sound: pcm: record a substream's owner process

Record the pid of the task that opened a PCM substream. For sound
cards with hardware mixing, this allows determining which process
is associated with a specific substream's volume control.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/sound/pcm.h

@@ -348,6 +348,8 @@ struct snd_pcm_group {		/* keep linked substreams */
 	int count;
 };
 
+struct pid;
+
 struct snd_pcm_substream {
 	struct snd_pcm *pcm;
 	struct snd_pcm_str *pstr;
@@ -379,6 +381,7 @@ struct snd_pcm_substream {
 	atomic_t mmap_count;
 	unsigned int f_flags;
 	void (*pcm_release)(struct snd_pcm_substream *);
+	struct pid *pid;
 #if defined(CONFIG_SND_PCM_OSS) || defined(CONFIG_SND_PCM_OSS_MODULE)
 	/* -- OSS things -- */
 	struct snd_pcm_oss_substream oss;

sound/core/pcm.c

@@ -435,6 +435,7 @@ static void snd_pcm_substream_proc_status_read(struct snd_info_entry *entry,
 		return;
 	}
 	snd_iprintf(buffer, "state: %s\n", snd_pcm_state_name(status.state));
+	snd_iprintf(buffer, "owner_pid   : %d\n", pid_vnr(substream->pid));
 	snd_iprintf(buffer, "trigger_time: %ld.%09ld\n",
 		status.trigger_tstamp.tv_sec, status.trigger_tstamp.tv_nsec);
 	snd_iprintf(buffer, "tstamp      : %ld.%09ld\n",
@@ -900,6 +901,7 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream,
 	substream->private_data = pcm->private_data;
 	substream->ref_count = 1;
 	substream->f_flags = file->f_flags;
+	substream->pid = get_pid(task_pid(current));
 	pstr->substream_opened++;
 	*rsubstream = substream;
 	return 0;
@@ -921,6 +923,8 @@ void snd_pcm_detach_substream(struct snd_pcm_substream *substream)
 	kfree(runtime->hw_constraints.rules);
 	kfree(runtime);
 	substream->runtime = NULL;
+	put_pid(substream->pid);
+	substream->pid = NULL;
 	substream->pstr->substream_opened--;
 }