tap: Allow specifying a bridge

The tap backend is already using qemu-bridge-helper to attach tap
interface to a bridge but (unlike the bridge backend) it always uses
the default bridge name - br0.

This adds a "br" property support to the tap backend.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Greg Kurz <groug@kaod.org>
Tested-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Jason Wang <jasowang@redhat.com>

3 files changed, 13 insertions, 6 deletions

diff --git a/net/tap.c b/net/tap.c
index 6abb962efd..b6896a7b7c 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -857,7 +857,9 @@ free_fail:
             return -1;
         }
 
-        fd = net_bridge_run_helper(tap->helper, DEFAULT_BRIDGE_INTERFACE,
+        fd = net_bridge_run_helper(tap->helper,
+                                   tap->has_br ?
+                                   tap->br : DEFAULT_BRIDGE_INTERFACE,
                                    errp);
         if (fd == -1) {
             return -1;
diff --git a/qapi-schema.json b/qapi-schema.json
index e50706111c..c3dcf11a4a 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2636,6 +2636,8 @@
 #
 # @downscript: #optional script to shut down the interface
 #
+# @br: #optional bridge name (since 2.8)
+#
 # @helper: #optional command to execute to configure bridge
 #
 # @sndbuf: #optional send buffer limit. Understands [TGMKkb] suffixes.
@@ -2665,6 +2667,7 @@
     '*fds':        'str',
     '*script':     'str',
     '*downscript': 'str',
+    '*br':         'str',
     '*helper':     'str',
     '*sndbuf':     'size',
     '*vnet_hdr':   'bool',
diff --git a/qemu-options.hx b/qemu-options.hx
index 987d055481..01f01dfadc 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1598,10 +1598,11 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
     "                configure a host TAP network backend with ID 'str'\n"
 #else
     "-netdev tap,id=str[,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,downscript=dfile]\n"
-    "         [,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off]\n"
+    "         [,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off]\n"
     "         [,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n]\n"
     "         [,poll-us=n]\n"
     "                configure a host TAP network backend with ID 'str'\n"
+    "                connected to a bridge (default=" DEFAULT_BRIDGE_INTERFACE ")\n"
     "                use network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
     "                to configure it and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
     "                to deconfigure it\n"
@@ -1888,8 +1889,8 @@ processed and applied to -net user. Mixing them with the new configuration
 syntax gives undefined results. Their use for new applications is discouraged
 as they will be removed from future versions.
 
-@item -netdev tap,id=@var{id}[,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,helper=@var{helper}]
-@itemx -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,helper=@var{helper}]
+@item -netdev tap,id=@var{id}[,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
+@itemx -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
 Connect the host TAP network interface @var{name} to VLAN @var{n}.
 
 Use the network script @var{file} to configure it and the network script
@@ -1900,8 +1901,9 @@ automatically provides one. The default network configure script is
 to disable script execution.
 
 If running QEMU as an unprivileged user, use the network helper
-@var{helper} to configure the TAP interface. The default network
-helper executable is @file{/path/to/qemu-bridge-helper}.
+@var{helper} to configure the TAP interface and attach it to the bridge.
+The default network helper executable is @file{/path/to/qemu-bridge-helper}
+and the default bridge device is @file{br0}.
 
 @option{fd}=@var{h} can be used to specify the handle of an already
 opened host TAP interface.