audio: add module loading support

Make audio_driver_lookup() try load the module in case it doesn't find
the driver in the registry.  Also load all modules for -audio-help, so
the help output includes the help text for modular audio drivers.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20180306074053.22856-3-kraxel@redhat.com
diff --git a/audio/audio.c b/audio/audio.c
index 2384612..6eccdb1 100644
--- a/audio/audio.c
+++ b/audio/audio.c
@@ -68,9 +68,26 @@
             return d;
         }
     }
+
+    audio_module_load_one(name);
+    QLIST_FOREACH(d, &audio_drivers, next) {
+        if (strcmp(name, d->name) == 0) {
+            return d;
+        }
+    }
+
     return NULL;
 }
 
+static void audio_module_load_all(void)
+{
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(audio_prio_list); i++) {
+        audio_driver_lookup(audio_prio_list[i]);
+    }
+}
+
 struct fixed_settings {
     int enabled;
     int nb_voices;
@@ -1675,6 +1692,9 @@
 {
     struct audio_driver *d;
 
+    /* make sure we print the help text for modular drivers too */
+    audio_module_load_all();
+
     audio_process_options ("AUDIO", audio_options);
     QLIST_FOREACH(d, &audio_drivers, next) {
         if (d->options) {