Re: [PATCH 2/3] qapi, audio: respect build time conditions in audio schema

[Daniel P . Berrangé]

On Wed, Mar 03, 2021 at 08:00:59AM +0100, Gerd Hoffmann wrote:
> On Tue, Mar 02, 2021 at 05:55:23PM +0000, Daniel P. Berrangé wrote:
> > Currently the -audiodev accepts any audiodev type regardless of what is
> > built in to QEMU. An error only occurs later at runtime when a sound
> > device tries to use the audio backend.
> > 
> > With this change QEMU will immediately reject -audiodev args that are
> > not compiled into the binary. The QMP schema will also be introspectable
> > to identify what is compiled in.
> 
> Note that audio backends are modularized, so "compiled with
> CONFIG_AUDIO_ALSA" doesn't imply "alsa support is available".

AFAIK, there's no way to handle this with QAPI schema reporting. We
can only conditionalize based on what's available at compile time,
not what's installed at runtime.

To get runtime info, we would have to introduce an explicit
"query-audiodev-types" command where just report the backends
that have been installed.

Regards,
Daniel
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