Add camilla_exit_cmd to allow a program to run just before the

camilladsp process is closed.  Mainly for storing gain and mute but
can be used for whatever.

asound.conf

@@ -167,6 +167,21 @@ pcm.camilladsp {
       # raspberry pi to turn on your amp for example.
       start_cmd "/path/to/start_command"
 
+      # An option not directly related to camilladsp.  A command to run when
+      # the CamillaDSP process is closed.  (Meaning when a playback program 
+      # closes the audio device or changes the HW params.)  Use it for 
+      # whatever you want.  A good example is storing the gain and mute 
+      # settings of CamillaDSP for use with the vol_file option below.
+      #
+      # Note this command is called just before the CamillaDSP process is 
+      # closed. That is not necessarily when you are done listening to music.
+      # So unlike the start_cmd this might not work well as a signal to turn 
+      # off your amp.  Also note that CamillaDSP is still expecting audio
+      # while this command is running so it may cause a harmless warning
+      # about a buffer underrun to be emitted by CamillaDSP if you have
+      # CamillaDSP's log level set sufficiently high.
+      camilla_exit_cmd "/path/to/camilla_exit_command"
+
       # Volume Parameter Passing Option
       # This options allows the plugin to pass gain and mute options on the
       # command line to CamillaDSP in case one uses CamillaDSP's Volume or
@@ -183,13 +198,12 @@ pcm.camilladsp {
       # integer >= 0.  If > 0 the -m (mute) option is passed to CamillaDSP.
       # If == 0 the -m is omitted.
       #
-      # To be useful another means of updating this file will have to exist
-      # such as a program that polls CamillaDSP's websocket for volume and
-      # mute values and writes them to this file.
-      #
       # If the file is missing or improperly formatted the plugin will
       # thrown an error during HW parameter setup.
-      # As this requires extra software to be useful it is commented out
-      # by default in this example asound.conf.
-      #vol_file "/path/to/volume_file_with_gain_and_mute_values"
+      #
+      # To be useful another means of updating this file will have to exist.
+      # One possibility is a program called by the exit_cmd option that 
+      # queries CamillaDSP's websocket for volume and mute values and writes 
+      # them to this file.
+      vol_file "/path/to/volume_file_with_gain_and_mute_values"
 }

libasound_module_pcm_cdsp.c

@@ -208,6 +208,9 @@ typedef struct {
   bool first_revent;
   // A command to run at init - turn on audio system for example
   char *start_cmd;
+  // A command to run just before the CamillaDSP process is ended
+  // A good time to update the gain and mute values for example
+  char *camilla_exit_cmd;
 } cdsp_t;
 
 #if SND_LIB_VERSION < 0x010106
@@ -762,6 +765,8 @@ static void free_cdsp(cdsp_t **pcm) {
     free((void *)(*pcm)->ext_samp_token);
   if((*pcm)->start_cmd)
     free((void *)(*pcm)->start_cmd);
+  if((*pcm)->camilla_exit_cmd)
+    free((void *)(*pcm)->camilla_exit_cmd);
   pthread_mutex_destroy(&(*pcm)->mutex);
   pthread_cond_destroy(&(*pcm)->pause_cond);
   free((void *)*pcm);
@@ -809,6 +814,15 @@ static int cdsp_hw_params(snd_pcm_ioplug_t *io, snd_pcm_hw_params_t *params __at
 static int cdsp_hw_free(snd_pcm_ioplug_t *io) {
   cdsp_t *pcm = io->private_data;
   debug("Freeing HW\n");
+  int err = 0;
+  if(pcm->camilla_exit_cmd) {
+    debug("Calling camilla_exit_cmd: %s\n", pcm->camilla_exit_cmd);
+    // Call the camilla_exit_cmd 
+    err = system(pcm->camilla_exit_cmd);
+    if(err != 0) {
+      SNDERR("Error executing camilla_exit_cmd %s\n", pcm->camilla_exit_cmd);
+    }
+  } 
   debug("Stopping Camilla\n");
   if (close_transport(pcm) == -1)
     return -errno;
@@ -818,7 +832,8 @@ static int cdsp_hw_free(snd_pcm_ioplug_t *io) {
     waitpid(pcm->cpid, NULL, 0);
     pcm->cpid = -1;
   }
-  return 0;
+  if(err > 0) return -err;
+  return err;
 }
 
 // A check that get_boundary still works
@@ -1307,6 +1322,11 @@ SND_PCM_PLUGIN_DEFINE_FUNC(cdsp) {
       if((err = alloc_copy_string(&pcm->start_cmd, temp)) < 0) goto _err;
       continue;
     }
+    if(strcmp(id, "camilla_exit_cmd") == 0) {
+      if((err = snd_config_get_string(n, &temp)) < 0) goto _err;
+      if((err = alloc_copy_string(&pcm->camilla_exit_cmd, temp)) < 0) goto _err;
+      continue;
+    }
     err = -EINVAL;
     goto _err;
   }