audio: exit(1) if audio backend failed to be found or initialized

If you specify a known backend but it isn't compiled in, or failed to
initialize, you get a simple warning and the "none" backend as a
fallback, and QEMU runs happily:

$ qemu-system-x86_64 -audiodev id=audio,driver=dsound
audio: Unknown audio driver `dsound'
audio: warning: Using timer based audio emulation
...

Instead, QEMU should fail to start:
$ qemu-system-x86_64 -audiodev id=audio,driver=dsound
audio: Unknown audio driver `dsound'
$

Resolves:
https://bugzilla.redhat.com/show_bug.cgi?id=1983493

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20220822131021.975656-1-marcandre.lureau@redhat.com>

audio/audio.c

@@ -1743,7 +1743,6 @@ static AudioState *audio_init(Audiodev *dev, const char *name)
         atexit(audio_cleanup);
         atexit_registered = true;
     }
-    QTAILQ_INSERT_TAIL(&audio_states, s, list);
 
     s->ts = timer_new_ns(QEMU_CLOCK_VIRTUAL, audio_timer, s);
 
@@ -1769,6 +1768,10 @@ static AudioState *audio_init(Audiodev *dev, const char *name)
         } else {
             dolog ("Unknown audio driver `%s'\n", drvname);
         }
+        if (!done) {
+            free_audio_state(s);
+            return NULL;
+        }
     } else {
         for (i = 0; audio_prio_list[i]; i++) {
             AudiodevListEntry *e = audiodev_find(&head, audio_prio_list[i]);
@@ -1806,6 +1809,7 @@ static AudioState *audio_init(Audiodev *dev, const char *name)
                "(Audio can continue looping even after stopping the VM)\n");
     }
 
+    QTAILQ_INSERT_TAIL(&audio_states, s, list);
     QLIST_INIT (&s->card_head);
     vmstate_register (NULL, 0, &vmstate_audio, s);
     return s;
@@ -2119,13 +2123,17 @@ void audio_define(Audiodev *dev)
     QSIMPLEQ_INSERT_TAIL(&audiodevs, e, next);
 }
 
-void audio_init_audiodevs(void)
+bool audio_init_audiodevs(void)
 {
     AudiodevListEntry *e;
 
     QSIMPLEQ_FOREACH(e, &audiodevs, next) {
-        audio_init(e->dev, NULL);
+        if (!audio_init(e->dev, NULL)) {
+            return false;
         }
+    }
+
+    return true;
 }
 
 audsettings audiodev_to_audsettings(AudiodevPerDirectionOptions *pdo)

audio/audio.h

@@ -170,7 +170,7 @@ void audio_sample_from_uint64(void *samples, int pos,
 
 void audio_define(Audiodev *audio);
 void audio_parse_option(const char *opt);
-void audio_init_audiodevs(void);
+bool audio_init_audiodevs(void);
 void audio_legacy_help(void);
 
 AudioState *audio_state_by_name(const char *name);

softmmu/vl.c

@@ -1885,7 +1885,9 @@ static void qemu_create_early_backends(void)
      * setting machine properties, so they can be referred to.
      */
     configure_blockdev(&bdo_queue, machine_class, snapshot);
-    audio_init_audiodevs();
+    if (!audio_init_audiodevs()) {
+        exit(1);
+    }
 }