ALSA: pcm: Return 0 when size < start_threshold in capture

Commit Message

Ricardo Biehl Pasquali Aug. 21, 2018, 7:46 p.m. UTC

In __snd_pcm_lib_xfer(), when capture, if state is
PREPARED and size is less than start_threshold nothing
can be done. As there is no error, 0 is returned.

Am I missing something?

Cheers!

	pasquali

Comments

Takashi Iwai Aug. 22, 2018, 7:53 a.m. UTC | #1

On Tue, 21 Aug 2018 21:46:43 +0200,
Ricardo Biehl Pasquali wrote:
> 
> In __snd_pcm_lib_xfer(), when capture, if state is
> PREPARED and size is less than start_threshold nothing
> can be done. As there is no error, 0 is returned.
> 
> Am I missing something?

Not really :)
It's just an undefined behavior, so far, and yes, the suggested
behavior makes more sense.

Could you resubmit a proper patch for merging?  Please follow
Documentation/process/submitting-patches.rst.


thanks,

Takashi

Patch

--- pcm_lib.c.orig	2018-08-21 15:31:54.457405053 -0300
+++ pcm_lib.c	2018-08-21 15:56:01.264549084 -0300
@@ -2125,7 +2125,7 @@ 
 	pcm_transfer_f transfer;
 	bool nonblock;
 	bool is_playback;
-	int err;
+	int err = 0;
 
 	err = pcm_sanity_check(substream);
 	if (err < 0)
@@ -2173,11 +2173,15 @@ 
 		goto _end_unlock;
 
 	if (!is_playback &&
-	    runtime->status->state == SNDRV_PCM_STATE_PREPARED &&
-	    size >= runtime->start_threshold) {
-		err = snd_pcm_start(substream);
-		if (err < 0)
+	    runtime->status->state == SNDRV_PCM_STATE_PREPARED) {
+		if (size >= runtime->start_threshold) {
+			err = snd_pcm_start(substream);
+			if (err < 0)
+				goto _end_unlock;
+		} else {
+			/* nothing to do */
 			goto _end_unlock;
+		}
 	}
 
 	runtime->twake = runtime->control->avail_min ? : 1;