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.. SPDX-License-Identifier: BSD-3-Clause
Copyright(c) 2010-2017 Intel Corporation.
Vhost_blk Sample Application
=============================
The vhost_blk sample application implemented a simple block device,
which used as the backend of Qemu vhost-user-blk device. Users can extend
the exist example to use other type of block device(e.g. AIO) besides
memory based block device. Similar with vhost-user-net device, the sample
application used domain socket to communicate with Qemu, and the virtio
ring (split or packed format) was processed by vhost_blk sample application.
The sample application reuse lots codes from SPDK(Storage Performance
Development Kit, https://github.com/spdk/spdk) vhost-user-blk target,
for DPDK vhost library used in storage area, user can take SPDK as
reference as well.
Testing steps
-------------
This section shows the steps how to start a VM with the block device as
fast data path for critical application.
Compiling the Application
-------------------------
To compile the sample application see :doc:`compiling`.
The application is located in the ``examples`` sub-directory.
You will also need to build DPDK both on the host and inside the guest
Start the vhost_blk example
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. code-block:: console
./dpdk-vhost_blk -m 1024
.. _vhost_blk_app_run_vm:
Start the VM
~~~~~~~~~~~~
.. code-block:: console
qemu-system-x86_64 -machine accel=kvm \
-m $mem -object memory-backend-file,id=mem,size=$mem,\
mem-path=/dev/hugepages,share=on -numa node,memdev=mem \
-drive file=os.img,if=none,id=disk \
-device ide-hd,drive=disk,bootindex=0 \
-chardev socket,id=char0,reconnect=1,path=/tmp/vhost.socket \
-device vhost-user-blk-pci,packed=on,chardev=char0,num-queues=1 \
...
.. note::
You must check whether your Qemu can support "vhost-user-blk" or not,
Qemu v4.0 or newer version is required.
reconnect=1 means live recovery support that qemu can reconnect vhost_blk
after we restart vhost_blk example.
packed=on means the device support packed ring but need the guest kernel
version >= 5.0.
Now Qemu commit 9bb73502321d46f4d320fa17aa38201445783fc4 both support the
vhost-blk reconnect and packed ring.
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