diff -r 1e3e30670ce4 tools/ioemu/target-i386-dm/qemu-ifup
--- a/tools/ioemu/target-i386-dm/qemu-ifup	Thu Dec 27 10:41:43 2007 +0000
+++ b/tools/ioemu/target-i386-dm/qemu-ifup	Thu Dec 27 13:13:39 2007 +0000
@@ -5,8 +5,12 @@
 
 echo 'config qemu network with xen bridge for ' $*
 
+ifconfig $1 0.0.0.0 up
+
 bridge=$2
 
+if [ -n "$bridge" ]
+then
 #
 # Old style bridge setup with netloop, used to have a bridge name
 # of xenbrX, enslaving pethX and vif0.X, and then configuring
@@ -25,13 +29,13 @@ bridge=$2
 #
 # This lets old config files work without modification
 #
-if [ ! -e "/sys/class/net/$bridge" ] && [ -z "${bridge##xenbr*}" ]
-then
-   if [ -e "/sys/class/net/eth${bridge#xenbr}/bridge" ]
+   if [ ! -e "/sys/class/net/$bridge" ] && [ -z "${bridge##xenbr*}" ]
    then
-      bridge="eth${bridge#xenbr}"
+      if [ -e "/sys/class/net/eth${bridge#xenbr}/bridge" ]
+      then
+         bridge="eth${bridge#xenbr}"
+      fi
    fi
+
+   brctl addif $bridge $1
 fi
-
-ifconfig $1 0.0.0.0 up
-brctl addif $bridge $1
diff -r 1e3e30670ce4 tools/ioemu/vl.c
--- a/tools/ioemu/vl.c	Thu Dec 27 10:41:43 2007 +0000
+++ b/tools/ioemu/vl.c	Thu Dec 27 13:13:39 2007 +0000
@@ -100,11 +100,6 @@
 #include "exec-all.h"
 
 #define DEFAULT_NETWORK_SCRIPT "/etc/xen/qemu-ifup"
-#ifdef _BSD
-#define DEFAULT_BRIDGE "bridge0"
-#else 
-#define DEFAULT_BRIDGE "xenbr0"
-#endif
 #ifdef __sun__
 #define SMBD_COMMAND "/usr/sfw/sbin/smbd"
 #else
@@ -4111,7 +4106,7 @@ static int net_client_init(const char *s
     if (!strcmp(device, "tap")) {
         char ifname[64];
         char setup_script[1024];
-        char bridge[16];
+        char bridge[16], *_bridge = NULL;
         int fd;
 
 	memset(ifname, 0, sizeof(ifname));
@@ -4129,10 +4124,10 @@ static int net_client_init(const char *s
             if (get_param_value(setup_script, sizeof(setup_script), "script", p) == 0) {
                 pstrcpy(setup_script, sizeof(setup_script), DEFAULT_NETWORK_SCRIPT);
             }
-            if (get_param_value(bridge, sizeof(bridge), "bridge", p) == 0) {
-                pstrcpy(bridge, sizeof(bridge), DEFAULT_BRIDGE);
-            }
-            ret = net_tap_init(vlan, ifname, setup_script, bridge);
+            if (get_param_value(bridge, sizeof(bridge), "bridge", p) > 0) {
+                _bridge = bridge;
+            }
+            ret = net_tap_init(vlan, ifname, setup_script, _bridge);
         }
     } else
 #endif
diff -r 1e3e30670ce4 tools/python/xen/xend/image.py
--- a/tools/python/xen/xend/image.py	Thu Dec 27 10:41:43 2007 +0000
+++ b/tools/python/xen/xend/image.py	Thu Dec 27 13:13:39 2007 +0000
@@ -485,13 +485,17 @@ class HVMImageHandler(ImageHandler):
             mac = devinfo.get('mac')
             if mac is None:
                 raise VmError("MAC address not specified or generated.")
-            bridge = devinfo.get('bridge', 'xenbr0')
+            bridge = devinfo.get('bridge')
             model = devinfo.get('model', 'rtl8139')
             ret.append("-net")
             ret.append("nic,vlan=%d,macaddr=%s,model=%s" %
                        (nics, mac, model))
             ret.append("-net")
-            ret.append("tap,vlan=%d,bridge=%s" % (nics, bridge))
+            if bridge is None:
+                bridge = ""
+            else:
+                bridge = (",bridge=%s" % (bridge))
+            ret.append("tap,vlan=%d%s" % (nics, bridge))
 
         return ret
 
diff -r 1e3e30670ce4 tools/xm-test/lib/XmTestLib/XenDevice.py
--- a/tools/xm-test/lib/XmTestLib/XenDevice.py	Thu Dec 27 10:41:43 2007 +0000
+++ b/tools/xm-test/lib/XmTestLib/XenDevice.py	Thu Dec 27 13:13:39 2007 +0000
@@ -179,8 +179,6 @@ class XenNetDevice(XenDevice):
 
         if domain.getDomainType() == "HVM":
             self.config["type"] = "ioemu"
-            if not self.config.has_key('bridge'):
-                self.config["bridge"] = "xenbr0"
 
         if self.config.has_key("ip"):
             self.setNetDevIP(ip=self.config["ip"])