ALSA: pcm: Workaround for weird PulseAudio behavior on rewind error (fb51f1cd) · Commits · 戴 / test

The commit ("ALSA: pcm: Call ack() whenever appl_ptr is updated") introduced the possible error code returned from the PCM rewind ioctl. Basically the change was for handling the indirect PCM more correctly, but ironically, it caused rather a side-effect: PulseAudio gets pissed off when receiving an error from rewind, throws everything away and stops processing further, resulting in the silence. It's clearly a failure in the application side, so the best would be to fix that bug in PA. OTOH, PA is mostly the only user of the rewind feature, so it's not good to slap the sole customer. This patch tries to mitigate the situation: instead of returning an error, now the rewind ioctl returns zero when the driver can't rewind. It indicates that no rewind was performed, so the behavior is consistent, at least. Fixes: ("ALSA: pcm: Call ack() whenever appl_ptr is updated") Cc: <stable@vger.kernel.org> Signed-off-by:

Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

+7 −2

Original line number	Original line	Diff line number	Diff line
	@@ -2580,7 +2580,7 @@ static snd_pcm_sframes_t forward_appl_ptr(struct snd_pcm_substream *substream,
	return ret < 0 ? ret : frames;		return ret < 0 ? ret : frames;
	}		}

	/* decrease the appl_ptr; returns the processed frames or a negative error */		/* decrease the appl_ptr; returns the processed frames or zero for error */
	static snd_pcm_sframes_t rewind_appl_ptr(struct snd_pcm_substream *substream,		static snd_pcm_sframes_t rewind_appl_ptr(struct snd_pcm_substream *substream,
	snd_pcm_uframes_t frames,		snd_pcm_uframes_t frames,
	snd_pcm_sframes_t avail)		snd_pcm_sframes_t avail)
	@@ -2597,7 +2597,12 @@ static snd_pcm_sframes_t rewind_appl_ptr(struct snd_pcm_substream *substream,
	if (appl_ptr < 0)		if (appl_ptr < 0)
	appl_ptr += runtime->boundary;		appl_ptr += runtime->boundary;
	ret = pcm_lib_apply_appl_ptr(substream, appl_ptr);		ret = pcm_lib_apply_appl_ptr(substream, appl_ptr);
	return ret < 0 ? ret : frames;		/* NOTE: we return zero for errors because PulseAudio gets depressed
			* upon receiving an error from rewind ioctl and stops processing
			* any longer. Returning zero means that no rewind is done, so
			* it's not absolutely wrong to answer like that.
			*/
			return ret < 0 ? 0 : frames;
	}		}

	static snd_pcm_sframes_t snd_pcm_playback_rewind(struct snd_pcm_substream *substream,		static snd_pcm_sframes_t snd_pcm_playback_rewind(struct snd_pcm_substream *substream,

Admin message