[Qemu-devel] revising virtio-vhost-user device

[Nikos Dragazis]

Hi everyone,

as you may already know, there is an experimental feature in QEMU wiki
page called “virtio-vhost-user” [1]. Stefan Hajnoczi launched this
feature a year ago. He even wrote an RFC implementation [2]. However,
this feature is still a WIP.

At present, I am working with Dariusz Stojaczyk from Intel in order to
integrate the virtio-vhost-user device with SPDK/DPDK. Part of the plan
is to finish up and merge the virtio-vhost-user device with the latest
QEMU. Thereby, I have been working on Stefan’s device code [3] over the
last few weeks. Stefan has already made a TODO list [2] with all the
missing parts.

The updated device code is here [4]. In short, I have done the following
things so far:

- implement the virtio PCI capabilities for the additional device
  resources

- add support for guest notifications in response to master virtqueue
  kicks

- use ioeventfd mechanism for the callfds in order to avoid entering
  QEMU

- add UUID configuration field

- rebase on top of latest qemu:master

- update the virtio device spec [5][6]

I have deliberately kept the commits separate in order to clearly
demonstrate the above changes.

There is still some work to be done. However, given the fact that I am
not familiar with QEMU code and development process, I thought about
sharing this with the community at an early stage. Hopefully, I could
receive from you some reviews/pointers/comments/suggestions.

Looking forward to your feedback.

Best regards,
Nikos

[1] https://wiki.qemu.org/Features/VirtioVhostUser
[2] http://lists.nongnu.org/archive/html/qemu-devel/2018-01/msg04806.html
[3] https://github.com/stefanha/qemu/tree/virtio-vhost-user
[4] https://github.com/arrikto/qemu-qemu/commits/virtio-vhost-user
[5] https://github.com/ndragazis/virtio/commits
[6] https://ndragazis.github.io/virtio-v1.0-cs04.html#x1-2830007