audio: extend -audio to allow creating a default backend

If "-audio BACKEND" is used without a model, the resulting backend
will be used whenever the audiodev property is not specified.

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

1 files changed, 21 insertions, 8 deletions

diff --git a/qemu-options.hx b/qemu-options.hx
index 840b83d237..54a7e94970 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -728,20 +728,22 @@ ERST
 
 
 DEF("audio", HAS_ARG, QEMU_OPTION_audio,
+    "-audio [driver=]driver[,prop[=value][,...]]\n"
+    "                specifies default audio backend when `audiodev` is not\n"
+    "                used to create a machine or sound device;"
+    "                options are the same as for -audiodev\n"
     "-audio [driver=]driver,model=value[,prop[=value][,...]]\n"
     "                specifies the audio backend and device to use;\n"
     "                apart from 'model', options are the same as for -audiodev.\n"
     "                use '-audio model=help' to show possible devices.\n",
     QEMU_ARCH_ALL)
 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 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.
+``-audio [driver=]driver[,model=value][,prop[=value][,...]]``
+    If the ``model`` option is specified, ``-audio`` is a shortcut
+    for configuring both the guest audio hardware and the host audio
+    backend in one go. The guest hardware model can be set with
+    ``model=modelname``.  Use ``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:
@@ -750,6 +752,17 @@ SRST
 
         |qemu_system| -audiodev pa,id=pa -device sb16,audiodev=pa
         |qemu_system| -audio pa,model=sb16
+
+    If the ``model`` option is not specified, ``-audio`` is used to
+    configure a default audio backend that will be used whenever the
+    ``audiodev`` property is not set on a device or machine.  In
+    particular, ``-audio none`` ensures that no audio is produced even
+    for machines that have embedded sound hardware.
+
+    In both cases, the driver option is the same as with the corresponding
+    ``-audiodev`` option below.  Use ``driver=help`` to list the available
+    drivers.
+
 ERST
 
 DEF("audiodev", HAS_ARG, QEMU_OPTION_audiodev,