Re: Fwd: VirtioSound device emulation implementation

[Shreyansh Chouhan <chouhan.shreyansh2702@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2793 bytes --]

On Thu, 14 Jan 2021 at 23:17, Alex Bennée <alex.bennee@linaro.org> wrote:

>
> Shreyansh Chouhan <chouhan.shreyansh2702@gmail.com> writes:
>
> > Just an update:
> >
> > I've studied the virtio specification along with the source code and I
> now
> > understand what the device implementation is
> > going to look like. Also I understand the source code a lot better. I am
> > now reading about the qemu vhost-user protocol.
> >
> > Although I haven't read about the vhost-user daemon in detail, from what
> > little I have read, I would say that the daemon
> > would get the virtqueues from the virtio device and forward it to the
> sound
> > device of the host. (This is the hard part
> > I think, since an in QEMU device would use code already written for
> > processing these queues.)
>
> I can't comment on the difficulty there but this does point more towards
> using the in-QEMU approach given we have a bunch of utility functions
> already.
>
> > I think only the tx and rx
> > queues would be shared, and although I do not know exactly how the
> sharing
> > will be implemented, I think the memory
> > will be shared to the vhost-user daemon too? So now the virtqueue memory
> is
> > shared between the virtio driver in guest
> > OS, the virtio device in QEMU, and the vhost-user daemon running in the
> > host userspace.
>
> QEMU uses a memfd file descriptor to share the guests entire memory map
> with the daemon.
>
Oh I see.

>
> > As for the configuration part, the driver will negotiate features with
> the
> > virtio device in QEMU, which in turn will communicate
> > with the vhost-user daemon (via sockets) to get the features supported I
> > think.
> >
> > This is what I think it will roughly look like. (Of course modulo the
> > implementation details.) I do not yet understand how
> > much more difficult will implementing the vhost-user daemon be, and
> since I
> > was already
> > warned about the difficulty, I will not risk making any hasty decisions
> > that later hinder the project. I will read up
> > about the vhost-user daemon and how it's implemented to get a better
> idea,
> > and then make the final call.
>
> If you want to see an example of a branch new vhost-user daemon being
> built up from scratch see my recent virtio-rpmb series. The first few
> patches of in-QEMU code will be the same boilerplate either way I think:
>
>   https://patchew.org/QEMU/20200925125147.26943-1-alex.bennee@linaro.org/

This looks super helpful! Thanks a lot for this.

>
>
> > Anyways I am super excited about the project. I got to learn about some
> > really cool things in the past couple of days,
> > and I can not wait to implement it. :)
>
>
> --
> Alex Bennée
>


- Shreyansh Chouhan

[-- Attachment #2: Type: text/html, Size: 3841 bytes --]