[libvirt] [PATCH 3/6] qemu: explicitly disable audio if there is no sound device

[Pavel Hrdina]

On Tue, Nov 21, 2017 at 12:09:54PM +0000, Daniel P. Berrange wrote:
> On Tue, Nov 21, 2017 at 01:02:05PM +0100, Peter Krempa wrote:
> > On Tue, Nov 21, 2017 at 11:48:20 +0000, Daniel Berrange wrote:
> > > On Tue, Nov 21, 2017 at 12:44:44PM +0100, Peter Krempa wrote:
> > > > On Tue, Nov 21, 2017 at 11:24:06 +0000, Daniel Berrange wrote:
> > > > > IOW, I don't think this patch is desirable.
> > > > 
> > > > We could allow hotplug only if qemu will allow to specify the sound
> > > > output per-soundcard which would avoid this problem.
> > > 
> > > I agree that having ability to configure distinct outputs per sound card
> > > might be useful, I don't think it is a blocking feature for hotplugging
> > > sound cards. ie, there's no reason why a user should not be able to
> > > unplug their current sound card, and plug in a new sound card for a
> > > running guests - they would only ever have 1 sound card present at
> > > a time in that scenario, so distinct outputs is not a requirement
> > > for that usecase.
> > 
> > While not a requirement, mandating that new features are available only
> > with new software sometimes saves a lot of headaches. I would not
> > mind if sound device hotplug will be supported only when specific
> > outputs can be selected when adding the sound card and would not work
> > without that.
> > 
> > Unfortunately qemu does not yet support this and I don't think that they
> > will any soon.
> 
> Agreed, and the most interesting thing for multiple audio cards is
> probably multi-seat support, which wouldn't need choosing between
> different backends, instead choosing different spice/vnc instances.
> 
> Basically, I think this patch should be dropped.

Ok, I don't mind dropping this patch.  At least it pointed out that
QEMU is design is broken.  This patch only affects use case where
the domain is started without any sound device and I personally don't
care if the audio output will be basically random unless you have
spice graphic configured.

However, if we enabled hot-plugging sound device we need to make sure
that we don't allow configuring sound output until we have a decent way
how to configure it.

Pavel
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