audio: add help option for -audio and -audiodev

add a simple help option for -audio and -audiodev
to show the list of available drivers, and document them.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Message-Id: <20220908081441.7111-1-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

audio/audio.c

@@ -32,6 +32,7 @@
 #include "qapi/qapi-visit-audio.h"
 #include "qemu/cutils.h"
 #include "qemu/module.h"
+#include "qemu/help_option.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/replay.h"
 #include "sysemu/runstate.h"
@@ -2101,10 +2102,28 @@ static void audio_validate_opts(Audiodev *dev, Error **errp)
     }
 }
 
+void audio_help(void)
+{
+    int i;
+
+    printf("Available audio drivers:\n");
+
+    for (i = 0; i < AUDIODEV_DRIVER__MAX; i++) {
+        audio_driver *driver = audio_driver_lookup(AudiodevDriver_str(i));
+        if (driver) {
+            printf("%s\n", driver->name);
+        }
+    }
+}
+
 void audio_parse_option(const char *opt)
 {
     Audiodev *dev = NULL;
 
+    if (is_help_option(opt)) {
+        audio_help();
+        exit(EXIT_SUCCESS);
+    }
     Visitor *v = qobject_input_visitor_new_str(opt, "driver", &error_fatal);
     visit_type_Audiodev(v, NULL, &dev, &error_fatal);
     visit_free(v);

audio/audio.h

@@ -171,6 +171,7 @@ void audio_sample_from_uint64(void *samples, int pos,
 void audio_define(Audiodev *audio);
 void audio_parse_option(const char *opt);
 bool audio_init_audiodevs(void);
+void audio_help(void);
 void audio_legacy_help(void);
 
 AudioState *audio_state_by_name(const char *name);

qemu-options.hx

@@ -704,10 +704,11 @@ SRST
 ``-audio [driver=]driver,model=value[,prop[=value][,...]]``
     This option is a shortcut for configuring both the guest audio
     hardware and the host audio backend in one go.
-    The host backend options are the same as with the corresponding
-    ``-audiodev`` options below. The guest hardware model can be set with
-    ``model=modelname``. Use ``model=help`` to list the available device
-    types.
+    The driver option is the same as with the corresponding ``-audiodev`` option below.
+    The guest hardware model can be set with ``model=modelname``.
+
+    Use ``driver=help`` to list the available drivers,
+    and ``model=help`` to list the available device types.
 
     The following two example do exactly the same, to show how ``-audio``
     can be used to shorten the command line length:
@@ -721,6 +722,7 @@ ERST
 DEF("audiodev", HAS_ARG, QEMU_OPTION_audiodev,
     "-audiodev [driver=]driver,id=id[,prop[=value][,...]]\n"
     "                specifies the audio backend to use\n"
+    "                Use ``-audiodev help`` to list the available drivers\n"
     "                id= identifier of the backend\n"
     "                timer-period= timer period in microseconds\n"
     "                in|out.mixing-engine= use mixing engine to mix streams inside QEMU\n"

softmmu/vl.c

@@ -2842,11 +2842,16 @@ void qemu_init(int argc, char **argv, char **envp)
                 audio_parse_option(optarg);
                 break;
             case QEMU_OPTION_audio: {
-                QDict *dict = keyval_parse(optarg, "driver", NULL, &error_fatal);
+                bool help;
                 char *model;
                 Audiodev *dev = NULL;
                 Visitor *v;
-
+                QDict *dict = keyval_parse(optarg, "driver", &help, &error_fatal);
+                if (help || (qdict_haskey(dict, "driver") &&
+                             is_help_option(qdict_get_str(dict, "driver")))) {
+                    audio_help();
+                    exit(EXIT_SUCCESS);
+                }
                 if (!qdict_haskey(dict, "id")) {
                     qdict_put_str(dict, "id", "audiodev0");
                 }