Re: guest / host buffer sharing ...

[Stefan Hajnoczi]

On Fri, Nov 8, 2019 at 8:22 AM Gerd Hoffmann <address@hidden> wrote:
> > > Adding a list of common properties to the spec certainly makes sense,
> > > so everybody uses the same names.  Adding struct-ed properties for
> > > common use cases might be useful too.
> >
> > Why not define VIRTIO devices for wayland and friends?
>
> There is an out-of-tree implementation of that, so yes, that surely is
> an option.
>
> Wayland needs (a) shared buffers, mostly for gfx data, and (b) a stream
> pipe as control channel.  Pretty much the same for X11, except that
> shared buffers are optional because the X protocol can also squeeze all
> display updates through the stream pipe.
>
> So, if you want allow guests talk to the host display server you can run
> the stream pipe over vsock.  But there is nothing for the shared
> buffers ...
>
> We could replicate vsock functionality elsewhere.  I think that happened
> in the out-of-tree virtio-wayland implementation.  There also was some
> discussion about adding streams to virtio-gpu, slightly pimped up so you
> can easily pass around virtio-gpu resource references for buffer
> sharing.  But given that getting vsock right isn't exactly trivial
> (consider all the fairness issues when multiplexing multiple streams
> over a virtqueue for example) I don't think this is a good plan.

I also think vsock isn't the right fit.

Defining a virtio-wayland device makes sense to me: you get the guest
RAM access via virtqueues, plus the VIRTIO infrastructure (device IDs,
configuration space, feature bits, and existing reusable
kernel/userspace/QEMU code).

Stefan