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

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] revising virtio-vhost-user device
Date: Thu, 18 Apr 2019 10:52:44 +0100
User-agent: Mutt/1.11.3 (2019-02-01)

On Wed, Apr 17, 2019 at 05:05:31PM +0300, Nikos Dragazis wrote:
> 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.

Hi Nikos,
Nice to see your progress on this feature!

Please send the VIRTIO specification changes to
address@hidden  For more info, see

Getting the specification approved is important so that QEMU can merge
the device implementation.  SPDK may be willing to merge code before it
is an official VIRTIO spec, but this will lead to problems with
non-compliant implementations and confusion for users when devices don't
work due to version mismatches.  I suggest focussing on getting
agreement on the spec.

Guidelines for submitting QEMU patches are here:

Please CC me on the VIRTIO and QEMU patches.  I'll be happy to review

Note that David Gilbert has posted a shared memory resources patch for
the VIRTIO specification.  virtio-vhost-vsock should use this mechanism:


> 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

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