[alsa-devel] [PATCH] PulseAudio plugin: report XRUN state back to application

[Takashi Iwai]

At Sun, 25 Nov 2007 22:12:26 +0100,
Lennart Poettering wrote:
> 
> Hi!
> 
> Please consider merging this patch we ship in Fedora:
> 
> http://cvs.fedoraproject.org/viewcvs/*checkout*/devel/alsa-plugins/1.0.14-state-xrun.patch?rev=1.1
> 
> It adds support to report back XRUN to the application if one
> happens. This is required to make some applications work on top of the
> pulse plugin. One being XMMS, which checks if a song finished to play
> by waiting for an XRUN (yes, I don't argue that XMMS shouldn't do
> that, but nonetheless it is a good thing if XRUNs are reported
> properly.)
> 
> Now, this patch is a bit problematic, since it touches pcm->io.state
> which is not supposed to be touched by ioplug-based plugins --
> according to the comments in ioplug. However, I saw no other way to
> fix this, and from judging the ioplug code overwriting the variable
> should be safe. Thus I decided to simply touch the variable but
> documented it in a comment.
> 
> Alternatively, ioplug could be beefed up to properly handle XRUNs, but
> I thought this fix is simpler.

But it's a layer violation :)

We need a proper state-notification function.  It'd be simply setting
the state in the end, but at least, it's clear and the ioplug can do
any action or sanity-check if once needed.

A proposed patch is below.  Comments?


Takashi


diff -r 672c5387645d include/pcm_ioplug.h
--- a/include/pcm_ioplug.h	Fri Nov 23 15:46:48 2007 +0100
+++ b/include/pcm_ioplug.h	Mon Nov 26 11:32:10 2007 +0100
@@ -208,6 +208,9 @@ int snd_pcm_ioplug_set_param_minmax(snd_
 int snd_pcm_ioplug_set_param_minmax(snd_pcm_ioplug_t *io, int type, unsigned int min, unsigned int max);
 int snd_pcm_ioplug_set_param_list(snd_pcm_ioplug_t *io, int type, unsigned int num_list, const unsigned int *list);
 
+/* change PCM status */
+int snd_pcm_ioplug_set_state(snd_pcm_ioplug_t *ioplug, snd_pcm_state_t state);
+
 /** \} */
 
 #endif /* __ALSA_PCM_IOPLUG_H */
diff -r 672c5387645d src/pcm/pcm_ioplug.c
--- a/src/pcm/pcm_ioplug.c	Fri Nov 23 15:46:48 2007 +0100
+++ b/src/pcm/pcm_ioplug.c	Mon Nov 26 11:32:10 2007 +0100
@@ -614,6 +614,8 @@ static snd_pcm_sframes_t snd_pcm_ioplug_
 	snd_pcm_uframes_t avail;
 
 	snd_pcm_ioplug_hw_ptr_update(pcm);
+	if (io->data->state == SNDRV_PCM_STATE_XRUN)
+		return -EPIPE;
 	if (pcm->stream == SND_PCM_STREAM_CAPTURE &&
 	    pcm->access != SND_PCM_ACCESS_RW_INTERLEAVED &&
 	    pcm->access != SND_PCM_ACCESS_RW_NONINTERLEAVED) {
@@ -1037,3 +1039,19 @@ const snd_pcm_channel_area_t *snd_pcm_io
 		return snd_pcm_mmap_areas(ioplug->pcm);
 	return NULL;
 }
+
+/**
+ * \brief Change the ioplug PCM status
+ * \param ioplug the ioplug handle
+ * \param state the PCM status
+ * \return zero if successful or a negative error code
+ *
+ * Changes the PCM status of the ioplug to the given value.
+ * This function can be used for external plugins to notify the status
+ * change, e.g. XRUN.
+ */
+int snd_pcm_ioplug_set_state(snd_pcm_ioplug_t *ioplug, snd_pcm_state_t state)
+{
+	ioplug->state = state;
+	return 0;
+}