Re: [virtio-dev] Request for a new device number for a virtio-audio device.

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Mon, Apr 29, 2019 at 07:39:17PM +0200, Marco Martinelli - 13Byte srl wrote:
> Il 29/04/19 15:47, Stefan Hajnoczi ha scritto:
> > On Mon, Apr 29, 2019 at 12:22:41AM +0200, Marco Martinelli - 13Byte srl wrote:
> > > I'm not sure how this works, is that number already assigned and I should
> > > use that or should I get a new one?
> > > 
> > > For last, I have a question to clear the things up for me. It is my
> > > understanding that in this mailing list you discuss about the
> > > specifications, not the actual code. What's the usual process when writing a
> > > new virtio device?
> > > Should I start with writing the code and then document how it works or is it
> > > the opposite? Should I document it and have it approved and then implement
> > > the specifications?
> > > 
> > > I know that this may sound like a stupid question, but please be patient
> > > with me, it's my first time.
> > I suggest posting a draft specification for the new device type before
> > investing too much time in the implementation.
> > 
> > Then work on the code while the spec discussion is ongoing.  This way
> > you won't have to wait too long before implementation but you also won't
> > find that reviewers are asking for large changes after you completed
> > your work.
> I feared that would be the answer.
> As I stated I'm not familiar with most of the technologies involved. I don't
> know if I have the capabilities to write a draft of the specifications
> without first working on some code to clear things up.
> I'll try my best.

I'm happy to help you get started.

I have a basic understanding of sound cards (mostly from an audio API
and application perspective) and can explain the virtio device model.

Please post the requirements and scope of the device you'd like to
create.  Are you thinking of something general-purpose like the USB
Audio Device Class specification, which can handle many different types
of devices.  Or were you thinking of something more limited?

In terms of virtio concepts, audio streams would be transferred in
chunks over virtqueues.  A "control" virtqueue might be necessary to
configure the device.  It would process configuration request/response
packets.

Stefan

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