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<h1>Domain capabilities XML format</h1>
<ul><li>
<a href="#Overview">Overview</a>
</li><li>
<a href="#elements">Element and attribute overview</a>
<ul><li>
<a href="#elementsCPUAllocation">CPU Allocation</a>
</li><li>
<a href="#elementsOSBIOS">BIOS bootloader</a>
</li><li>
<a href="#elementsDevices">Devices</a>
<ul><li>
<a href="#elementsDisks">Hard drives, floppy disks, CDROMs</a>
</li><li>
<a href="#elementsHostDev">Host device assignment</a>
</li></ul>
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<h2>
<a name="Overview" shape="rect" id="Overview">Overview</a>
<a class="headerlink" href="#Overview" title="Permalink to this headline">¶</a>
</h2>
<p>Sometimes, when a new domain is to be created it may come handy to know
the capabilities of the hypervisor so the correct combination of devices and
drivers is used. For example, when management application is considering the
mode for a host device's passthrough there are several options depending not
only on host, but on hypervisor in question too. If the hypervisor is qemu
then it needs to be more recent to support VFIO, while legacy KVM is
achievable just fine with older qemus.</p>
<p>The main difference between <a href="html/libvirt-libvirt.html#virConnectGetCapabilities"><code>virConnectGetCapabilities</code></a> and the emulator
capabilities API is, the former one aims more on the host capabilities
(e.g. NUMA topology, security models in effect, etc.) while the latter one
specializes on the hypervisor capabilities.</p>
<p>While the <a href="formatcaps.html" shape="rect">Driver Capabilities</a> provides the
host capabilities (e.g NUMA topology, security models in effect, etc.), the
Domain Capabilities provides the hypervisor specific capabilities for
Management Applications to query and make decisions regarding what to
utilize.</p>
<p>The Domain Capabilities can provide information such as the correct
combination of devices and drivers that are supported. Knowing which host
and hypervisor specific options are available or supported would allow the
management application to choose an appropriate mode for a pass-through
host device as well as which adapter to utilize.</p>
<h2>
<a name="elements" shape="rect" id="elements">Element and attribute overview</a>
<a class="headerlink" href="#elements" title="Permalink to this headline">¶</a>
</h2>
<p> A new query interface was added to the virConnect API's to retrieve the
XML listing of the set of domain capabilities (<span class="since">Since
1.2.7</span>):</p>
<pre xml:space="preserve">
<a href="html/libvirt-libvirt.html#virConnectGetDomainCapabilities"><code>virConnectGetDomainCapabilities</code></a>
</pre>
<p>The root element that emulator capability XML document starts with has
name <code>domainCapabilities</code>. It contains at least four direct
child elements:</p>
<pre xml:space="preserve">
<domainCapabilities>
<path>/usr/bin/qemu-system-x86_64</path>
<domain>kvm</domain>
<machine>pc-i440fx-2.1</machine>
<arch>x86_64</arch>
...
</domainCapabilities>
</pre>
<dl><dt>path</dt><dd>The full path to the emulator binary.</dd><dt>domain</dt><dd>Describes the <a href="formatdomain.html#elements" shape="rect">virtualization
type</a> (or so called domain type).</dd><dt>machine</dt><dd>The domain's <a href="formatdomain.html#elementsOSBIOS" shape="rect">machine
type</a>.</dd><dt>arch</dt><dd>The domain's <a href="formatdomain.html#elementsOSBIOS" shape="rect">
architecture</a>.</dd></dl>
<h3>
<a name="elementsCPUAllocation" shape="rect" id="elementsCPUAllocation">CPU Allocation</a>
<a class="headerlink" href="#elementsCPUAllocation" title="Permalink to this headline">¶</a>
</h3>
<p>Before any devices capability occurs, there might be a info on domain
wide capabilities, e.g. virtual CPUs:</p>
<pre xml:space="preserve">
<domainCapabilities>
...
<vcpu max='255'/>
...
</domainCapabilities>
</pre>
<dl><dt>vcpu</dt><dd>The maximum number of supported virtual CPUs</dd></dl>
<h3>
<a name="elementsOSBIOS" shape="rect" id="elementsOSBIOS">BIOS bootloader</a>
<a class="headerlink" href="#elementsOSBIOS" title="Permalink to this headline">¶</a>
</h3>
<p>Sometimes users might want to tweak some BIOS knobs or use
UEFI. For cases like that, <a href="formatdomain.html#elementsOSBIOS" shape="rect"><code>os</code></a>
element exposes what values can be passed to its children.</p>
<pre xml:space="preserve">
<domainCapabilities>
...
<os supported='yes'>
<loader supported='yes'>
<value>/usr/share/OVMF/OVMF_CODE.fd</value>
<enum name='type'>
<value>rom</value>
<value>pflash</value>
</enum>
<enum name='readonly'>
<value>yes</value>
<value>no</value>
</enum>
</loader>
</os>
...
<domainCapabilities>
</pre>
<p>For the <code>loader</code> element, the following can occur:</p>
<dl><dt>value</dt><dd>List of known loader paths. Currently this is only used
to advertise known locations of OVMF binaries for qemu. Binaries
will only be listed if they actually exist on disk.</dd><dt>type</dt><dd>Whether loader is a typical BIOS (<code>rom</code>) or
an UEFI binary (<code>pflash</code>). This refers to
<code>type</code> attribute of the <loader/>
element.</dd><dt>readonly</dt><dd>Options for the <code>readonly</code> attribute of the
<loader/> element.</dd></dl>
<h3>
<a name="elementsDevices" shape="rect" id="elementsDevices">Devices</a>
<a class="headerlink" href="#elementsDevices" title="Permalink to this headline">¶</a>
</h3>
<p>
The final set of XML elements describe the supported devices and their
capabilities. All devices occur as children of the main
<code>devices</code> element.
</p>
<pre xml:space="preserve">
<domainCapabilities>
...
<devices>
<disk supported='yes'>
<enum name='diskDevice'>
<value>disk</value>
<value>cdrom</value>
<value>floppy</value>
<value>lun</value>
</enum>
...
</disk>
<hostdev supported='no'/>
</devices>
</domainCapabilities>
</pre>
<p>Reported capabilities are expressed as an enumerated list of available
options for each of the element or attribute. For example, the
<disk/> element has an attribute <code>device</code> which can
support the values <code>disk</code>, <code>cdrom</code>,
<code>floppy</code>, or <code>lun</code>.</p>
<h4>
<a name="elementsDisks" shape="rect" id="elementsDisks">Hard drives, floppy disks, CDROMs</a>
<a class="headerlink" href="#elementsDisks" title="Permalink to this headline">¶</a>
</h4>
<p>Disk capabilities are exposed under <code>disk</code> element. For
instance:</p>
<pre xml:space="preserve">
<domainCapabilities>
...
<devices>
<disk supported='yes'>
<enum name='diskDevice'>
<value>disk</value>
<value>cdrom</value>
<value>floppy</value>
<value>lun</value>
</enum>
<enum name='bus'>
<value>ide</value>
<value>fdc</value>
<value>scsi</value>
<value>virtio</value>
<value>xen</value>
<value>usb</value>
<value>uml</value>
<value>sata</value>
<value>sd</value>
</enum>
</disk>
...
</devices>
</domainCapabilities>
</pre>
<dl><dt>diskDevice</dt><dd>Options for the <code>device</code> attribute of the <disk/>
element.</dd><dt>bus</dt><dd>Options for the <code>bus</code> attribute of the <target/>
element for a <disk/>.</dd></dl>
<h4>
<a name="elementsHostDev" shape="rect" id="elementsHostDev">Host device assignment</a>
<a class="headerlink" href="#elementsHostDev" title="Permalink to this headline">¶</a>
</h4>
<p>Some host devices can be passed through to a guest (e.g. USB, PCI and
SCSI). Well, only if the following is enabled:</p>
<pre xml:space="preserve">
<domainCapabilities>
...
<devices>
<hostdev supported='yes'>
<enum name='mode'>
<value>subsystem</value>
<value>capabilities</value>
</enum>
<enum name='startupPolicy'>
<value>default</value>
<value>mandatory</value>
<value>requisite</value>
<value>optional</value>
</enum>
<enum name='subsysType'>
<value>usb</value>
<value>pci</value>
<value>scsi</value>
</enum>
<enum name='capsType'>
<value>storage</value>
<value>misc</value>
<value>net</value>
</enum>
<enum name='pciBackend'>
<value>default</value>
<value>kvm</value>
<value>vfio</value>
<value>xen</value>
</enum>
</hostdev>
</devices>
</domainCapabilities>
</pre>
<dl><dt>mode</dt><dd>Options for the <code>mode</code> attribute of the <hostdev/>
element.</dd><dt>startupPolicy</dt><dd>Options for the <code>startupPolicy</code> attribute of the
<hostdev/> element.</dd><dt>subsysType</dt><dd>Options for the <code>type</code> attribute of the <hostdev/>
element in case of <code>mode="subsystem"</code>.</dd><dt>capsType</dt><dd>Options for the <code>type</code> attribute of the <hostdev/>
element in case of <code>mode="capabilities"</code>.</dd><dt>pciBackend</dt><dd>Options for the <code>name</code> attribute of the <driver/>
element.</dd></dl>
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