Re: [Qemu-devel] [PATCH v2 4/4] audio: paaudio: ability to specify stream name

[Daniel P . Berrangé]

On Wed, Aug 28, 2019 at 12:43:49AM +0200, Zoltán Kővágó wrote:
> On 2019-08-27 07:42, Gerd Hoffmann wrote:
> > On Mon, Aug 26, 2019 at 09:59:04PM +0200, Kővágó, Zoltán wrote:
> >> This can be used to identify stream in tools like pavucontrol when one
> >> creates multiple -audiodevs or runs multiple qemu instances.
> > 
> > Hmm, can we create an useful name automatically, without yet another
> > config option?
> > 
> > Useful choices could be the device name (usb-audio, ...) or the device
> > id (whatever -device id=xxx was specified on the command line).
> 
> I'm afraid this is not going to work with the current architecture: due
> to mixeng even if you have multiple devices, they'll be mixed to a
> single stream and the audio backend will only see this one mixed stream.
>  As a workaround we could do something like concat all device names or
> ids, but I don't like that idea.
> 
> Alternatively we could use the id of the audiodev instead, and no more
> problems with mixeng.  However, with mixeng off (implemented in my next
> patch series) suddenly soundcards will have suddenly end up as different
> streams.  (This can be worked around by creating multiple audiodevs,
> like what you have to use now to get multiple streams from pa, so this
> is probably a smaller problem.)
> 
> Currently I'm leaning for the audiodev's id option, unless someone
> proposes something better.

Using the audiodev id is not a good idea. If you have multiple QEMU's
on your host, it is highly likely that libvirt will have assigned
the same audiodev id to all of them.  Using the vm name would be ok,
but only if you assume that each gust only has a single audio device.

Using a combination of vm name + audidev id is going to be unique
per host, but not especially friendly as a user visible name. It
would be ok as a default, but I'd think we should let the mgmt app
specify stream name explicitly, so that something user friendly
can be set.

Regards,
Daniel
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