audio: reintroduce default audio backend for VNC

Make VNC use the default backend again if one is defined.
The recently introduced support for disabling the VNC audio
extension is still used, in case no default backend exists.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

audio/audio.c

@@ -1801,20 +1801,28 @@ out:
     return NULL;
 }
 
-bool AUD_register_card (const char *name, QEMUSoundCard *card, Error **errp)
+AudioState *audio_get_default_audio_state(Error **errp)
 {
-    if (!card->state) {
+    if (!default_audio_state) {
+        default_audio_state = audio_init(NULL, errp);
         if (!default_audio_state) {
-            default_audio_state = audio_init(NULL, errp);
-            if (!default_audio_state) {
-                if (!QSIMPLEQ_EMPTY(&audiodevs)) {
-                    error_append_hint(errp, "Perhaps you wanted to use -audio or set audiodev=%s?\n",
-                                      QSIMPLEQ_FIRST(&audiodevs)->dev->id);
-                }
-                return false;
+            if (!QSIMPLEQ_EMPTY(&audiodevs)) {
+                error_append_hint(errp, "Perhaps you wanted to use -audio or set audiodev=%s?\n",
+                                  QSIMPLEQ_FIRST(&audiodevs)->dev->id);
             }
         }
-        card->state = default_audio_state;
+    }
+
+    return default_audio_state;
+}
+
+bool AUD_register_card (const char *name, QEMUSoundCard *card, Error **errp)
+{
+    if (!card->state) {
+        card->state = audio_get_default_audio_state(errp);
+        if (!card->state) {
+            return false;
+        }
     }
 
     card->name = g_strdup (name);

audio/audio.h

@@ -176,6 +176,7 @@ void audio_init_audiodevs(void);
 void audio_help(void);
 
 AudioState *audio_state_by_name(const char *name, Error **errp);
+AudioState *audio_get_default_audio_state(Error **errp);
 const char *audio_get_id(QEMUSoundCard *card);
 
 #define DEFINE_AUDIO_PROPERTIES(_s, _f)         \

docs/about/removed-features.rst

@@ -460,12 +460,6 @@ in this case.
 Note that the default audio backend must be configured on the command
 line if the ``-nodefaults`` options is used.
 
-Creating vnc without ``audiodev=`` property (removed in 8.2)
-''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
-
-When using vnc, you should specify an ``audiodev=`` property if
-you plan to transmit audio through the VNC protocol.
-
 QEMU Machine Protocol (QMP) commands
 ------------------------------------
 

ui/vnc.c

@@ -4185,6 +4185,8 @@ void vnc_display_open(const char *id, Error **errp)
         if (!vd->audio_state) {
             goto fail;
         }
+    } else {
+        vd->audio_state = audio_get_default_audio_state(NULL);
     }
 
     device_id = qemu_opt_get(opts, "display");