pcm: Add PCM_NORESTART flag

Add a flag which can be passed to pcm_open (called PCM_NORESTART).
When set on a playback stream, calls to pcm_write will not
automatically attempt to restart an ALSA device in the case of an
underflow.  Instead, it will propagate the first EPIPE error up to the
application to allow it to handle the underflow situation.  Subsequent
calls to pcm_write will attempt to start the pipeline.

1 files changed, 5 insertions, 1 deletions

diff --git a/pcm.c b/pcm.c
index d253433..2dca157 100644
--- a/pcm.c
+++ b/pcm.c
@@ -378,8 +378,12 @@ int pcm_write(struct pcm *pcm, const void *data, unsigned int count)
         if (ioctl(pcm->fd, SNDRV_PCM_IOCTL_WRITEI_FRAMES, &x)) {
             pcm->running = 0;
             if (errno == EPIPE) {
-                    /* we failed to make our window -- try to restart */
+                /* we failed to make our window -- try to restart if we are
+                 * allowed to do so.  Otherwise, simply allow the EPIPE error to
+                 * propagate up to the app level */
                 pcm->underruns++;
+                if (pcm->flags & PCM_NORESTART)
+                    return -EPIPE;
                 continue;
             }
             return oops(pcm, errno, "cannot write stream data");