[ALSA] Add O_APPEND flag support to PCM

Added O_APPEND flag support to PCM to enable shared substreams
among multiple processes.  This mechanism is used by dmix and
dsnoop plugins.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 23 insertions, 2 deletions

diff --git a/sound/core/pcm.c b/sound/core/pcm.c
index 4f5204175d37..8136be2e6066 100644
--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -829,6 +829,26 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
                 return -EINVAL;
         }
 
+        if (file->f_flags & O_APPEND) {
+                if (prefer_subdevice < 0) {
+                        if (pstr->substream_count > 1)
+                                return -EINVAL; /* must be unique */
+                        substream = pstr->substream;
+                } else {
+                        for (substream = pstr->substream; substream;
+                             substream = substream->next)
+                                if (substream->number == prefer_subdevice)
+                                        break;
+                }
+                if (! substream)
+                        return -ENODEV;
+                if (! SUBSTREAM_BUSY(substream))
+                        return -EBADFD;
+                substream->ref_count++;
+                *rsubstream = substream;
+                return 0;
+        }
+
         if (prefer_subdevice >= 0) {
                 for (substream = pstr->substream; substream; substream = substream->next)
                         if (!SUBSTREAM_BUSY(substream) && substream->number == prefer_subdevice)
@@ -873,7 +893,8 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
 
         substream->runtime = runtime;
         substream->private_data = pcm->private_data;
-        substream->ffile = file;
+        substream->ref_count = 1;
+        substream->f_flags = file->f_flags;
         pstr->substream_opened++;
         *rsubstream = substream;
         return 0;
@@ -882,7 +903,7 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
 void snd_pcm_detach_substream(struct snd_pcm_substream *substream)
 {
         struct snd_pcm_runtime *runtime;
-        substream->file = NULL;
+
         runtime = substream->runtime;
         snd_assert(runtime != NULL, return);
         if (runtime->private_free != NULL)