code>address</code> elements. The <code>address</code>
            element includes a <code>bus</code> attribute (a 2-digit bus
            number), a <code>target</code> attribute (a 10-digit target
            number), and a <code>unit</code> attribute (a 20-digit unit
            number on the bus). Not all hypervisors support larger
            <code>target</code> and <code>unit</code> values. It is up
            to each hypervisor to determine the maximum value supported
            for the adapter.
            <p>
            <span class="since">Since 1.2.8</span>, the <code>source</code>
            element of a SCSI device may contain the <code>protocol</code>
            attribute. When the attribute is set to "iscsi", the host
            device XML follows the network <a href="#elementsDisks">disk</a>
            device using the same <code>name</code> attribute and optionally
            using the <code>auth</code> element to provide the authentication
            credentials to the iSCSI server.
            </p>
          </dd>
          <dt><code>scsi_host</code></dt>
          <dd><span class="since">Since 2.5.0</span>, multiple LUNs behind a
            single SCSI HBA are described by a <code>protocol</code>
            attribute set to "vhost" and a <code>wwpn</code> attribute that
            is the vhost_scsi wwpn (16 hexadecimal digits with a prefix of
            "naa.") established in the host configfs.
          </dd>
          <dt><code>mdev</code></dt>
          <dd>Mediated devices (<span class="since">Since 3.2.0</span>) are
            described by the <code>address</code> element. The
            <code>address</code> element contains a single mandatory attribute
            <code>uuid</code>.
          </dd>
        </dl>
      </dd>
      <dt><code>vendor</code>, <code>product</code></dt>
      <dd>The <code>vendor</code> and <code>product</code> elements each have an
      <code>id</code> attribute that specifies the USB vendor and product id.
      The ids can be given in decimal, hexadecimal (starting with 0x) or
      octal (starting with 0) form.</dd>
      <dt><code>boot</code></dt>
      <dd>Specifies that the device is bootable. The <code>order</code>
      attribute determines the order in which devices will be tried during
      boot sequence. The per-device <code>boot</code> elements cannot be
      used together with general boot elements in
      <a href="#elementsOSBIOS">BIOS bootloader</a> section.
      <span class="since">Since 0.8.8</span> for PCI devices,
      <span class="since">Since 1.0.1</span> for USB devices.
      </dd>
      <dt><code>rom</code></dt>
      <dd>The <code>rom</code> element is used to change how a PCI
        device's ROM is presented to the guest. The optional <code>bar</code>
        attribute can be set to "on" or "off", and determines whether
        or not the device's ROM will be visible in the guest's memory
        map. (In PCI documentation, the "rombar" setting controls the
        presence of the Base Address Register for the ROM). If no rom
        bar is specified, the qemu default will be used (older
        versions of qemu used a default of "off", while newer qemus
        have a default of "on"). <span class="since">Since
        0.9.7 (QEMU and KVM only)</span>. The optional
        <code>file</code> attribute contains an absolute path to a binary file
        to be presented to the guest as the device's ROM BIOS. This
        can be useful, for example, to provide a PXE boot ROM for a
        virtual function of an sr-iov capable ethernet device (which
        has no boot ROMs for the VFs).
        <span class="since">Since 0.9.10 (QEMU and KVM only)</span>.
        The optional <code>enabled</code> attribute can be set to
        <code>no</code> to disable PCI ROM loading completely for the device;
        if PCI ROM loading is disabled through this attribute, attempts to
        tweak the loading process further using the <code>bar</code> or
        <code>file</code> attributes will be rejected.
        <span class="since">Since 4.3.0 (QEMU and KVM only)</span>.
      </dd>
      <dt><code>address</code></dt>
      <dd>The <code>address</code> element for USB devices has a
      <code>bus</code> and <code>device</code> attribute to specify the
      USB bus and device number the device appears at on the host.
      The values of these attributes can be given in decimal, hexadecimal
      (starting with 0x) or octal (starting with 0) form.
      For PCI devices the element carries 4 attributes allowing to designate
      the device as can be found with the <code>lspci</code> or
      with <code>virsh nodedev-list</code>. For SCSI devices a 'drive'
      address type must be used. For mediated devices, which are software-only
      devices defining an allocation of resources on the physical parent device,
      the address type used must conform to the <code>model</code> attribute
      of element <code>hostdev</code>, e.g. any address type other than PCI for
      <code>vfio-pci</code> device API or any address type other than CCW for
      <code>vfio-ccw</code> device API will result in an error.
      <a href="#elementsAddress">See above</a> for more details on the address
      element.</dd>
      <dt><code>driver</code></dt>
      <dd>
        PCI devices can have an optional <code>driver</code>
        subelement that specifies which backend driver to use for PCI
        device assignment. Use the <code>name</code> attribute to
        select either "vfio" (for the new VFIO device assignment
        backend, which is compatible with UEFI SecureBoot) or "kvm"
        (the legacy device assignment handled directly by the KVM
        kernel module)<span class="since">Since 1.0.5 (QEMU and KVM
        only, requires kernel 3.6 or newer)</span>. When specified,
        device assignment will fail if the requested method of device
        assignment isn't available on the host. When not specified,
        the default is "vfio" on systems where the VFIO driver is
        available and loaded, and "kvm" on older systems, or those
        where the VFIO driver hasn't been
        loaded <span class="since">Since 1.1.3</span> (prior to that
        the default was always "kvm").
      </dd>
      <dt><code>readonly</code></dt>
      <dd>Indicates that the device is readonly, only supported by SCSI host
        device now. <span class="since">Since 1.0.6 (QEMU and KVM only)</span>
      </dd>
      <dt><code>shareable</code></dt>
      <dd>If present, this indicates the device is expected to be shared
        between domains (assuming the hypervisor and OS support this).
        Only supported by SCSI host device.
        <span class="since">Since 1.0.6</span>
        <p>
          Note: Although <code>shareable</code> was introduced
          <span class="since">in 1.0.6</span>, it did not work as
          as expected until <span class="since">1.2.2</span>.
        </p>
      </dd>
    </dl>


    <h5><a id="elementsHostDevCaps">Block / character devices</a></h5>

    <p>
      Block / character devices from the host can be passed through
      to the guest using the <code>hostdev</code> element. This is
      only possible with container based virtualization. Devices are specified
      by a fully qualified path.
      <span class="since">since after 1.0.1 for LXC</span>:
    </p>

    <pre>
...
&lt;hostdev mode='capabilities' type='storage'&gt;
  &lt;source&gt;
    &lt;block&gt;/dev/sdf1&lt;/block&gt;
  &lt;/source&gt;
&lt;/hostdev&gt;
...
    </pre>

    <pre>
...
&lt;hostdev mode='capabilities' type='misc'&gt;
  &lt;source&gt;
    &lt;char&gt;/dev/input/event3&lt;/char&gt;
  &lt;/source&gt;
&lt;/hostdev&gt;
...
    </pre>

    <pre>
...
&lt;hostdev mode='capabilities' type='net'&gt;
  &lt;source&gt;
    &lt;interface&gt;eth0&lt;/interface&gt;
  &lt;/source&gt;
&lt;/hostdev&gt;
...
    </pre>

    <dl>
      <dt><code>hostdev</code></dt>
      <dd>The <code>hostdev</code> element is the main container for describing
        host devices. For block/character device passthrough <code>mode</code> is
        always "capabilities" and <code>type</code> is "storage" for a block
        device, "misc" for a character device and "net" for a host network
        interface.
      </dd>
      <dt><code>source</code></dt>
      <dd>The source element describes the device as seen from the host.
        For block devices, the path to the block device in the host
        OS is provided in the nested "block" element, while for character
        devices the "char" element is used. For network interfaces, the
        name of the interface is provided in the "interface" element.
      </dd>
    </dl>

    <h4><a id="elementsRedir">Redirected devices</a></h4>

    <p>
      USB device redirection through a character device is
      supported <span class="since">since after 0.9.5 (KVM
      only)</span>:
    </p>

<pre>
...
&lt;devices&gt;
  &lt;redirdev bus='usb' type='tcp'&gt;
    &lt;source mode='connect' host='localhost' service='4000'/&gt;
    &lt;boot order='1'/&gt;
  &lt;/redirdev&gt;
  &lt;redirfilter&gt;
    &lt;usbdev class='0x08' vendor='0x1234' product='0xbeef' version='2.56' allow='yes'/&gt;
    &lt;usbdev allow='no'/&gt;
  &lt;/redirfilter&gt;
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>redirdev</code></dt>
      <dd>The <code>redirdev</code> element is the main container for
        describing redirected devices. <code>bus</code> must be "usb"
        for a USB device.

        An additional attribute <code>type</code> is required,
        matching one of the
        supported <a href="#elementsConsole">serial device</a> types,
        to describe the host side of the
        tunnel; <code>type='tcp'</code>
        or <code>type='spicevmc'</code> (which uses the usbredir
        channel of a <a href="#elementsGraphics">SPICE graphics
        device</a>) are typical. The redirdev element has an optional
        sub-element <code>&lt;address&gt;</code> which can tie the
        device to a particular controller. Further sub-elements,
        such as <code>&lt;source&gt;</code>, may be required according
        to the given type, although a <code>&lt;target&gt;</code> sub-element
        is not required (since the consumer of the character device is
        the hypervisor itself, rather than a device visible in the guest).
      </dd>
      <dt><code>boot</code></dt>

      <dd>Specifies that the device is bootable.
        The <code>order</code> attribute determines the order in which
        devices will be tried during boot sequence. The per-device
        <code>boot</code> elements cannot be used together with general
        boot elements in  <a href="#elementsOSBIOS">BIOS bootloader</a> section.
        (<span class="since">Since 1.0.1</span>)
      </dd>
      <dt><code>redirfilter</code></dt>
      <dd>The<code> redirfilter </code>element is used for creating the
        filter rule to filter out certain devices from redirection.
        It uses sub-element <code>&lt;usbdev&gt;</code> to define each filter rule.
        <code>class</code> attribute is the USB Class code, for example,
        0x08 represents mass storage devices. The USB device can be addressed by
        vendor / product id using the <code>vendor</code> and <code>product</code> attributes.
        <code>version</code> is the device revision from the bcdDevice field (not
        the version of the USB protocol).
        These four attributes are optional and <code>-1</code> can be used to allow
        any value for them. <code>allow</code> attribute is mandatory,
        'yes' means allow, 'no' for deny.
      </dd>
    </dl>

    <h4><a id="elementsSmartcard">Smartcard devices</a></h4>

    <p>
      A virtual smartcard device can be supplied to the guest via the
      <code>smartcard</code> element. A USB smartcard reader device on
      the host cannot be used on a guest with simple device
      passthrough, since it will then not be available on the host,
      possibly locking the host computer when it is "removed".
      Therefore, some hypervisors provide a specialized virtual device
      that can present a smartcard interface to the guest, with
      several modes for describing how credentials are obtained from
      the host or even a from a channel created to a third-party
      smartcard provider. <span class="since">Since 0.8.8</span>
    </p>

<pre>
...
&lt;devices&gt;
  &lt;smartcard mode='host'/&gt;
  &lt;smartcard mode='host-certificates'&gt;
    &lt;certificate&gt;cert1&lt;/certificate&gt;
    &lt;certificate&gt;cert2&lt;/certificate&gt;
    &lt;certificate&gt;cert3&lt;/certificate&gt;
    &lt;database&gt;/etc/pki/nssdb/&lt;/database&gt;
  &lt;/smartcard&gt;
  &lt;smartcard mode='passthrough' type='tcp'&gt;
    &lt;source mode='bind' host='127.0.0.1' service='2001'/&gt;
    &lt;protocol type='raw'/&gt;
    &lt;address type='ccid' controller='0' slot='0'/&gt;
  &lt;/smartcard&gt;
  &lt;smartcard mode='passthrough' type='spicevmc'/&gt;
&lt;/devices&gt;
...
</pre>

    <p>
      The <code>&lt;smartcard&gt;</code> element has a mandatory
      attribute <code>mode</code>.  The following modes are supported;
      in each mode, the guest sees a device on its USB bus that
      behaves like a physical USB CCID (Chip/Smart Card Interface
      Device) card.
    </p>

    <dl>
      <dt><code>host</code></dt>
      <dd>The simplest operation, where the hypervisor relays all
      requests from the guest into direct access to the host's
      smartcard via NSS.  No other attributes or sub-elements are
      required.  See below about the use of an
      optional <code>&lt;address&gt;</code> sub-element.</dd>

      <dt><code>host-certificates</code></dt>
      <dd>Rather than requiring a smartcard to be plugged into the
      host, it is possible to provide three NSS certificate names
      residing in a database on the host.  These certificates can be
      generated via the command <code>certutil -d /etc/pki/nssdb -x -t
      CT,CT,CT -S -s CN=cert1 -n cert1</code>, and the resulting three
      certificate names must be supplied as the content of each of
      three <code>&lt;certificate&gt;</code> sub-elements.  An
      additional sub-element <code>&lt;database&gt;</code> can specify
      the absolute path to an alternate directory (matching
      the <code>-d</code> option of the <code>certutil</code> command
      when creating the certificates); if not present, it defaults to
      /etc/pki/nssdb.</dd>

      <dt><code>passthrough</code></dt>
      <dd>Rather than having the hypervisor directly communicate with
      the host, it is possible to tunnel all requests through a
      secondary character device to a third-party provider (which may
      in turn be talking to a smartcard or using three certificate
      files).  In this mode of operation, an additional
      attribute <code>type</code> is required, matching one of the
      supported <a href="#elementsConsole">serial device</a> types, to
      describe the host side of the tunnel; <code>type='tcp'</code>
      or <code>type='spicevmc'</code> (which uses the smartcard
      channel of a <a href="#elementsGraphics">SPICE graphics
      device</a>) are typical.  Further sub-elements, such
      as <code>&lt;source&gt;</code>, may be required according to the
      given type, although a <code>&lt;target&gt;</code> sub-element
      is not required (since the consumer of the character device is
      the hypervisor itself, rather than a device visible in the
      guest).</dd>
    </dl>

    <p>
      Each mode supports an optional
      sub-element <code>&lt;address&gt;</code>, which fine-tunes the
      correlation between the smartcard and a ccid bus
      controller, <a href="#elementsAddress">documented above</a>.
      For now, qemu only supports at most one
      smartcard, with an address of bus=0 slot=0.
    </p>

    <h4><a id="elementsNICS">Network interfaces</a></h4>

<pre>
...
&lt;devices&gt;
  &lt;interface type='direct' trustGuestRxFilters='yes'&gt;
    &lt;source dev='eth0'/&gt;
    &lt;mac address='52:54:00:5d:c7:9e'/&gt;
    &lt;boot order='1'/&gt;
    &lt;rom bar='off'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      There are several possibilities for specifying a network
      interface visible to the guest.  Each subsection below provides
      more details about common setup options.
    </p>
    <p>
      <span class="since">Since 1.2.10</span>),
      the <code>interface</code> element
      property <code>trustGuestRxFilters</code> provides the
      capability for the host to detect and trust reports from the
      guest regarding changes to the interface mac address and receive
      filters by setting the attribute to <code>yes</code>. The default
      setting for the attribute is <code>no</code> for security
      reasons and support depends on the guest network device model as
      well as the type of connection on the host - currently it is
      only supported for the virtio device model and for macvtap
      connections on the host.
    </p>
    <p>
      Each <code>&lt;interface&gt;</code> element has an
      optional <code>&lt;address&gt;</code> sub-element that can tie
      the interface to a particular pci slot, with
      attribute <code>type='pci'</code>
      as <a href="#elementsAddress">documented above</a>.
    </p>

    <h5><a id="elementsNICSVirtual">Virtual network</a></h5>

    <p>
      <strong><em>
      This is the recommended config for general guest connectivity on
      hosts with dynamic / wireless networking configs (or multi-host
      environments where the host hardware details are described
      separately in a <code>&lt;network&gt;</code>
      definition <span class="since">Since 0.9.4</span>).
      </em></strong>
    </p>

    <p>

      Provides a connection whose details are described by the named
      network definition. Depending on the virtual network's "forward
      mode" configuration, the network may be totally isolated
      (no <code>&lt;forward&gt;</code> element given), NAT'ing to an
      explicit network device or to the default route
      (<code>&lt;forward mode='nat'&gt;</code>), routed with no NAT
      (<code>&lt;forward mode='route'/&gt;</code>), or connected
      directly to one of the host's network interfaces (via macvtap)
      or bridge devices ((<code>&lt;forward
      mode='bridge|private|vepa|passthrough'/&gt;</code> <span class="since">Since
      0.9.4</span>)
    </p>
    <p>
      For networks with a forward mode of bridge, private, vepa, and
      passthrough, it is assumed that the host has any necessary DNS
      and DHCP services already setup outside the scope of libvirt. In
      the case of isolated, nat, and routed networks, DHCP and DNS are
      provided on the virtual network by libvirt, and the IP range can
      be determined by examining the virtual network config with
      '<code>virsh net-dumpxml [networkname]</code>'. There is one
      virtual network called 'default' setup out of the box which does
      NAT'ing to the default route and has an IP range
      of <code>192.168.122.0/255.255.255.0</code>. Each guest will
      have an associated tun device created with a name of vnetN,
      which can also be overridden with the &lt;target&gt; element
      (see
      <a href="#elementsNICSTargetOverride">overriding the target element</a>).
    </p>
    <p>
      When the source of an interface is a network,
      a <code>portgroup</code> can be specified along with the name of
      the network; one network may have multiple portgroups defined,
      with each portgroup containing slightly different configuration
      information for different classes of network
      connections. <span class="since">Since 0.9.4</span>.
    </p>
    <p>
      When a guest is running an interface of type <code>network</code>
      may include a <code>portid</code> attribute. This provides the UUID
      of an associated virNetworkPortPtr object that records the association
      between the domain interface and the network. This attribute is
      read-only since port objects are create and deleted automatically
      during startup and shutdown. <span class="since">Since 5.1.0</span>
    </p>
    <p>
      Also, similar to <code>direct</code> network connections
      (described below), a connection of type <code>network</code> may
      specify a <code>virtualport</code> element, with configuration
      data to be forwarded to a vepa (802.1Qbg) or 802.1Qbh compliant
      switch (<span class="since">Since 0.8.2</span>), or to an
      Open vSwitch virtual switch (<span class="since">Since
      0.9.11</span>).
    </p>
    <p>
      Since the actual type of switch may vary depending on the
      configuration in the <code>&lt;network&gt;</code> on the host,
      it is acceptable to omit the virtualport <code>type</code>
      attribute, and specify attributes from multiple different
      virtualport types (and also to leave out certain attributes); at
      domain startup time, a complete <code>&lt;virtualport&gt;</code>
      element will be constructed by merging together the type and
      attributes defined in the network and the portgroup referenced
      by the interface. The newly-constructed virtualport is a combination
      of them. The attributes from lower virtualport can't make change
      on the ones defined in higher virtualport.
      Interface takes the highest priority, portgroup is lowest priority.
      (<span class="since">Since 0.10.0</span>). For example, in order
      to work properly with both an 802.1Qbh switch and an Open vSwitch
      switch, you may choose to specify no type, but both
      a <code>profileid</code> (in case the switch is 802.1Qbh) and
      an <code>interfaceid</code> (in case the switch is Open vSwitch)
      (you may also omit the other attributes, such as managerid,
      typeid, or profileid, to be filled in from the
      network's <code>&lt;virtualport&gt;</code>). If you want to
      limit a guest to connecting only to certain types of switches,
      you can specify the virtualport type, but still omit some/all of
      the parameters - in this case if the host's network has a
      different type of virtualport, connection of the interface will
      fail.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
  &lt;/interface&gt;
  ...
  &lt;interface type='network'&gt;
    &lt;source network='default' portgroup='engineering'/&gt;
    &lt;target dev='vnet7'/&gt;
    &lt;mac address="00:11:22:33:44:55"/&gt;
    &lt;virtualport&gt;
      &lt;parameters instanceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSBridge">Bridge to LAN</a></h5>

    <p>
      <strong><em>
      This is the recommended config for general guest connectivity on
      hosts with static wired networking configs.
      </em></strong>
    </p>

    <p>
      Provides a bridge from the VM directly to the LAN. This assumes
      there is a bridge device on the host which has one or more of the hosts
      physical NICs enslaved. The guest VM will have an associated tun device
      created with a name of vnetN, which can also be overridden with the
      &lt;target&gt; element (see
      <a href="#elementsNICSTargetOverride">overriding the target element</a>).
      The tun device will be enslaved to the bridge. The IP range / network
      configuration is whatever is used on the LAN. This provides the guest VM
      full incoming &amp; outgoing net access just like a physical machine.
    </p>
    <p>
      On Linux systems, the bridge device is normally a standard Linux
      host bridge. On hosts that support Open vSwitch, it is also
      possible to connect to an Open vSwitch bridge device by adding
      a <code>&lt;virtualport type='openvswitch'/&gt;</code> to the
      interface definition.  (<span class="since">Since
      0.9.11</span>). The Open vSwitch type virtualport accepts two
      parameters in its <code>&lt;parameters&gt;</code> element -
      an <code>interfaceid</code> which is a standard uuid used to
      uniquely identify this particular interface to Open vSwitch (if
      you do not specify one, a random interfaceid will be generated
      for you when you first define the interface), and an
      optional <code>profileid</code> which is sent to Open vSwitch as
      the interfaces "port-profile".
    </p>
<pre>
...
&lt;devices&gt;
  ...
  &lt;interface type='bridge'&gt;
    &lt;source bridge='br0'/&gt;
  &lt;/interface&gt;
  &lt;interface type='bridge'&gt;
    &lt;source bridge='br1'/&gt;
    &lt;target dev='vnet7'/&gt;
    &lt;mac address="00:11:22:33:44:55"/&gt;
  &lt;/interface&gt;
  &lt;interface type='bridge'&gt;
    &lt;source bridge='ovsbr'/&gt;
    &lt;virtualport type='openvswitch'&gt;
      &lt;parameters profileid='menial' interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
  ...
&lt;/devices&gt;
...</pre>

    <p>
      On hosts that support Open vSwitch on the kernel side and have the
      Midonet Host Agent configured, it is also possible to connect to the
      'midonet' bridge device by adding a
      <code>&lt;virtualport type='midonet'/&gt;</code> to the
      interface definition.  (<span class="since">Since
      1.2.13</span>). The Midonet virtualport type requires an
      <code>interfaceid</code> attribute in its
      <code>&lt;parameters&gt;</code> element. This interface id is the UUID
      that specifies which port in the virtual network topology will be bound
      to the interface.
    </p>
<pre>
...
&lt;devices&gt;
  ...
  &lt;interface type='bridge'&gt;
    &lt;source bridge='br0'/&gt;
  &lt;/interface&gt;
  &lt;interface type='bridge'&gt;
    &lt;source bridge='br1'/&gt;
    &lt;target dev='vnet7'/&gt;
    &lt;mac address="00:11:22:33:44:55"/&gt;
  &lt;/interface&gt;
  &lt;interface type='bridge'&gt;
    &lt;source bridge='midonet'/&gt;
    &lt;virtualport type='midonet'&gt;
      &lt;parameters interfaceid='0b2d64da-3d0e-431e-afdd-804415d6ebbb'/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
  ...
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSSlirp">Userspace SLIRP stack</a></h5>

    <p>
      Provides a virtual LAN with NAT to the outside world. The virtual
      network has DHCP &amp; DNS services and will give the guest VM addresses
      starting from <code>10.0.2.15</code>. The default router will be
      <code>10.0.2.2</code> and the DNS server will be <code>10.0.2.3</code>.
      This networking is the only option for unprivileged users who need their
      VMs to have outgoing access. <span class="since">Since 3.8.0</span>
      it is possible to override the default network address by
      including an <code>ip</code> element specifying an IPv4
      address in its one mandatory attribute, <code>address</code>.
      Optionally, a second <code>ip</code> element with a
      <code>family</code> attribute set to "ipv6" can be
      specified to add an IPv6 address to the interface.
      <code>address</code>. Optionally, address
      <code>prefix</code> can be specified.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='user'/&gt;
  ...
  &lt;interface type='user'&gt;
    &lt;mac address="00:11:22:33:44:55"/&gt;
    &lt;ip family='ipv4' address='172.17.2.0' prefix='24'/&gt;
    &lt;ip family='ipv6' address='2001:db8:ac10:fd01::' prefix='64'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>


    <h5><a id="elementsNICSEthernet">Generic ethernet connection</a></h5>

    <p>
      Provides a means for the administrator to execute an arbitrary script
      to connect the guest's network to the LAN. The guest will have a tun
      device created with a name of vnetN, which can also be overridden with the
      &lt;target&gt; element. After creating the tun device a shell script will
      be run which is expected to do whatever host network integration is
      required. By default this script is called /etc/qemu-ifup but can be
      overridden.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='ethernet'/&gt;
  ...
  &lt;interface type='ethernet'&gt;
    &lt;target dev='vnet7'/&gt;
    &lt;script path='/etc/qemu-ifup-mynet'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSDirect">Direct attachment to physical interface</a></h5>

    <p>
      Provides direct attachment of the virtual machine's NIC to the given
      physical interface of the host.
      <span class="since">Since 0.7.7 (QEMU and KVM only)</span><br/>
      This setup requires the Linux macvtap
      driver to be available. <span class="since">(Since Linux 2.6.34.)</span>
      One of the modes 'vepa'
      ( <a href="http://www.ieee802.org/1/files/public/docs2009/new-evb-congdon-vepa-modular-0709-v01.pdf">
      'Virtual Ethernet Port Aggregator'</a>), 'bridge' or 'private'
      can be chosen for the operation mode of the macvtap device, 'vepa'
      being the default mode. The individual modes cause the delivery of
      packets to behave as follows:
    </p>
    <p>
      If the model type is set to <code>virtio</code> and
      interface's <code>trustGuestRxFilters</code> attribute is set
      to <code>yes</code>, changes made to the interface mac address,
      unicast/multicast receive filters, and vlan settings in the
      guest will be monitored and propagated to the associated macvtap
      device on the host (<span class="since">Since
      1.2.10</span>). If <code>trustGuestRxFilters</code> is not set,
      or is not supported for the device model in use, an attempted
      change to the mac address originating from the guest side will
      result in a non-working network connection.
    </p>

    <dl>
      <dt><code>vepa</code></dt>
      <dd>All VMs' packets are sent to the external bridge. Packets
      whose destination is a VM on the same host as where the
      packet originates from are sent back to the host by the VEPA
      capable bridge (today's bridges are typically not VEPA capable).</dd>
      <dt><code>bridge</code></dt>
      <dd>Packets whose destination is on the same host as where they
      originate from are directly delivered to the target macvtap device.
      Both origin and destination devices need to be in bridge mode
      for direct delivery. If either one of them is in <code>vepa</code> mode,
      a VEPA capable bridge is required.</dd>
      <dt><code>private</code></dt>
      <dd>All packets are sent to the external bridge and will only be
      delivered to a target VM on the same host if they are sent through an
      external router or gateway and that device sends them back to the
      host. This procedure is followed if either the source or destination
      device is in <code>private</code> mode.</dd>
      <dt><code>passthrough</code></dt>
      <dd>This feature attaches a virtual function of a SRIOV capable
      NIC directly to a VM without losing the migration capability.
      All packets are sent to the VF/IF of the configured network device.
      Depending on the capabilities of the device additional prerequisites or
      limitations may apply; for example, on Linux this requires
      kernel 2.6.38 or newer. <span class="since">Since 0.9.2</span></dd>
    </dl>

<pre>
...
&lt;devices&gt;
  ...
  &lt;interface type='direct' trustGuestRxFilters='no'&gt;
    &lt;source dev='eth0' mode='vepa'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      The network access of direct attached virtual machines can be
      managed by the hardware switch to which the physical interface
      of the host machine is connected to.
    </p>
    <p>
      The interface can have additional parameters as shown below,
      if the switch is conforming to the IEEE 802.1Qbg standard.
      The parameters of the virtualport element are documented in more detail
      in the IEEE 802.1Qbg standard. The values are network specific and
      should be provided by the network administrator. In 802.1Qbg terms,
      the Virtual Station Interface (VSI) represents the virtual interface
      of a virtual machine. <span class="since">Since 0.8.2</span>
    </p>
    <p>
      Please note that IEEE 802.1Qbg requires a non-zero value for the
      VLAN ID.
    </p>
    <dl>
      <dt><code>managerid</code></dt>
      <dd>The VSI Manager ID identifies the database containing the VSI type
        and instance definitions. This is an integer value and the
        value 0 is reserved.</dd>
      <dt><code>typeid</code></dt>
      <dd>The VSI Type ID identifies a VSI type characterizing the network
        access. VSI types are typically managed by network administrator.
        This is an integer value.
      </dd>
      <dt><code>typeidversion</code></dt>
      <dd>The VSI Type Version allows multiple versions of a VSI Type.
        This is an integer value.
      </dd>
      <dt><code>instanceid</code></dt>
      <dd>The VSI Instance ID Identifier is generated when a VSI instance
        (i.e. a virtual interface of a virtual machine) is created.
        This is a globally unique identifier.
      </dd>
    </dl>
<pre>
...
&lt;devices&gt;
  ...
  &lt;interface type='direct'&gt;
    &lt;source dev='eth0.2' mode='vepa'/&gt;
    &lt;virtualport type="802.1Qbg"&gt;
      &lt;parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      The interface can have additional parameters as shown below
      if the switch is conforming to the IEEE 802.1Qbh standard.
      The values are network specific and should be provided by the
      network administrator. <span class="since">Since 0.8.2</span>
    </p>
    <dl>
      <dt><code>profileid</code></dt>
      <dd>The profile ID contains the name of the port profile that is to
        be applied to this interface.  This name is resolved by the port
        profile database into the network parameters from the port profile,
        and those network parameters will be applied to this interface.
      </dd>
    </dl>
  <pre>
...
&lt;devices&gt;
  ...
  &lt;interface type='direct'&gt;
    &lt;source dev='eth0' mode='private'/&gt;
    &lt;virtualport type='802.1Qbh'&gt;
      &lt;parameters profileid='finance'/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...
</pre>


    <h5><a id="elementsNICSHostdev">PCI Passthrough</a></h5>

    <p>
      A PCI network device (specified by the &lt;source&gt; element)
      is directly assigned to the guest using generic device
      passthrough, after first optionally setting the device's MAC
      address to the configured value, and associating the device with
      an 802.1Qbh capable switch using an optionally specified
      &lt;virtualport&gt; element (see the examples of virtualport
      given above for type='direct' network devices). Note that - due
      to limitations in standard single-port PCI ethernet card driver
      design - only SR-IOV (Single Root I/O Virtualization) virtual
      function (VF) devices can be assigned in this manner; to assign
      a standard single-port PCI or PCIe ethernet card to a guest, use
      the traditional &lt;hostdev&gt; device definition and
      <span class="since">Since 0.9.11</span>
    </p>

    <p>
      To use VFIO device assignment rather than traditional/legacy KVM
      device assignment (VFIO is a new method of device assignment
      that is compatible with UEFI Secure Boot), a type='hostdev'
      interface can have an optional <code>driver</code> sub-element
      with a <code>name</code> attribute set to "vfio". To use legacy
      KVM device assignment you can set <code>name</code> to "kvm" (or
      simply omit the <code>&lt;driver&gt;</code> element, since "kvm"
      is currently the default).
      <span class="since">Since 1.0.5 (QEMU and KVM only, requires kernel 3.6 or newer)</span>
    </p>

    <p>
      Note that this "intelligent passthrough" of network devices is
      very similar to the functionality of a standard &lt;hostdev&gt;
      device, the difference being that this method allows specifying
      a MAC address and &lt;virtualport&gt; for the passed-through
      device. If these capabilities are not required, if you have a
      standard single-port PCI, PCIe, or USB network card that doesn't
      support SR-IOV (and hence would anyway lose the configured MAC
      address during reset after being assigned to the guest domain),
      or if you are using a version of libvirt older than 0.9.11, you
      should use standard &lt;hostdev&gt; to assign the device to the
      guest instead of &lt;interface type='hostdev'/&gt;.
    </p>

    <p>
      Similar to the functionality of a standard &lt;hostdev&gt; device,
      when <code>managed</code> is "yes", it is detached from the host
      before being passed on to the guest, and reattached to the host
      after the guest exits. If <code>managed</code> is omitted or "no",
      the user is responsible to call <code>virNodeDeviceDettach</code>
      (or <code>virsh nodedev-detach</code>) before starting the guest
      or hot-plugging the device, and <code>virNodeDeviceReAttach</code>
      (or <code>virsh nodedev-reattach</code>) after hot-unplug or
      stopping the guest.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='hostdev' managed='yes'&gt;
    &lt;driver name='vfio'/&gt;
    &lt;source&gt;
      &lt;address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/&gt;
    &lt;/source&gt;
    &lt;mac address='52:54:00:6d:90:02'/&gt;
    &lt;virtualport type='802.1Qbh'&gt;
      &lt;parameters profileid='finance'/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>


    <h5><a id="elementsNICSMulticast">Multicast tunnel</a></h5>

    <p>
      A multicast group is setup to represent a virtual network. Any VMs
      whose network devices are in the same multicast group can talk to each
      other even across hosts. This mode is also available to unprivileged
      users. There is no default DNS or DHCP support and no outgoing network
      access. To provide outgoing network access, one of the VMs should have a
      2nd NIC which is connected to one of the first 4 network types and do the
      appropriate routing. The multicast protocol is compatible with that used
      by user mode linux guests too. The source address used must be from the
      multicast address block.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='mcast'&gt;
    &lt;mac address='52:54:00:6d:90:01'/&gt;
    &lt;source address='230.0.0.1' port='5558'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSTCP">TCP tunnel</a></h5>

    <p>
      A TCP client/server architecture provides a virtual network. One VM
      provides the server end of the network, all other VMS are configured as
      clients. All network traffic is routed between the VMs via the server.
      This mode is also available to unprivileged users. There is no default
      DNS or DHCP support and no outgoing network access. To provide outgoing
      network access, one of the VMs should have a 2nd NIC which is connected
      to one of the first 4 network types and do the appropriate routing.</p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='server'&gt;
    &lt;mac address='52:54:00:22:c9:42'/&gt;
    &lt;source address='192.168.0.1' port='5558'/&gt;
  &lt;/interface&gt;
  ...
  &lt;interface type='client'&gt;
    &lt;mac address='52:54:00:8b:c9:51'/&gt;
    &lt;source address='192.168.0.1' port='5558'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSUDP">UDP unicast tunnel</a></h5>

    <p>
    A UDP unicast architecture provides a virtual network which enables
    connections between QEMU instances using QEMU's UDP infrastructure.

    The xml "source" address is the endpoint address to which the UDP socket
    packets will be sent from the host running QEMU.
    The xml "local" address is the address of the interface from which the
    UDP socket packets will originate from the QEMU host.
    <span class="since">Since 1.2.20</span></p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='udp'&gt;
    &lt;mac address='52:54:00:22:c9:42'/&gt;
    &lt;source address='127.0.0.1' port='11115'&gt;
      &lt;local address='127.0.0.1' port='11116'/&gt;
    &lt;/source&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSModel">Setting the NIC model</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet1'/&gt;
    <b>&lt;model type='ne2k_pci'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      For hypervisors which support this, you can set the model of
      emulated network interface card.
    </p>

    <p>
      The values for <code>type</code> aren't defined specifically by
      libvirt, but by what the underlying hypervisor supports (if
      any).  For QEMU and KVM you can get a list of supported models
      with these commands:
    </p>

<pre>
qemu -net nic,model=? /dev/null
qemu-kvm -net nic,model=? /dev/null
</pre>

    <p>
      Typical values for QEMU and KVM include:
      ne2k_isa i82551 i82557b i82559er ne2k_pci pcnet rtl8139 e1000 virtio.
      <span class="since">Since 5.2.0</span>, <code>virtio-transitional</code>
      and <code>virtio-non-transitional</code> values are supported.
      See <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
      for more details.
    </p>

    <h5><a id="elementsDriverBackendOptions">Setting NIC driver-specific options</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet1'/&gt;
    &lt;model type='virtio'/&gt;
    <b>&lt;driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5' rx_queue_size='256' tx_queue_size='256'&gt;
      &lt;host csum='off' gso='off' tso4='off' tso6='off' ecn='off' ufo='off' mrg_rxbuf='off'/&gt;
      &lt;guest csum='off' tso4='off' tso6='off' ecn='off' ufo='off'/&gt;
    &lt;/driver&gt;
    </b>&lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      Some NICs may have tunable driver-specific options. These are
      set as attributes of the <code>driver</code> sub-element of the
      interface definition. Currently the following attributes are
      available for the <code>"virtio"</code> NIC driver:
    </p>

    <dl>
      <dt><code>name</code></dt>
      <dd>
        The optional <code>name</code> attribute forces which type of
        backend driver to use. The value can be either 'qemu' (a
        user-space backend) or 'vhost' (a kernel backend, which
        requires the vhost module to be provided by the kernel); an
        attempt to require the vhost driver without kernel support
        will be rejected.  If this attribute is not present, then the
        domain defaults to 'vhost' if present, but silently falls back
        to 'qemu' without error.
        <span class="since">Since 0.8.8 (QEMU and KVM only)</span>
      </dd>
      <dd>
        For interfaces of type='hostdev' (PCI passthrough devices)
        the <code>name</code> attribute can optionally be set to
        "vfio" or "kvm". "vfio" tells libvirt to use VFIO device
        assignment rather than traditional KVM device assignment (VFIO
        is a new method of device assignment that is compatible with
        UEFI Secure Boot), and "kvm" tells libvirt to use the legacy
        device assignment performed directly by the kvm kernel module
        (the default is currently "kvm", but is subject to change).
        <span class="since">Since 1.0.5 (QEMU and KVM only, requires
        kernel 3.6 or newer)</span>
      </dd>
      <dd>
        For interfaces of type='vhostuser', the <code>name</code>
        attribute is ignored. The backend driver used is always
        vhost-user.
      </dd>

      <dt><code>txmode</code></dt>
      <dd>
        The <code>txmode</code> attribute specifies how to handle
        transmission of packets when the transmit buffer is full. The
        value can be either 'iothread' or 'timer'.
        <span class="since">Since 0.8.8 (QEMU and KVM only)</span><br/><br/>

        If set to 'iothread', packet tx is all done in an iothread in
        the bottom half of the driver (this option translates into
        adding "tx=bh" to the qemu commandline -device virtio-net-pci
        option).<br/><br/>

        If set to 'timer', tx work is done in qemu, and if there is
        more tx data than can be sent at the present time, a timer is
        set before qemu moves on to do other things; when the timer
        fires, another attempt is made to send more data.<br/><br/>

        The resulting difference, according to the qemu developer who
        added the option is: "bh makes tx more asynchronous and reduces
        latency, but potentially causes more processor bandwidth
        contention since the CPU doing the tx isn't necessarily the
        CPU where the guest generated the packets."<br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt><code>ioeventfd</code></dt>
      <dd>
        This optional attribute allows users to set
        <a href='https://patchwork.kernel.org/patch/43390/'>
        domain I/O asynchronous handling</a> for interface device.
        The default is left to the discretion of the hypervisor.
        Accepted values are "on" and "off". Enabling this allows
        qemu to execute VM while a separate thread handles I/O.
        Typically guests experiencing high system CPU utilization
        during I/O will benefit from this. On the other hand,
        on overloaded host it could increase guest I/O latency.
        <span class="since">Since 0.9.3 (QEMU and KVM only)</span><br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt><code>event_idx</code></dt>
      <dd>
        The <code>event_idx</code> attribute controls some aspects of
        device event processing. The value can be either 'on' or 'off'
        - if it is on, it will reduce the number of interrupts and
        exits for the guest. The default is determined by QEMU;
        usually if the feature is supported, default is on. In case
        there is a situation where this behavior is suboptimal, this
        attribute provides a way to force the feature off.
        <span class="since">Since 0.9.5 (QEMU and KVM only)</span><br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt><code>queues</code></dt>
      <dd>
        The optional <code>queues</code> attribute controls the number
        of queues to be used for either
        <a href="https://www.linux-kvm.org/page/Multiqueue"> Multiqueue
        virtio-net</a> or <a href="#elementVhostuser">vhost-user</a> network
        interfaces.  Use of multiple packet processing queues requires the
        interface having the <code>&lt;model type='virtio'/&gt;</code>
        element.  Each queue will potentially be handled by a different
        processor, resulting in much higher throughput.
        <span class="since">virtio-net since 1.0.6 (QEMU and KVM only)</span>
        <span class="since">vhost-user since 1.2.17 (QEMU and KVM only)</span>
      </dd>
      <dt><code>rx_queue_size</code></dt>
      <dd>
        The optional <code>rx_queue_size</code> attribute controls
        the size of virtio ring for each queue as described above.
        The default value is hypervisor dependent and may change
        across its releases. Moreover, some hypervisors may pose
        some restrictions on actual value. For instance, latest
        QEMU (as of 2016-09-01) requires value to be a power of two
        from [256, 1024] range.
        <span class="since">Since 2.3.0 (QEMU and KVM only)</span><br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt><code>tx_queue_size</code></dt>
      <dd>
        The optional <code>tx_queue_size</code> attribute controls
        the size of virtio ring for each queue as described above.
        The default value is hypervisor dependent and may change
        across its releases. Moreover, some hypervisors may pose
        some restrictions on actual value. For instance, QEMU
        v2.9  requires value to be a power of two from [256, 1024]
        range. In addition to that, this may work only for a subset of
        interface types, e.g. aforementioned QEMU enables this option
        only for <code>vhostuser</code> type.
        <span class="since">Since 3.7.0 (QEMU and KVM only)</span><br/><br/>

        <b>In general you should leave this option alone, unless you
        are very certain you know what you are doing.</b>
      </dd>
      <dt>virtio options</dt>
      <dd>
        For virtio interfaces,
        <a href="#elementsVirtio">Virtio-specific options</a> can also be
        set. (<span class="since">Since 3.5.0</span>)
      </dd>
    </dl>
    <p>
      Offloading options for the host and guest can be configured using
      the following sub-elements:
    </p>
    <dl>
      <dt><code>host</code></dt>
      <dd>
        The <code>csum</code>, <code>gso</code>, <code>tso4</code>,
        <code>tso6</code>, <code>ecn</code> and <code>ufo</code>
        attributes with possible values <code>on</code>
        and <code>off</code> can be used to turn off host offloading options.
        By default, the supported offloads are enabled by QEMU.
        <span class="since">Since 1.2.9 (QEMU only)</span>
        The <code>mrg_rxbuf</code> attribute can be used to control
        mergeable rx buffers on the host side. Possible values are
        <code>on</code> (default) and <code>off</code>.
        <span class="since">Since 1.2.13 (QEMU only)</span>
      </dd>
      <dt><code>guest</code></dt>
      <dd>
        The <code>csum</code>, <code>tso4</code>,
        <code>tso6</code>, <code>ecn</code> and <code>ufo</code>
        attributes with possible values <code>on</code>
        and <code>off</code> can be used to turn off guest offloading options.
        By default, the supported offloads are enabled by QEMU.
        <span class="since">Since 1.2.9 (QEMU only)</span>
      </dd>
    </dl>

    <h5><a id="elementsBackendOptions">Setting network backend-specific options</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet1'/&gt;
    &lt;model type='virtio'/&gt;
    <b>&lt;backend tap='/dev/net/tun' vhost='/dev/vhost-net'/&gt;</b>
    &lt;driver name='vhost' txmode='iothread' ioeventfd='on' event_idx='off' queues='5'/&gt;
    <b>&lt;tune&gt;
      &lt;sndbuf&gt;1600&lt;/sndbuf&gt;
    &lt;/tune&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      For tuning the backend of the network, the <code>backend</code> element
      can be used. The <code>vhost</code> attribute can override the default vhost
      device path (<code>/dev/vhost-net</code>) for devices with <code>virtio</code> model.
      The <code>tap</code> attribute overrides the tun/tap device path (default:
      <code>/dev/net/tun</code>) for network and bridge interfaces. This does not work
      in session mode. <span class="since">Since 1.2.9</span>
    </p>
    <p>
      For tap devices there is also <code>sndbuf</code> element which can
      adjust the size of send buffer in the host. <span class="since">Since
      0.8.8</span>
    </p>
    <h5><a id="elementsNICSTargetOverride">Overriding the target element</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    <b>&lt;target dev='vnet1'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      If no target is specified, certain hypervisors will
      automatically generate a name for the created tun device. This
      name can be manually specified, however the name <i>should not
      start with either 'vnet', 'vif', 'macvtap', or 'macvlan'</i>,
      which are prefixes reserved by libvirt and certain hypervisors.
      Manually specified targets using these prefixes may be ignored.
    </p>

    <p>
      Note that for LXC containers, this defines the name of the interface
      on the host side. <span class="since">Since 1.2.7</span>, to define
      the name of the device on the guest side, the <code>guest</code>
      element should be used, as in the following snippet:
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    <b>&lt;guest dev='myeth'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <h5><a id="elementsNICSBoot">Specifying boot order</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet1'/&gt;
    <b>&lt;boot order='1'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      For hypervisors which support this, you can set a specific NIC to
      be used for network boot. The <code>order</code> attribute determines
      the order in which devices will be tried during boot sequence. The
      per-device <code>boot</code> elements cannot be used together with
      general boot elements in
      <a href="#elementsOSBIOS">BIOS bootloader</a> section.
      <span class="since">Since 0.8.8</span>
    </p>

    <h5><a id="elementsNICSROM">Interface ROM BIOS configuration</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet1'/&gt;
    <b>&lt;rom bar='on' file='/etc/fake/boot.bin'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      For hypervisors which support this, you can change how a PCI Network
      device's ROM is presented to the guest. The <code>bar</code>
      attribute can be set to "on" or "off", and determines whether
      or not the device's ROM will be visible in the guest's memory
      map. (In PCI documentation, the "rombar" setting controls the
      presence of the Base Address Register for the ROM). If no rom
      bar is specified, the qemu default will be used (older
      versions of qemu used a default of "off", while newer qemus
      have a default of "on").
      The optional <code>file</code> attribute is used to point to a
      binary file to be presented to the guest as the device's ROM
      BIOS. This can be useful to provide an alternative boot ROM for a
      network device.
      <span class="since">Since 0.9.10 (QEMU and KVM only)</span>.
    </p>
    <h5><a id="elementDomain">Setting up a network backend in a driver domain</a></h5>
<pre>
...
&lt;devices&gt;
  ...
  &lt;interface type='bridge'&gt;
    &lt;source bridge='br0'/&gt;
    <b>&lt;backenddomain name='netvm'/&gt;</b>
  &lt;/interface&gt;
  ...
&lt;/devices&gt;
...</pre>

    <p>
      The optional <code>backenddomain</code> element allows specifying a
      backend domain (aka driver domain) for the interface. Use the
      <code>name</code> attribute to specify the backend domain name. You
      can use it to create a direct network link between domains (so data
      will not go through host system). Use with type 'ethernet' to create
      plain network link, or with type 'bridge' to connect to a bridge inside
      the backend domain.
      <span class="since">Since 1.2.13 (Xen only)</span>
    </p>

    <h5><a id="elementQoS">Quality of service</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet0'/&gt;
    <b>&lt;bandwidth&gt;
      &lt;inbound average='1000' peak='5000' floor='200' burst='1024'/&gt;
      &lt;outbound average='128' peak='256' burst='256'/&gt;
    &lt;/bandwidth&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      This part of interface XML provides setting quality of service. Incoming
      and outgoing traffic can be shaped independently.
      The <code>bandwidth</code> element and its child elements are described
      in the <a href="formatnetwork.html#elementQoS">QoS</a> section of
      the Network XML.
    </p>

    <h5><a id="elementVlanTag">Setting VLAN tag (on supported network types only)</a></h5>

<pre>
...
&lt;devices&gt;
  &lt;interface type='bridge'&gt;
    <b>&lt;vlan&gt;</b>
      <b>&lt;tag id='42'/&gt;</b>
    <b>&lt;/vlan&gt;</b>
    &lt;source bridge='ovsbr0'/&gt;
    &lt;virtualport type='openvswitch'&gt;
      &lt;parameters interfaceid='09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f'/&gt;
    &lt;/virtualport&gt;
  &lt;/interface&gt;
  &lt;interface type='bridge'&gt;
    <b>&lt;vlan trunk='yes'&gt;</b>
      <b>&lt;tag id='42'/&gt;</b>
      <b>&lt;tag id='123' nativeMode='untagged'/&gt;</b>
    <b>&lt;/vlan&gt;</b>
    ...
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      If (and only if) the network connection used by the guest
      supports VLAN tagging transparent to the guest, an
      optional <code>&lt;vlan&gt;</code> element can specify one or
      more VLAN tags to apply to the guest's network
      traffic <span class="since">Since 0.10.0</span>. Network
      connections that support guest-transparent VLAN tagging include
      1) type='bridge' interfaces connected to an Open vSwitch bridge
      <span class="since">Since 0.10.0</span>, 2) SRIOV Virtual
      Functions (VF) used via type='hostdev' (direct device
      assignment) <span class="since">Since 0.10.0</span>, and 3)
      SRIOV VFs used via type='direct' with mode='passthrough'
      (macvtap "passthru" mode) <span class="since">Since
      1.3.5</span>. All other connection types, including standard
      linux bridges and libvirt's own virtual networks, <b>do not</b>
      support it. 802.1Qbh (vn-link) and 802.1Qbg (VEPA) switches
      provide their own way (outside of libvirt) to tag guest traffic
      onto a specific VLAN. Each tag is given in a
      separate <code>&lt;tag&gt;</code> subelement
      of <code>&lt;vlan&gt;</code> (for example: <code>&lt;tag
      id='42'/&gt;</code>). For VLAN trunking of multiple tags (which
      is supported only on Open vSwitch connections),
      multiple <code>&lt;tag&gt;</code> subelements can be specified,
      which implies that the user wants to do VLAN trunking on the
      interface for all the specified tags. In the case that VLAN
      trunking of a single tag is desired, the optional
      attribute <code>trunk='yes'</code> can be added to the toplevel
      <code>&lt;vlan&gt;</code> element to differentiate trunking of a
      single tag from normal tagging.
    </p>
    <p>
      For network connections using Open vSwitch it is also possible
      to configure 'native-tagged' and 'native-untagged' VLAN modes
      <span class="since">Since 1.1.0.</span> This is done with the
      optional <code>nativeMode</code> attribute on
      the <code>&lt;tag&gt;</code> subelement: <code>nativeMode</code>
      may be set to 'tagged' or 'untagged'. The <code>id</code>
      attribute of the <code>&lt;tag&gt;</code> subelement
      containing <code>nativeMode</code> sets which VLAN is considered
      to be the "native" VLAN for this interface, and
      the <code>nativeMode</code> attribute determines whether or not
      traffic for that VLAN will be tagged.
    </p>

    <h5><a id="elementLink">Modifying virtual link state</a></h5>
<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet0'/&gt;
    <b>&lt;link state='down'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      This element provides means of setting state of the virtual network link.
      Possible values for attribute <code>state</code> are <code>up</code> and
      <code>down</code>. If <code>down</code> is specified as the value, the interface
      behaves as if it had the network cable disconnected. Default behavior if this
      element is unspecified is to have the link state <code>up</code>.
      <span class="since">Since 0.9.5</span>
    </p>

    <h5><a id="mtu">MTU configuration</a></h5>
<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet0'/&gt;
    <b>&lt;mtu size='1500'/&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      This element provides means of setting MTU of the virtual network link.
      Currently there is just one attribute <code>size</code> which accepts a
      non-negative integer which specifies the MTU size for the interface.
      <span class="since">Since 3.1.0</span>
    </p>

    <h5><a id="coalesce">Coalesce settings</a></h5>
<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet0'/&gt;
    <b>&lt;coalesce&gt;
      &lt;rx&gt;
        &lt;frames max='7'/&gt;
      &lt;/rx&gt;
    &lt;/coalesce&gt;</b>
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      This element provides means of setting coalesce settings for
      some interface devices (currently only type <code>network</code>
      and <code>bridge</code>.  Currently there is just one attribute,
      <code>max</code>, to tweak, in element <code>frames</code> for
      the <code>rx</code> group, which accepts a non-negative integer
      that specifies the maximum number of packets that will be
      received before an interrupt.
      <span class="since">Since 3.3.0</span>
    </p>

    <h5><a id="ipconfig">IP configuration</a></h5>
<pre>
...
&lt;devices&gt;
  &lt;interface type='network'&gt;
    &lt;source network='default'/&gt;
    &lt;target dev='vnet0'/&gt;
    <b>&lt;ip address='192.168.122.5' prefix='24'/&gt;</b>
    <b>&lt;ip address='192.168.122.5' prefix='24' peer='10.0.0.10'/&gt;</b>
    <b>&lt;route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/&gt;</b>
    <b>&lt;route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/&gt;</b>
  &lt;/interface&gt;
  ...
  &lt;hostdev mode='capabilities' type='net'&gt;
    &lt;source&gt;
      &lt;interface&gt;eth0&lt;/interface&gt;
    &lt;/source&gt;
    <b>&lt;ip address='192.168.122.6' prefix='24'/&gt;</b>
    <b>&lt;route family='ipv4' address='192.168.122.0' prefix='24' gateway='192.168.122.1'/&gt;</b>
    <b>&lt;route family='ipv4' address='192.168.122.8' gateway='192.168.122.1'/&gt;</b>
  &lt;/hostdev&gt;
  ...
&lt;/devices&gt;
...
</pre>

    <p>
      <span class="since">Since 1.2.12</span> network devices and
      hostdev devices with network capabilities can optionally be provided
      one or more IP addresses to set on the network device in the
      guest. Note that some hypervisors or network device types will
      simply ignore them or only use the first one.
      The <code>family</code> attribute can be set to
      either <code>ipv4</code> or <code>ipv6</code>, and the
      <code>address</code> attribute contains the IP address. The
      optional <code>prefix</code> is the number of 1 bits in the
      netmask, and will be automatically set if not specified - for
      IPv4 the default prefix is determined according to the network
      "class" (A, B, or C - see RFC870), and for IPv6 the default
      prefix is 64. The optional <code>peer</code> attribute holds the
      IP address of the other end of a point-to-point network
      device <span class="since">(since 2.1.0)</span>.
    </p>

    <p>
    <span class="since">Since 1.2.12</span> route elements can also be
    added to define IP routes to add in the guest.  The attributes of
    this element are described in the documentation for
    the <code>route</code> element
    in <a href="formatnetwork.html#elementsStaticroute">network
    definitions</a>.  This is used by the LXC driver.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='ethernet'&gt;
    <b>&lt;source/&gt;</b>
      <b>&lt;ip address='192.168.123.1' prefix='24'/&gt;</b>
      <b>&lt;ip address='10.0.0.10' prefix='24' peer='192.168.122.5'/&gt;</b>
      <b>&lt;route family='ipv4' address='192.168.42.0' prefix='24' gateway='192.168.123.4'/&gt;</b>
    <b>&lt;source/&gt;</b>
    ...
  &lt;/interface&gt;
  ...
&lt;/devices&gt;
...
</pre>

    <p>
      <span class="since">Since 2.1.0</span> network devices of type
      "ethernet" can optionally be provided one or more IP addresses
      and one or more routes to set on the <b>host</b> side of the
      network device. These are configured as subelements of
      the <code>&lt;source&gt;</code> element of the interface, and
      have the same attributes as the similarly named elements used to
      configure the guest side of the interface (described above).
    </p>

    <h5><a id="elementVhostuser">vhost-user interface</a></h5>

    <p>
    <span class="since">Since 1.2.7</span> the vhost-user enables the
    communication between a QEMU virtual machine and other userspace process
    using the Virtio transport protocol.  A char dev (e.g. Unix socket) is used
    for the control plane, while the data plane is based on shared memory.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface type='vhostuser'&gt;
    &lt;mac address='52:54:00:3b:83:1a'/&gt;
    &lt;source type='unix' path='/tmp/vhost1.sock' mode='server'/&gt;
    &lt;model type='virtio'/&gt;
  &lt;/interface&gt;
  &lt;interface type='vhostuser'&gt;
    &lt;mac address='52:54:00:3b:83:1b'/&gt;
    &lt;source type='unix' path='/tmp/vhost2.sock' mode='client'&gt;
      &lt;reconnect enabled='yes' timeout='10'/&gt;
    &lt;/source&gt;
    &lt;model type='virtio'/&gt;
    &lt;driver queues='5'/&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      The <code>&lt;source&gt;</code> element has to be specified
      along with the type of char device.
      Currently, only type='unix' is supported, where the path (the
      directory path of the socket) and mode attributes are required.
      Both <code>mode='server'</code> and <code>mode='client'</code>
      are supported.
      vhost-user requires the virtio model type, thus the
      <code>&lt;model&gt;</code> element is mandatory.
      <span class="since">Since 4.1.0</span> the element has an
      optional child element <code>reconnect</code> which
      configures reconnect timeout if the connection is lost. It
      has two attributes <code>enabled</code> (which accepts
      <code>yes</code> and <code>no</code>) and
      <code>timeout</code> which specifies the amount of seconds
      after which hypervisor tries to reconnect.
    </p>

    <h5><a id="elementNwfilter">Traffic filtering with NWFilter</a></h5>

    <p>
    <span class="since">Since 0.8.0</span> an <code>nwfilter</code> profile
    can be assigned to a domain interface, which allows configuring
    traffic filter rules for the virtual machine.

    See the <a href="formatnwfilter.html">nwfilter</a> documentation for more
    complete details.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;interface ...&gt;
    ...
    &lt;filterref filter='clean-traffic'/&gt;
  &lt;/interface&gt;
  &lt;interface ...&gt;
    ...
    &lt;filterref filter='myfilter'&gt;
      &lt;parameter name='IP' value='104.207.129.11'/&gt;
      &lt;parameter name='IP6_ADDR' value='2001:19f0:300:2102::'/&gt;
      &lt;parameter name='IP6_MASK' value='64'/&gt;
      ...
    &lt;/filterref&gt;
  &lt;/interface&gt;
&lt;/devices&gt;
...</pre>

    <p>
      The <code>filter</code> attribute specifies the name of the nwfilter
      to use. Optional <code>&lt;parameter&gt;</code> elements may be
      specified for passing additional info to the nwfilter via the
      <code>name</code> and <code>value</code> attributes. See
      the <a href="formatnwfilter.html#nwfconceptsvars">nwfilter</a>
      docs for info on parameters.
    </p>


    <h4><a id="elementsInput">Input devices</a></h4>

    <p>
      Input devices allow interaction with the graphical framebuffer
      in the guest virtual machine. When enabling the framebuffer, an
      input device is automatically provided. It may be possible to
      add additional devices explicitly, for example,
      to provide a graphics tablet for absolute cursor movement.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;input type='mouse' bus='usb'/&gt;
  &lt;input type='keyboard' bus='usb'/&gt;
  &lt;input type='mouse' bus='virtio'/&gt;
  &lt;input type='keyboard' bus='virtio'/&gt;
  &lt;input type='tablet' bus='virtio'/&gt;
  &lt;input type='passthrough' bus='virtio'&gt;
    &lt;source evdev='/dev/input/event1/&gt;
  &lt;/input&gt;
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>input</code></dt>
      <dd>The <code>input</code> element has one mandatory attribute,
        the <code>type</code> whose value can be 'mouse', 'tablet',
        (<span class="since">since 1.2.2</span>) 'keyboard' or
        (<span class="since">since 1.3.0</span>) 'passthrough'.
        The tablet provides absolute cursor movement,
        while the mouse uses relative movement. The optional
        <code>bus</code> attribute can be used to refine the exact device type.
        It takes values "xen" (paravirtualized), "ps2" and "usb" or
        (<span class="since">since 1.3.0</span>) "virtio".</dd>
    </dl>

    <p>
      The <code>input</code> element has an optional
      sub-element <code>&lt;address&gt;</code> which can tie the
      device to a particular PCI
      slot, <a href="#elementsAddress">documented above</a>.
      On S390, <code>address</code> can be used to provide a CCW address for
      an input device (<span class="since">since 4.2.0</span>).

      For type <code>passthrough</code>, the mandatory sub-element <code>source</code>
      must have an <code>evdev</code> attribute containing the absolute path to the
      event device passed through to guests. (KVM only)

      <span class="since">Since 5.2.0</span>, the <code>input</code> element
      accepts a <code>model</code> attribute which has the values 'virtio',
      'virtio-transitional' and 'virtio-non-transitional'. See
      <a href="#elementsVirtioTransitional">Virtio transitional devices</a>
      for more details.
    </p>

    <p>
        The subelement <code>driver</code> can be used to tune the virtio
        options of the device:
        <a href="#elementsVirtio">Virtio-specific options</a> can also be
        set. (<span class="since">Since 3.5.0</span>)
    </p>

    <h4><a id="elementsHub">Hub devices</a></h4>

    <p>
      A hub is a device that expands a single port into several so
      that there are more ports available to connect devices to a host
      system.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;hub type='usb'/&gt;
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>hub</code></dt>
      <dd>The <code>hub</code> element has one mandatory attribute,
        the <code>type</code> whose value can only be 'usb'.</dd>
    </dl>

    <p>
      The <code>hub</code> element has an optional
      sub-element <code>&lt;address&gt;</code>
      with <code>type='usb'</code>which can tie the device to a
      particular controller, <a href="#elementsAddress">documented
      above</a>.
    </p>

    <h4><a id="elementsGraphics">Graphical framebuffers</a></h4>

    <p>
      A graphics device allows for graphical interaction with the
      guest OS. A guest will typically have either a framebuffer
      or a text console configured to allow interaction with the
      admin.
    </p>

<pre>
...
&lt;devices&gt;
  &lt;graphics type='sdl' display=':0.0'/&gt;
  &lt;graphics type='vnc' port='5904' sharePolicy='allow-exclusive'&gt;
    &lt;listen type='address' address='1.2.3.4'/&gt;
  &lt;/graphics&gt;
  &lt;graphics type='rdp' autoport='yes' multiUser='yes' /&gt;
  &lt;graphics type='desktop' fullscreen='yes'/&gt;
  &lt;graphics type='spice'&gt;
    &lt;listen type='network' network='rednet'/&gt;
  &lt;/graphics&gt;
&lt;/devices&gt;
...</pre>

    <dl>
      <dt><code>graphics</code></dt>
      <dd>
        <p>
          The <code>graphics</code> element has a mandatory <code>type</code>
          attribute which takes the value <code>sdl</code>, <code>vnc</code>,
          <code>spice</code>, <code>rdp</code>, <code>desktop</code> or
          <code>egl-headless</code>:
        </p>
        <dl>
          <dt><code>sdl</code></dt>
          <dd>
            <p>
              This displays a window on the host desktop, it can take 3 optional
              arguments: a <code>display</code> attribute for the display to use,
              an <code>xauth</code> attribute for the authentication identifier,
              and an optional <code>fullscreen</code> attribute accepting values
              <code>yes</code> or <code>no</code>.
            </p>

            <p>
              You can use a <code>gl</code> with the <code>enable="yes"</code>
              property to enable OpenGL support in SDL. Likewise you can
              explicitly disable OpenGL support with <code>enable="no"</code>.
            </p>
          </dd>
          <dt><code>vnc</code></dt>
          <dd>
            <p>
              Starts a VNC server. The <code>port</code> attribute specifies
              the TCP port number (with -1 as legacy syntax indicating that it
              should be auto-allocated). The <code>autoport</code> attribute is
              the new preferred syntax for indicating auto-allocation of the TCP
              port to use. The <code>passwd</code> attribute provides a VNC
              password in clear text. If the <code>passwd</code> attribute is
              set to an empty string, then VNC access is disabled. The
              <code>keymap</code> attribute specifies the keymap to use. It is
              possible to set a limit on the validity of the password by giving
              a timestamp <code>passwdValidTo='2010-04-09T15:51:00'</code>
              assumed to be in UTC. The <code>connected</code> attribute allows
              control of connected client during password changes. VNC accepts
              <code>keep</code> value only <span class="since">since 0.9.3</span>.
              NB, this may not be supported by all hypervisors.
            </p>
            <p>
              The optional <code>sharePolicy</code> attribute specifies vnc
              server display sharing policy. <code>allow-exclusive</code> allows