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

Daniel P. Berrange berrange at redhat.com
Tue Nov 21 12:24:24 UTC 2017


On Tue, Nov 21, 2017 at 01:21:26PM +0100, Pavel Hrdina wrote:
> 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.

Agreed - that's pretty much why i never exposed sound backend in the XML
and instead hardcoded it with optional override in qemu.conf when first
doing this

Regards,
Daniel
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