[pulseaudio-discuss] [PATCH v2] alsa: Check return value of snd_pcm_mmap_commit()

[Peter Meerwald]

From: Peter Meerwald <p.meerwald at bct-electronic.com>

snd_pcm_mmap_commit() actually transfers the memory area prepared by snd_pcm_mmap_begin(),
it returns the 'count of transferred frames' which should be equal to the number of frames
returned by snd_pcm_mmap_begin()

however, this identify is not checked and the number of frames prepared are accounted for,
not the number of frames commited -- this is wrong; the ALSA example codes bothers to
check snd_pcm_mmap_commit()'s returned number of frames

this patch just outputs a warning when sframes != frames -- let's see if it ever happens

v2: (thanks David Henningson)
* just log, no functional change as in v1
* fix typos, fix subject

Signed-off-by: Peter Meerwald <pmeerw at pmeerw.net>
---
 src/modules/alsa/alsa-sink.c   |   11 +++++++++--
 src/modules/alsa/alsa-source.c |   17 +++++++++++++----
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/modules/alsa/alsa-sink.c b/src/modules/alsa/alsa-sink.c
index e256bbd..35f013c 100644
--- a/src/modules/alsa/alsa-sink.c
+++ b/src/modules/alsa/alsa-sink.c
@@ -639,8 +639,7 @@ static int mmap_write(struct userdata *u, pa_usec_t *sleep_usec, bool polled, bo
 
             p = (uint8_t*) areas[0].addr + (offset * u->frame_size);
 
-            written = frames * u->frame_size;
-            chunk.memblock = pa_memblock_new_fixed(u->core->mempool, p, written, true);
+            chunk.memblock = pa_memblock_new_fixed(u->core->mempool, p, frames * u->frame_size, true);
             chunk.length = pa_memblock_get_length(chunk.memblock);
             chunk.index = 0;
 
@@ -660,6 +659,14 @@ static int mmap_write(struct userdata *u, pa_usec_t *sleep_usec, bool polled, bo
 
             work_done = true;
 
+            if (PA_UNLIKELY((snd_pcm_uframes_t) sframes != frames)) {
+                PA_ONCE_BEGIN {
+                    pa_log_warn("ALSA mmap write was set up for %lu frames, but unexpectedly commited %lu frames.\n",
+                        (unsigned long) frames, (unsigned long) sframes);
+                } PA_ONCE_END;
+            }
+
+            written = frames * u->frame_size;
             u->write_count += written;
             u->since_start += written;
 
diff --git a/src/modules/alsa/alsa-source.c b/src/modules/alsa/alsa-source.c
index 111c517..97d0d22 100644
--- a/src/modules/alsa/alsa-source.c
+++ b/src/modules/alsa/alsa-source.c
@@ -562,6 +562,7 @@ static int mmap_read(struct userdata *u, pa_usec_t *sleep_usec, bool polled, boo
             const snd_pcm_channel_area_t *areas;
             snd_pcm_uframes_t offset, frames;
             snd_pcm_sframes_t sframes;
+            size_t got;
 
             frames = (snd_pcm_uframes_t) (n_bytes / u->frame_size);
 /*             pa_log_debug("%lu frames to read", (unsigned long) frames); */
@@ -613,16 +614,24 @@ static int mmap_read(struct userdata *u, pa_usec_t *sleep_usec, bool polled, boo
 
             work_done = true;
 
-            u->read_count += frames * u->frame_size;
+            if (PA_UNLIKELY((snd_pcm_uframes_t) sframes != frames)) {
+                PA_ONCE_BEGIN {
+                    pa_log_warn("ALSA mmap read was set up for %lu frames, but unexpectedly commited %lu frames.\n",
+                        (unsigned long) frames, (unsigned long) sframes);
+                } PA_ONCE_END;
+            }
+
+            got = frames * u->frame_size;
+            u->read_count += got;
 
 #ifdef DEBUG_TIMING
-            pa_log_debug("Read %lu bytes (of possible %lu bytes)", (unsigned long) (frames * u->frame_size), (unsigned long) n_bytes);
+            pa_log_debug("Read %lu bytes (of possible %lu bytes)", (unsigned long) got, (unsigned long) n_bytes);
 #endif
 
-            if ((size_t) frames * u->frame_size >= n_bytes)
+            if (got >= n_bytes)
                 break;
 
-            n_bytes -= (size_t) frames * u->frame_size;
+            n_bytes -= got;
         }
     }
 
-- 
1.7.9.5