[alsa-devel] How to report error in _pointer function?

Takashi Iwai tiwai at suse.de
Mon Aug 11 09:19:20 CEST 2008

At Fri, 08 Aug 2008 17:26:11 -0500,
Timur Tabi wrote:
> Takashi Iwai wrote:
> > So, the PCM status is properly changed to XRUN as expected.  From the
> > driver perspective, everything must be fine.
> I've been debugging aplay.  The main loop is function pcm_write().  It calls
> writei_func() which returns -EPIPE.  This causes aplay to jump to xrun(), which
> attempts to recover.
> This is not what I want.  I don't want to return overrun/underrun.  I want to
> return failure.  Returning XRUN is wrong.
> Instead, I need to take a look at this code I have:
> 	snd_pcm_stream_lock_irqsave(substream, flags);
> 	if (snd_pcm_running(substream))
> 		snd_pcm_stop(substream, SNDRV_PCM_STATE_XRUN);
> 	snd_pcm_stream_unlock_irqrestore(substream, flags);
> It's the call to snd_pcm_stop() that I don't like.  There doesn't appear to be a
> SNDRV_PCM_STATE_xxx state that makes sense.  This function should eventually
> bring me to snd_pcm_pre_stop().  But this function returns -EBADFD because the
> current state is RUNNING and not OPEN.  Because it returns an error,
> snd_pcm_do_stop() is never called.

Hm?  snd_pcm_pre_stop() returns -EBADFD if the stream *IS* OPEN.
If it's RUNNING, it will stop the stream and change the state.

> This doesn't make any sense to me.  Why should I be able to stop a stream only
> if it's open but not running?  If it's open, but not running, then there's
> nothing to stop!  Can you explain the restriction in snd_pcm_pre_stop()?

If the state is OPEN, it means that the stream is already stopped.

Not sure which version you are referring, but I see no problem in the current code, at least...


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