qapi, audio: add query-audiodev command

Way back in QEMU 4.0, the -audiodev command line option was introduced
for configuring audio backends. This CLI option does not use QemuOpts
so it is not visible for introspection in 'query-command-line-options',
instead using the QAPI Audiodev type.  Unfortunately there is also no
QMP command that uses the Audiodev type, so it is not introspectable
with 'query-qmp-schema' either.

This introduces a 'query-audiodev' command that simply reflects back
the list of configured -audiodev command line options. This alone is
maybe not very useful by itself, but it makes Audiodev introspectable
via 'query-qmp-schema', so that libvirt (and other upper layer tools)
can discover the available audiodevs.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
[thuth: Update for upcoming QEMU v8.0, and use QAPI_LIST_PREPEND]
Message-Id: <20230123083957.20349-2-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

audio/audio.c

@@ -28,8 +28,10 @@
 #include "monitor/monitor.h"
 #include "qemu/timer.h"
 #include "qapi/error.h"
+#include "qapi/clone-visitor.h"
 #include "qapi/qobject-input-visitor.h"
 #include "qapi/qapi-visit-audio.h"
+#include "qapi/qapi-commands-audio.h"
 #include "qemu/cutils.h"
 #include "qemu/module.h"
 #include "qemu/help_option.h"
@@ -2311,3 +2313,13 @@ size_t audio_rate_get_bytes(RateCtl *rate, struct audio_pcm_info *info,
 
     return bytes;
 }
+
+AudiodevList *qmp_query_audiodevs(Error **errp)
+{
+    AudiodevList *ret = NULL;
+    AudiodevListEntry *e;
+    QSIMPLEQ_FOREACH(e, &audiodevs, next) {
+        QAPI_LIST_PREPEND(ret, QAPI_CLONE(Audiodev, e->dev));
+    }
+    return ret;
+}

qapi/audio.json

@@ -443,3 +443,16 @@
     'sndio':     'AudiodevSndioOptions',
     'spice':     'AudiodevGenericOptions',
     'wav':       'AudiodevWavOptions' } }
+
+##
+# @query-audiodevs:
+#
+# Returns information about audiodev configuration
+#
+# Returns: array of @Audiodev
+#
+# Since: 8.0
+#
+##
+{ 'command': 'query-audiodevs',
+  'returns': ['Audiodev'] }