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Re: Fwd: VirtioSound device emulation implementation

From: Shreyansh Chouhan
Subject: Re: Fwd: VirtioSound device emulation implementation
Date: Thu, 28 Jan 2021 21:20:31 +0530

(Gerd, I wasn't able to get gmail to quote your email, so I have just copy pasted the relavant parts.)

> Yes.  net_conf is common config (backend, mac address, maybe more) for
> network devices.  For sound devices that would audiodev (link the device
> to a backend which then handles alsa/pulse/jack/oss/sdl/whatever).

Ah I see, so the net_conf corresponds to audiodev? I thought it would correspond
to `virtio_snd_conf`. So as alex said, `virtio_snd_conf` is the front end configuration.

> Configuration can be done either using device properties, or by having
> different devices.  Using device properties is probably the easier way
> to go.  An example for the latter are the qemu hda codecs.  We have
> three different devices:

>  (1) hda-output: playback-only, offering a virtual line-out.
>  (2) hda-duplex: record/playback, offering line-in and line-out.
>  (3) hda-micro:  record/playback, offering microphone and speaker.

> The difference between (2) and (3) is just the jack labeling, otherwise
> the behavior is 100% identical (and they share the emulation code of
> course).  But some windows VoIP apps didn't like the line-in and
> complained about a missing microphone, so we added that ...

>> The thing is I do not understand `net` devices all that well so I get a bit
>> confused with
>> what is specific to a net device and what should I actually be worried
>> about :)

> The only thing really required is the audiodev property.  Everything
> else can be hard-coded initially, and once the basics are working
> refined (like adding properties for jack labels, ...).

So in the realize function I set up the audiodev, right? Also in that case
why the difference between the net and sound devices? In the net
device we set up the common config in net_conf. Does the net_conf
somehow later sets up NetDev too?

And what is a NetClientState? Is the NetClient the emulated guest? This
confuses me a lot. I can't understand what will be the parellel audio device

Also I can't seem to find where we parse the command line options passed to qemu.
The code structure is a bit different from what I had expected. In virtio_net_device_realize
we set duplex to half or full depending on the value of the net_conf.duplex_str. But I
couldn't find where we actually set it.

cc Alex


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