Allow tap interface with multiqueue

When vif_type="tap" (such as when using calico),
attempting to create an instance using an image that has
the property hw_vif_multiqueue_enabled=True fails, because
the interface is always being created without multiqueue
flags.

This change checks if the property is defined and passes
the multiqueue parameter to create the tap interface
accordingly.

In case the multiqueue parameter is passed but the
vif_model is not virtio (or unspecified), the old
behavior is maintained.

Change-Id: I0307c43dcd0cace1620d2ac75925651d4ee2e96c
Closes-bug: #1893263

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

@@ -1057,10 +1057,71 @@ class LibvirtVifTestCase(test.NoDBTestCase):
     @mock.patch('nova.privsep.linux_net.device_exists', return_value=True)
     @mock.patch('nova.privsep.linux_net.set_device_mtu')
     @mock.patch('nova.privsep.linux_net.create_tap_dev')
-    def test_plug_tap(self, mock_create_tap_dev, mock_set_mtu,
+    def test_plug_tap_kvm_virtio(self, mock_create_tap_dev, mock_set_mtu,
                       mock_device_exists):
-        d = vif.LibvirtGenericVIFDriver()
+
-        d.plug(self.instance, self.vif_tap)
+        d1 = vif.LibvirtGenericVIFDriver()
+        ins = objects.Instance(
+            id=1, uuid='f0000000-0000-0000-0000-000000000001',
+            project_id=723, system_metadata={}
+        )
+        d1.plug(ins, self.vif_tap)
+        mock_create_tap_dev.assert_called_once_with('tap-xxx-yyy-zzz', None,
+                                                    multiqueue=False)
+
+        mock_create_tap_dev.reset_mock()
+
+        d2 = vif.LibvirtGenericVIFDriver()
+        mq_ins = objects.Instance(
+            id=1, uuid='f0000000-0000-0000-0000-000000000001',
+            project_id=723, system_metadata={
+                'image_hw_vif_multiqueue_enabled': 'True'
+            }
+        )
+        d2.plug(mq_ins, self.vif_tap)
+        mock_create_tap_dev.assert_called_once_with('tap-xxx-yyy-zzz', None,
+                                                    multiqueue=True)
+
+    @mock.patch('nova.privsep.linux_net.device_exists', return_value=True)
+    @mock.patch('nova.privsep.linux_net.set_device_mtu')
+    @mock.patch('nova.privsep.linux_net.create_tap_dev')
+    def test_plug_tap_mq_ignored_virt_type(
+            self, mock_create_tap_dev, mock_set_mtu, mock_device_exists):
+
+        self.flags(use_virtio_for_bridges=True,
+                   virt_type='xen',
+                   group='libvirt')
+
+        d1 = vif.LibvirtGenericVIFDriver()
+        ins = objects.Instance(
+            id=1, uuid='f0000000-0000-0000-0000-000000000001',
+            project_id=723, system_metadata={
+                'image_hw_vif_multiqueue_enabled': 'True'
+            }
+        )
+        d1.plug(ins, self.vif_tap)
+        mock_create_tap_dev.assert_called_once_with('tap-xxx-yyy-zzz',
+                                                    None,
+                                                    multiqueue=False)
+
+    @mock.patch('nova.privsep.linux_net.device_exists', return_value=True)
+    @mock.patch('nova.privsep.linux_net.set_device_mtu')
+    @mock.patch('nova.privsep.linux_net.create_tap_dev')
+    def test_plug_tap_mq_ignored_vif_model(
+            self, mock_create_tap_dev, mock_set_mtu, mock_device_exists):
+
+        d1 = vif.LibvirtGenericVIFDriver()
+        ins = objects.Instance(
+            id=1, uuid='f0000000-0000-0000-0000-000000000001',
+            project_id=723, system_metadata={
+                'image_hw_vif_multiqueue_enabled': 'True',
+                'image_hw_vif_model': 'e1000',
+            }
+        )
+        d1.plug(ins, self.vif_tap)
+        mock_create_tap_dev.assert_called_once_with('tap-xxx-yyy-zzz',
+                                                    None,
+                                                    multiqueue=False)
 
     def test_unplug_tap(self):
         d = vif.LibvirtGenericVIFDriver()

nova/virt/libvirt/vif.py

@@ -157,6 +157,24 @@ class LibvirtGenericVIFDriver(object):
             return vif['devname']
         return ("nic" + vif['id'])[:network_model.NIC_NAME_LEN]
 
+    def get_vif_model(self, image_meta=None, vif_model=None):
+
+        model = vif_model
+
+        # If the user has specified a 'vif_model' against the
+        # image then honour that model
+        if image_meta:
+            model = osinfo.HardwareProperties(image_meta).network_model
+
+        # If the virt type is KVM/QEMU/VZ(Parallels), then use virtio according
+        # to the global config parameter
+        if (model is None and CONF.libvirt.virt_type in
+                ('kvm', 'qemu', 'parallels') and
+                CONF.libvirt.use_virtio_for_bridges):
+            model = network_model.VIF_MODEL_VIRTIO
+
+        return model
+
     def get_base_config(self, instance, mac, image_meta,
                         inst_type, virt_type, vnic_type):
         # TODO(sahid): We should rewrite it. This method handles too
@@ -179,16 +197,9 @@ class LibvirtGenericVIFDriver(object):
 
         rx_queue_size = CONF.libvirt.rx_queue_size
 
-        # If the user has specified a 'vif_model' against the
+        # if model has already been defined,
-        # image then honour that model
+        # image_meta contents will override it
-        if image_meta:
+        model = self.get_vif_model(image_meta=image_meta, vif_model=model)
-            model = osinfo.HardwareProperties(image_meta).network_model
-
-        # If the virt type is KVM/QEMU/VZ(Parallels), then use virtio according
-        # to the global config parameter
-        if (model is None and virt_type in ('kvm', 'qemu', 'parallels') and
-                CONF.libvirt.use_virtio_for_bridges):
-            model = network_model.VIF_MODEL_VIRTIO
 
         if not is_vif_model_valid_for_virt(virt_type, model):
             raise exception.UnsupportedHardware(model=model, virt=virt_type)
@@ -244,10 +255,7 @@ class LibvirtGenericVIFDriver(object):
         """
         driver = None
         vhost_queues = None
-        if not isinstance(image_meta, objects.ImageMeta):
+        if self._requests_multiqueue(image_meta):
-            image_meta = objects.ImageMeta.from_dict(image_meta)
-        img_props = image_meta.properties
-        if img_props.get('hw_vif_multiqueue_enabled'):
             driver = 'vhost'
             max_tap_queues = self._get_max_tap_queues()
             if max_tap_queues:
@@ -258,6 +266,19 @@ class LibvirtGenericVIFDriver(object):
 
         return (driver, vhost_queues)
 
+    def _requests_multiqueue(self, image_meta):
+        """Check if multiqueue property is set in the image metadata."""
+
+        if not isinstance(image_meta, objects.ImageMeta):
+            image_meta = objects.ImageMeta.from_dict(image_meta)
+
+        img_props = image_meta.properties
+
+        if img_props.get('hw_vif_multiqueue_enabled'):
+            return True
+
+        return False
+
     def _get_max_tap_queues(self):
         # Note(sean-k-mooney): some linux distros have backported
         # changes for newer kernels which make the kernel version
@@ -641,7 +662,13 @@ class LibvirtGenericVIFDriver(object):
         """Plug a VIF_TYPE_TAP virtual interface."""
         dev = self.get_vif_devname(vif)
         mac = vif['details'].get(network_model.VIF_DETAILS_TAP_MAC_ADDRESS)
-        nova.privsep.linux_net.create_tap_dev(dev, mac)
+        image_meta = instance.image_meta
+        vif_model = self.get_vif_model(image_meta=image_meta)
+        # TODO(ganso): explore whether multiqueue works for other vif models
+        # that go through this code path.
+        multiqueue = (self._requests_multiqueue(image_meta) and
+                      vif_model == network_model.VIF_MODEL_VIRTIO)
+        nova.privsep.linux_net.create_tap_dev(dev, mac, multiqueue=multiqueue)
         network = vif.get('network')
         mtu = network.get_meta('mtu') if network else None
         nova.privsep.linux_net.set_device_mtu(dev, mtu)

releasenotes/notes/bug-1893263-769acadc4b6141d0.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Addressed an issue that prevented instances using multiqueue feature from
+    being created successfully when their vif_type is TAP.