Re: [Qemu-devel] [PATCH 02/11] audio: basic support for multi backend audio

[Zoltán Kővágó]

On 2019-07-11 16:37, Markus Armbruster wrote:
> "Zoltán Kővágó" <address@hidden> writes:
> 
>> On 2019-07-10 06:06, Markus Armbruster wrote:
>>> "Kővágó, Zoltán" <address@hidden> writes:
>>>
>>>> Audio functions no longer access glob_audio_state, instead they get an
>>>> AudioState as a parameter.  This is required in order to support
>>>> multiple backends.
>>>>
>>>> glob_audio_state is also gone, and replaced with a tailq so we can store
>>>> more than one states.
>>>>
>>>> Signed-off-by: Kővágó, Zoltán <address@hidden>
>>>> ---
>>> [...]
>>>> diff --git a/hmp-commands.hx b/hmp-commands.hx
>>>> index bfa5681dd2..23196da3fe 100644
>>>> --- a/hmp-commands.hx
>>>> +++ b/hmp-commands.hx
>>>> @@ -819,16 +819,17 @@ ETEXI
>>>>  
>>>>      {
>>>>          .name       = "wavcapture",
>>>> -        .args_type  = "path:F,freq:i?,bits:i?,nchannels:i?",
>>>> -        .params     = "path [frequency [bits [channels]]]",
>>>> +        .args_type  = "path:F,freq:i?,bits:i?,nchannels:i?,audiodev:s?",
>>>> +        .params     = "path [frequency [bits [channels [audiodev]]]]",
>>>>          .help       = "capture audio to a wave file (default 
>>>> frequency=44100 bits=16 channels=2)",
>>>>          .cmd        = hmp_wavcapture,
>>>>      },
>>>>  STEXI
>>>> -@item wavcapture @var{filename} [@var{frequency} [@var{bits} 
>>>> [@var{channels}]]]
>>>> +@item wavcapture @var{filename} [@var{frequency} [@var{bits} 
>>>> [@var{channels} [@var{audiodev}]]]]
>>>>  @findex wavcapture
>>>> -Capture audio into @var{filename}. Using sample rate @var{frequency}
>>>> -bits per sample @var{bits} and number of channels @var{channels}.
>>>> +Capture audio into @var{filename} from @var{audiodev}. Using sample rate
>>>> +@var{frequency} bits per sample @var{bits} and number of channels
>>>> +@var{channels}.
>>>>  
>>>>  Defaults:
>>>>  @itemize @minus
>>>    @item Sample rate = 44100 Hz - CD quality
>>>    @item Bits = 16
>>>    @item Number of channels = 2 - Stereo
>>>    @end itemize
>>>    ETEXI
>>>
>>> Defaults for the other optional arguments are listed here.  Why not for
>>> @audiodev?
>>
>> There's no default listed because there's no default when you use the
>> -audiodev options, since there's no good default.  When you don't use
>> -audiodev, it'll use the implicitly created audiodev which doesn't have
>> a name, so it can't be specified.
> 
> Double-checking to avoid misunderstandings: there is a default
> *behavior*, but no default *value*, i.e. there is no VALUE that makes
> audiodev=VALUE give you the same behavior as no audiodev.  Correct?

Yes.  If there is no audiodev=VALUE, and no -audiodev on the command
line, use the legacy config.  If there is audiodev=VALUE and -audiodev
id=VALUE, use that device.  Otherwise, it's an error.

> 
>>                                    But I agree that this situation
>> should be documented somehow.
> 
> Yes, please.
> 
>>>> diff --git a/qemu-options.hx b/qemu-options.hx
>>>> index 9621e934c0..0111055aa4 100644
>>>> --- a/qemu-options.hx
>>>> +++ b/qemu-options.hx
>>>> @@ -1978,6 +1978,11 @@ can help the device and guest to keep up and not 
>>>> lose events in case
>>>>  events are arriving in bulk.  Possible causes for the latter are flaky
>>>>  network connections, or scripts for automated testing.
>>>>  
>>>> +@item audiodev=@var{audiodev}
>>>> +
>>>> +Use the specified @var{audiodev} when the VNC client requests audio
>>>> +transmission.
>>>> +
>>>
>>> What's the default?
>>
>> It's the same story as wav_capture.
>>
>> Regards,
>> Zoltan