[alsa-devel] multi pcm and mmap problem

[Takashi Iwai]

At Fri, 23 Nov 2007 14:41:43 +0100,
I wrote:
> 
> Try the patch below.  This should fix the problem.  Now the multi
> plugin just shadows the slave buffers via mmap.

There was a minor bug in the last patch.  The revised version is
below.


Takashi

diff -r 3539f279ec38 src/pcm/pcm_multi.c
--- a/src/pcm/pcm_multi.c	Wed Nov 21 12:19:43 2007 +0100
+++ b/src/pcm/pcm_multi.c	Fri Nov 23 15:34:16 2007 +0100
@@ -690,13 +690,44 @@ static snd_pcm_sframes_t snd_pcm_multi_m
 	return size;
 }
 
-static int snd_pcm_multi_mmap(snd_pcm_t *pcm ATTRIBUTE_UNUSED)
+static int snd_pcm_multi_munmap(snd_pcm_t *pcm)
 {
+	free(pcm->mmap_channels);
+	free(pcm->running_areas);
+	pcm->mmap_channels = NULL;
+	pcm->running_areas = NULL;
 	return 0;
 }
 
-static int snd_pcm_multi_munmap(snd_pcm_t *pcm ATTRIBUTE_UNUSED)
+static int snd_pcm_multi_mmap(snd_pcm_t *pcm)
 {
+	snd_pcm_multi_t *multi = pcm->private_data;
+	unsigned int c;
+
+	pcm->mmap_channels = calloc(pcm->channels,
+				    sizeof(pcm->mmap_channels[0]));
+	pcm->running_areas = calloc(pcm->channels,
+				    sizeof(pcm->running_areas[0]));
+	if (!pcm->mmap_channels || !pcm->running_areas) {
+		snd_pcm_multi_munmap(pcm);
+		return -ENOMEM;
+	}
+
+	/* Copy the slave mmapped buffer data */
+	for (c = 0; c < pcm->channels; c++) {
+		snd_pcm_multi_channel_t *chan = &multi->channels[c];
+		snd_pcm_t *slave;
+		if (chan->slave_idx < 0) {
+			snd_pcm_multi_munmap(pcm);
+			return -ENXIO;
+		}
+		slave = multi->slaves[chan->slave_idx].pcm;
+		pcm->mmap_channels[c] =
+			slave->mmap_channels[chan->slave_channel];
+		pcm->mmap_channels[c].channel = c;
+		pcm->running_areas[c] =
+			slave->running_areas[chan->slave_channel];
+	}
 	return 0;
 }
 
@@ -850,6 +881,7 @@ int snd_pcm_multi_open(snd_pcm_t **pcmp,
 		return err;
 	}
 	pcm->mmap_rw = 1;
+	pcm->mmap_shadow = 1; /* has own mmap method */
 	pcm->ops = &snd_pcm_multi_ops;
 	pcm->fast_ops = &snd_pcm_multi_fast_ops;
 	pcm->private_data = multi;