Re: [Qemu-devel] [PATCH v2 6/6] audio: -audiodev command line option

[Kővágó Zoltán]

2015-06-17 10:13 keltezéssel, Markus Armbruster írta:
> "Kővágó, Zoltán" <address@hidden> writes:
>
> > This patch adds an -audiodev command line option, and deprecates the QEMU_*
> > environment variables for audio backend configuration. It's syntax is similar to
> > existing options (-netdev, -device, etc):
> >   -audiodev driver_name,property=value,...
>
> Sounds really good.
>
> Please wrap your commit message lines a bit earlier, around column 70.
>
> > Audio drivers now get an Audiodev * as config paramters, instead of the global
> > audio_option structs. There is some code in audio/audio_legacy.c that converts
> > the old environment variables to audiodev options (this way backends do not have
> > to worry about legacy options, also print out them with -audio-help, to ease
> > migrating to -audiodev).
>
> The parenthesis isn't as clear as the rest of your message, probably
> because it deals with two separate things.  Suggest to move out the bit
> about help into its own paragraph.
>
> > Although now it's possible to specify multiple -audiodev options on command
> > line, multiple audio backends are not supported yet.
>
> What happens when I specify multiple -audiodev?

You get an error and qemu terminates.

> How should the command line look like when multiple audio backends are
> supported?

There's an id property of audiodev, so you can identify them:
-audiodev alsa,id=foo,... -audiodev pa,id=bar,...
and audio devices should get an extra parameter, like audiodev or 
something like that:
-device usb-audio,audiodev=foo -device usb-audio,audiodev=bar
And you have two cards, one connected to the alsa device and the other 
connected to pulseaudio.

> Do we have a clear backward-compatible path from here to there?

Currently if you specify an -audiodev option, the environment variables 
are completely ignored, and it will create an audio backend using the 
specified options. If you do not provide an -audiodev, it will 
initialize the audio subsystem using the old environment variables when 
you add the first sound card (so no -audiodev and no sound device means 
no audio subsystem, just like the old times).

About multiple backends: if the user does not specify the id of the 
backend when creating the sound card, just use the first -audiodev 
specified on the command line (or the legacy config, if there's no 
-audiodev). This way we stay backward-compatible (there won't be 
multiple -audiodevs in legacy configs).

> [...]
> >   18 files changed, 994 insertions(+), 1083 deletions(-)
> >   create mode 100644 audio/audio_legacy.c
>
> Very nice delta, but the size is a bit intimidating :)
>
> [...]