Added method XendDomain.privilegedDomain and use that inside DevController to

avoid hard-coding the domain ID 0.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

tools/python/xen/xend/XendDomain.py

@@ -284,6 +284,11 @@ class XendDomain:
                 pass
         return dominfo
 
+
+    def privilegedDomain(self):
+        return self.domains[PRIV_DOMAIN]
+
+ 
     def domain_unpause(self, id):
         """Unpause domain execution.
 

tools/python/xen/xend/server/DevController.py

@@ -189,8 +189,17 @@ class DevController:
         """
 
         import xen.xend.XendDomain
-        backdom = xen.xend.XendDomain.instance().domain_lookup_by_name(
-            sxp.child_value(config, 'backend', '0'))
+        xd = xen.xend.XendDomain.instance()
+
+        backdom_name = sxp.child_value(config, 'backend')
+        if backdom_name:
+            backdom = xd.domain_lookup_by_name(backdom_name)
+        else:
+            backdom = xd.privilegedDomain()
+
+        if not backdom:
+            raise VmError("Cannot configure device for unknown backend %s" %
+                          backdom_name)
 
         frontpath = self.frontendPath(devid)
         backpath  = self.backendPath(backdom, devid)