libvirt-vif: Allow to configure a script on bridge interface

While running with libvirt-xen driver, it is possible to have the Xen
toolstack running a different script than the default on a vif. This patch
allow Nova to change this script.

Also do not set script to the empty string '' in designer.py for a linux
bridge. The empty string for script does not appear to be use anywhere in
the libvirt code when the vif is a bridge.

Change-Id: Ib6d6542d22decccfa68a058d362a42d60e6c2cca
Partial-Bug: #1461642

nova/tests/unit/virt/libvirt/test_config.py

@@ -1243,6 +1243,21 @@ class LibvirtConfigGuestInterfaceTest(LibvirtConfigBaseTest):
               </virtualport>
             </interface>""")
 
+    def test_config_bridge_xen(self):
+        obj = config.LibvirtConfigGuestInterface()
+        obj.net_type = "bridge"
+        obj.source_dev = "br0"
+        obj.mac_addr = "CA:FE:BE:EF:CA:FE"
+        obj.script = "/path/to/test-vif-openstack"
+
+        xml = obj.to_xml()
+        self.assertXmlEqual(xml, """
+            <interface type="bridge">
+              <mac address="CA:FE:BE:EF:CA:FE"/>
+              <source bridge="br0"/>
+              <script path="/path/to/test-vif-openstack"/>
+            </interface>""")
+
     def test_config_8021Qbh(self):
         obj = config.LibvirtConfigGuestInterface()
         obj.net_type = "direct"

nova/virt/libvirt/config.py

@@ -1173,6 +1173,10 @@ class LibvirtConfigGuestInterface(LibvirtConfigGuestDevice):
             dev.append(etree.Element("source", type=self.vhostuser_type,
                                      mode=self.vhostuser_mode,
                                      path=self.vhostuser_path))
+        elif self.net_type == "bridge":
+            dev.append(etree.Element("source", bridge=self.source_dev))
+            if self.script is not None:
+                dev.append(etree.Element("script", path=self.script))
         else:
             dev.append(etree.Element("source", bridge=self.source_dev))
 

nova/virt/libvirt/designer.py

@@ -43,7 +43,6 @@ def set_vif_host_backend_bridge_config(conf, brname, tapname=None):
     conf.source_dev = brname
     if tapname:
         conf.target_dev = tapname
-    conf.script = ""
 
 
 def set_vif_host_backend_ethernet_config(conf, tapname):