pcm: dmix: Workaround for binary incompatibility

The commit 1a9bd0f04481 ("pcm: direct: Fix for sync issue on xrun
recover") introduced a new field "recoveries" in
snd_pcm_direct_share_t.  Unfortunately this caused two issues:

- It changed the size of the struct which is used as the magic key
- The struct size differs between 32bit and 64bit due to alignment

The former brought the incompatibility with the older alsa-lib,
e.g. when you run an app with an older alsa-lib via LD_PRELOAD, it
doesn't work any longer.

The latter is more serious, it disallows running 32bit apps dmix with
64bit together.

As a workaround, put recoveries field to the unused field
"s.xfer_align", so that the struct is in an old form.  This makes the
dmix again binary-compatible with 1.1.3 and older versions, and also
fix the incompatibility between 32/64 bits.

This is a one-time workaround, and we may need to reconsider more
about a breakage in future...

Fixes: 1a9bd0f04481 ("pcm: direct: Fix for sync issue on xrun recover")
Reported-and-tested-by: Cheng Sun <chengsun9@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c
index 89468d3..4370260 100644 (file)
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -615,7 +615,7 @@ int snd_pcm_direct_slave_recover(snd_pcm_direct_t *direct)
                }
                return ret;
        }
-       direct->shmptr->recoveries++;
+       direct->shmptr->s.recoveries++;
        semerr = snd_pcm_direct_semaphore_up(direct,
                                                 DIRECT_IPC_SEM_CLIENT);
        if (semerr < 0) {
@@ -631,11 +631,11 @@ int snd_pcm_direct_slave_recover(snd_pcm_direct_t *direct)
  */
 int snd_pcm_direct_client_chk_xrun(snd_pcm_direct_t *direct, snd_pcm_t *pcm)
 {
-       if (direct->shmptr->recoveries != direct->recoveries) {
+       if (direct->shmptr->s.recoveries != direct->recoveries) {
                /* no matter how many xruns we missed -
                 * so don't increment but just update to actual counter
                 */
-               direct->recoveries = direct->shmptr->recoveries;
+               direct->recoveries = direct->shmptr->s.recoveries;
                pcm->fast_ops->drop(pcm);
                /* trigger_tstamp update is missing in drop callbacks */
                gettimestamp(&direct->trigger_tstamp, pcm->tstamp_type);
@@ -1539,7 +1539,7 @@ int snd_pcm_direct_open_secondary_client(snd_pcm_t **spcmp, snd_pcm_direct_t *dm
        dmix->slave_buffer_size = spcm->buffer_size;
        dmix->slave_period_size = dmix->shmptr->s.period_size;
        dmix->slave_boundary = spcm->boundary;
-       dmix->recoveries = dmix->shmptr->recoveries;
+       dmix->recoveries = dmix->shmptr->s.recoveries;
 
        ret = snd_pcm_mmap(spcm);
        if (ret < 0) {

diff --git a/src/pcm/pcm_direct.h b/src/pcm/pcm_direct.h
index 24e85f0..582f055 100644 (file)
--- a/src/pcm/pcm_direct.h
+++ b/src/pcm/pcm_direct.h
@@ -66,7 +66,6 @@ typedef struct {
        char socket_name[256];                  /* name of communication socket */
        snd_pcm_type_t type;                    /* PCM type (currently only hw) */
        int use_server;
-       unsigned int recoveries;                /* no of executed recoveries on slave*/
        struct {
                unsigned int format;
                snd_interval_t rate;
@@ -95,7 +94,7 @@ typedef struct {
                unsigned int stop_threshold;    
                unsigned int silence_threshold;
                unsigned int silence_size;
-               unsigned int xfer_align; /* not used */
+               unsigned int recoveries;        /* no of executed recoveries on slave*/
                unsigned long long boundary;
                unsigned int info;
                unsigned int msbits;