Allow user to set qube audio volume

This is the `pacat-simple-vchan` core part of the patch to introduce a
`-V volume` command line option. It is used by `qvm-start-daemon` and
salt formulas.

resolves: QubesOS/qubes-issues#2724

Author: alimirjamali

pulse/pacat-simple-vchan.c

@@ -730,6 +730,8 @@ static bool connect_disconnect_rec_stream(
 static void context_state_callback(pa_context *c, void *userdata) {
     struct userdata *u = userdata;
     pa_stream_flags_t flags = 0;
+    pa_cvolume cvolume = {1, {u->volume}};
+    pa_cvolume *vol = (u->volume != -1) ? &cvolume : NULL;
 
     assert(c);
 
@@ -773,7 +775,7 @@ static void context_state_callback(pa_context *c, void *userdata) {
             if (verbose > 1)
                 flags |= PA_STREAM_AUTO_TIMING_UPDATE | PA_STREAM_INTERPOLATE_TIMING;
 
-            if (pa_stream_connect_playback(u->play_stream, u->play_device, bufattr, flags, NULL /* volume */, NULL) < 0) {
+            if (pa_stream_connect_playback(u->play_stream, u->play_device, bufattr, flags, vol /* volume */, NULL) < 0) {
                 pacat_log("pa_stream_connect_playback() failed: %s", pa_strerror(pa_context_errno(c)));
                 goto fail;
             }
@@ -1132,6 +1134,7 @@ static _Noreturn void usage(char *arg0, int arg) {
     fprintf(stream, "  -v - verbose logging (a lot of output, may affect performance)\n");
     fprintf(stream, "  -t size - target playback buffer fill, implies -l, default %d\n",
             custom_bufattr.tlength);
+    fprintf(stream, "  -V volume - set the target playback volume\n");
     fprintf(stream, "  -h - print this message\n");
     if (fflush(NULL) || ferror(stdout) || ferror(stderr))
         exit(1);
@@ -1151,9 +1154,10 @@ int main(int argc, char *argv[])
     char *endptr;
 
     memset(&u, 0, sizeof(u));
+    u.volume = -1;  // by default the volume is not readjusted
     if (argc <= 2)
         usage(argv[0], 1);
-    while ((i = getopt(argc, argv, "+lnbvt:h")) != -1) {
+    while ((i = getopt(argc, argv, "+lnbvt:V:h")) != -1) {
         switch (i) {
             case 'l':
                 bufattr = &custom_bufattr;
@@ -1179,6 +1183,17 @@ int main(int argc, char *argv[])
                 bufattr = &custom_bufattr;
                 custom_bufattr.tlength = tlength;
                 break;
+            case 'V':
+                errno = 0;
+                u.volume = strtoul(optarg, &endptr, 0);
+                if (*endptr)
+                    errx(1, "Invalid -V argument: %s", optarg);
+                if (u.volume > 150)   // pluse accepts volume greater than 100%
+                    errno = ERANGE;
+                if (errno)
+                    err(1, "Invalid -V argument: %s", optarg);
+                u.volume = PA_VOLUME_NORM * u.volume / 100;
+                break;
             case 'h':
                 usage(argv[0], 0);
             default:
@@ -1205,7 +1220,6 @@ int main(int argc, char *argv[])
     if (create_pidfile(u.domid, &pidfile_path, &pidfile_fd) < 0)
         /* error already printed by create_pidfile() */
         exit(1);
-    goto main;
 
 main:
     u.ret = 1;

pulse/pacat-simple-vchan.h

@@ -25,6 +25,8 @@ struct userdata {
     char *play_device;
     char *rec_device;
 
+    long volume;
+
     pa_io_event* play_stdio_event;
     pa_io_event* rec_stdio_event;
     pa_io_event* play_ctrl_event;