Allow for creation of multiqueue taps

We need this for virtion multiqueue support with the kernel vRouter. Tap
created by nova and then passed in to the libvirt has to be multiqueue enabled.

Change-Id: I7170bf7c181b038bb3d70a3b86c87ee254d10efc
Partial-Bug: #1573067

nova/network/linux_net.py

@@ -1400,12 +1400,16 @@ def delete_ivs_vif_port(dev):
                   run_as_root=True)
 
 
-def create_tap_dev(dev, mac_address=None):
+def create_tap_dev(dev, mac_address=None, multiqueue=False):
     if not device_exists(dev):
         try:
             # First, try with 'ip'
-            utils.execute('ip', 'tuntap', 'add', dev, 'mode', 'tap',
-                          run_as_root=True, check_exit_code=[0, 2, 254])
+            if multiqueue:
+                cmd = ('ip', 'tuntap', 'add', dev, 'mode', 'tap',
+                       'multi_queue')
+            else:
+                cmd = ('ip', 'tuntap', 'add', dev, 'mode', 'tap')
+            utils.execute(*cmd, run_as_root=True, check_exit_code=[0, 2, 254])
         except processutils.ProcessExecutionError:
             # Second option: tunctl
             utils.execute('tunctl', '-b', '-t', dev, run_as_root=True)

nova/virt/libvirt/vif.py

@@ -727,9 +727,20 @@ def plug_vrouter(self, instance, vif):
 
         Bind the vif to a Contrail virtual port.
         """
+        def multiqueue_enabled(instance):
+            metadata = instance['system_metadata']
+            mq = metadata.get('image_hw_vif_multiqueue_enabled')
+            vcpus = 0 if 'vcpus' not in instance else instance['vcpus']
+
+            if mq and mq.lower() == 'true' and vcpus > 1:
+                return True
+            else:
+                return False
+
         dev = self.get_vif_devname(vif)
         try:
-            linux_net.create_tap_dev(dev)
+            linux_net.create_tap_dev(dev,
+                    multiqueue=multiqueue_enabled(instance))
             self._vrouter_port_add(instance, vif)
         except processutils.ProcessExecutionError:
             LOG.exception(_LE("Failed while plugging vif"), instance=instance)