pcm_plugin: Fix return value of snd_pcm_rewind

In case the rewind did not rewind as much as expected, e g due to
time delay between the latest avail update and the rewind, we must
properly account for that in the plugin layer.

Otherwise, the plugin's appl ptr and the hw's appl ptr become
unsynchronised, which is very bad, especially in mmap_shadow plugins,
e g, this could cause the overlapping memcpy in the softvol plugin
as seen here:
https://bugs.freedesktop.org/show_bug.cgi?id=64299

Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>

diff --git a/src/pcm/pcm_plugin.c b/src/pcm/pcm_plugin.c
index 96218a8..17157e8 100644 (file)
--- a/src/pcm/pcm_plugin.c
+++ b/src/pcm/pcm_plugin.c
@@ -219,9 +219,9 @@ static snd_pcm_sframes_t snd_pcm_plugin_rewind(snd_pcm_t *pcm, snd_pcm_uframes_t
                snd_atomic_write_end(&plugin->watom);
                return sframes;
        }
-       snd_pcm_mmap_appl_backward(pcm, (snd_pcm_uframes_t) frames);
+       snd_pcm_mmap_appl_backward(pcm, (snd_pcm_uframes_t) sframes);
        snd_atomic_write_end(&plugin->watom);
-       return (snd_pcm_sframes_t) frames;
+       return (snd_pcm_sframes_t) sframes;
 }
 
 static snd_pcm_sframes_t snd_pcm_plugin_forwardable(snd_pcm_t *pcm)