ALSA: pcm - Fix drain behavior in non-blocking mode

The current PCM core has the following problems regarding PCM draining
in non-blocking mode:

- the current f_flags isn't checked in snd_pcm_drain(), thus changing
  the mode dynamically via snd_pcm_nonblock() after open doesn't work.
- calling drain in non-blocking mode just return -EAGAIN error, but
  doesn't provide any way to sync with draining.

This patch fixes these issues.
- check file->f_flags in snd_pcm_drain() properly
- when O_NONBLOCK is set, PCM core sets the stream(s) to DRAIN state
  but quits ioctl immediately without waiting the whole drain; the
  caller can sync the drain manually via poll()
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -197,13 +197,17 @@ static int snd_pcm_update_hw_ptr_post(struct snd_pcm_substream *substream,
 		avail = snd_pcm_capture_avail(runtime);
 	if (avail > runtime->avail_max)
 		runtime->avail_max = avail;
-	if (avail >= runtime->stop_threshold) {
-		if (substream->runtime->status->state == SNDRV_PCM_STATE_DRAINING)
+	if (runtime->status->state == SNDRV_PCM_STATE_DRAINING) {
+		if (avail >= runtime->buffer_size) {
 			snd_pcm_drain_done(substream);
-		else
+			return -EPIPE;
+		}
+	} else {
+		if (avail >= runtime->stop_threshold) {
 			xrun(substream);
 			return -EPIPE;
 		}
+	}
 	if (avail >= runtime->control->avail_min)
 		wake_up(&runtime->sleep);
 	return 0;

sound/core/pcm_native.c

@@ -1343,8 +1343,6 @@ static int snd_pcm_prepare(struct snd_pcm_substream *substream,
 
 static int snd_pcm_pre_drain_init(struct snd_pcm_substream *substream, int state)
 {
-	if (substream->f_flags & O_NONBLOCK)
-		return -EAGAIN;
 	substream->runtime->trigger_master = substream;
 	return 0;
 }
@@ -1392,7 +1390,6 @@ static struct action_ops snd_pcm_action_drain_init = {
 struct drain_rec {
 	struct snd_pcm_substream *substream;
 	wait_queue_t wait;
-	snd_pcm_uframes_t stop_threshold;
 };
 
 static int snd_pcm_drop(struct snd_pcm_substream *substream);
@@ -1404,13 +1401,15 @@ static int snd_pcm_drop(struct snd_pcm_substream *substream);
  * After this call, all streams are supposed to be either SETUP or DRAINING
  * (capture only) state.
  */
-static int snd_pcm_drain(struct snd_pcm_substream *substream)
+static int snd_pcm_drain(struct snd_pcm_substream *substream,
+			 struct file *file)
 {
 	struct snd_card *card;
 	struct snd_pcm_runtime *runtime;
 	struct snd_pcm_substream *s;
 	int result = 0;
 	int i, num_drecs;
+	int nonblock = 0;
 	struct drain_rec *drec, drec_tmp, *d;
 
 	card = substream->pcm->card;
@@ -1428,6 +1427,15 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream)
 		}
 	}
 
+	if (file) {
+		if (file->f_flags & O_NONBLOCK)
+			nonblock = 1;
+	} else if (substream->f_flags & O_NONBLOCK)
+		nonblock = 1;
+
+	if (nonblock)
+		goto lock; /* no need to allocate waitqueues */
+
 	/* allocate temporary record for drain sync */
 	down_read(&snd_pcm_link_rwsem);
 	if (snd_pcm_stream_linked(substream)) {
@@ -1449,16 +1457,11 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream)
 			d->substream = s;
 			init_waitqueue_entry(&d->wait, current);
 			add_wait_queue(&runtime->sleep, &d->wait);
-			/* stop_threshold fixup to avoid endless loop when
-			 * stop_threshold > buffer_size
-			 */
-			d->stop_threshold = runtime->stop_threshold;
-			if (runtime->stop_threshold > runtime->buffer_size)
-				runtime->stop_threshold = runtime->buffer_size;
 		}
 	}
 	up_read(&snd_pcm_link_rwsem);
 
+ lock:
 	snd_pcm_stream_lock_irq(substream);
 	/* resume pause */
 	if (substream->runtime->status->state == SNDRV_PCM_STATE_PAUSED)
@@ -1466,9 +1469,12 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream)
 
 	/* pre-start/stop - all running streams are changed to DRAINING state */
 	result = snd_pcm_action(&snd_pcm_action_drain_init, substream, 0);
-	if (result < 0) {
-		snd_pcm_stream_unlock_irq(substream);
-		goto _error;
+	if (result < 0)
+		goto unlock;
+	/* in non-blocking, we don't wait in ioctl but let caller poll */
+	if (nonblock) {
+		result = -EAGAIN;
+		goto unlock;
 	}
 
 	for (;;) {
@@ -1504,18 +1510,18 @@ static int snd_pcm_drain(struct snd_pcm_substream *substream)
 		}
 	}
 
+ unlock:
 	snd_pcm_stream_unlock_irq(substream);
 
- _error:
+	if (!nonblock) {
 		for (i = 0; i < num_drecs; i++) {
 			d = &drec[i];
 			runtime = d->substream->runtime;
 			remove_wait_queue(&runtime->sleep, &d->wait);
-		runtime->stop_threshold = d->stop_threshold;
 		}
-
 		if (drec != &drec_tmp)
 			kfree(drec);
+	}
 	snd_power_unlock(card);
 
 	return result;
@@ -2544,7 +2550,7 @@ static int snd_pcm_common_ioctl1(struct file *file,
 		return snd_pcm_hw_params_old_user(substream, arg);
 #endif
 	case SNDRV_PCM_IOCTL_DRAIN:
-		return snd_pcm_drain(substream);
+		return snd_pcm_drain(substream, file);
 	case SNDRV_PCM_IOCTL_DROP:
 		return snd_pcm_drop(substream);
 	case SNDRV_PCM_IOCTL_PAUSE: