stop setting mtu when plugging vhost-user ports

vhost-user is a userspace protocol to establish connectivity
between a virto-net frontend typically qemu and a
userspace virtio backend such as ovs with dpdk.

vhost-user interfaces exist only in userspace from the host perspective
and are not represented in the linux networking stack as kernel netdevs.
As a result attempting to set the mtu on a vhost-user interface
using ifconfig or ip link will fail with a device not found error.

- this change removes a call to _set_device_mtu when plugging
  vhost-user interfaces.
- this change prevents the device not found error from occurring
  which stopped vms booting with vhost-user interfaces
  due to an uncaught exception resulting in a failure to set the
  interface type in ovs.
- this change make creating vhost-user interface
  an atomic action.

This latent bug is only triggered when the mtu value is set to a
value other than 0 which was the default proir to mitaka.

Change-Id: I2e17723d5052d57cd1557bd8a173c06ea0dcb2d4
Closes-Bug: #1533876
(cherry picked from commit adf7ba61dd73fe4bfffa20295be9a4b1006a1fe6)

6 files changed, 95 insertions, 41 deletions

diff --git a/nova/network/linux_net.py b/nova/network/linux_net.py
index e2f40ff3cb..40064a05de 100644
--- a/nova/network/linux_net.py
+++ b/nova/network/linux_net.py
@@ -37,6 +37,7 @@ import six
 
 from nova import exception
 from nova.i18n import _, _LE, _LW
+from nova.network import model as network_model
 from nova import objects
 from nova import paths
 from nova.pci import utils as pci_utils
@@ -1365,15 +1366,34 @@ def _ovs_vsctl(args):
         raise exception.OvsConfigurationFailure(inner_exception=e)
 
 
-def create_ovs_vif_port(bridge, dev, iface_id, mac, instance_id, mtu=None):
-    _ovs_vsctl(['--', '--if-exists', 'del-port', dev, '--',
-                'add-port', bridge, dev,
-                '--', 'set', 'Interface', dev,
-                'external-ids:iface-id=%s' % iface_id,
-                'external-ids:iface-status=active',
-                'external-ids:attached-mac=%s' % mac,
-                'external-ids:vm-uuid=%s' % instance_id])
-    _set_device_mtu(dev, mtu)
+def _create_ovs_vif_cmd(bridge, dev, iface_id, mac,
+                        instance_id, interface_type=None):
+    cmd = ['--', '--if-exists', 'del-port', dev, '--',
+            'add-port', bridge, dev,
+            '--', 'set', 'Interface', dev,
+            'external-ids:iface-id=%s' % iface_id,
+            'external-ids:iface-status=active',
+            'external-ids:attached-mac=%s' % mac,
+            'external-ids:vm-uuid=%s' % instance_id]
+    if interface_type:
+        cmd += ['type=%s' % interface_type]
+    return cmd
+
+
+def create_ovs_vif_port(bridge, dev, iface_id, mac, instance_id,
+                        mtu=None, interface_type=None):
+    _ovs_vsctl(_create_ovs_vif_cmd(bridge, dev, iface_id,
+                                   mac, instance_id,
+                                   interface_type))
+    # Note at present there is no support for setting the
+    # mtu for vhost-user type ports.
+    if interface_type != network_model.OVS_VHOSTUSER_INTERFACE_TYPE:
+        _set_device_mtu(dev, mtu)
+    else:
+        LOG.debug("MTU not set on %(interface_name)s interface "
+                  "of type %(interface_type)s.",
+                  {'interface_name': dev,
+                   'interface_type': interface_type})
 
 
 def delete_ovs_vif_port(bridge, dev, delete_dev=True):
@@ -1382,10 +1402,6 @@ def delete_ovs_vif_port(bridge, dev, delete_dev=True):
         delete_net_dev(dev)
 
 
-def ovs_set_vhostuser_port_type(dev):
-    _ovs_vsctl(['--', 'set', 'Interface', dev, 'type=dpdkvhostuser'])
-
-
 def create_ivs_vif_port(dev, iface_id, mac, instance_id):
     utils.execute('ivs-ctl', 'add-port',
                    dev, run_as_root=True)
diff --git a/nova/network/model.py b/nova/network/model.py
index b28bc37aa9..8088ee8805 100644
--- a/nova/network/model.py
+++ b/nova/network/model.py
@@ -80,6 +80,8 @@ VIF_DETAILS_VHOSTUSER_OVS_PLUG = 'vhostuser_ovs_plug'
 # Specifies whether vhost-user socket should be used to
 # create a fp netdevice interface.
 VIF_DETAILS_VHOSTUSER_FP_PLUG = 'vhostuser_fp_plug'
+# ovs vhost user interface type name
+OVS_VHOSTUSER_INTERFACE_TYPE = 'dpdkvhostuser'
 
 # Constants for dictionary keys in the 'vif_details' field that are
 # valid for VIF_TYPE_TAP.
diff --git a/nova/tests/unit/network/test_linux_net.py b/nova/tests/unit/network/test_linux_net.py
index 2cbe02b4d3..8b35656d32 100644
--- a/nova/tests/unit/network/test_linux_net.py
+++ b/nova/tests/unit/network/test_linux_net.py
@@ -33,6 +33,7 @@ from nova import db
 from nova import exception
 from nova.network import driver
 from nova.network import linux_net
+from nova.network import model as network_model
 from nova import objects
 from nova import test
 from nova import utils
@@ -1216,13 +1217,37 @@ class LinuxNetworkTestCase(test.NoDBTestCase):
             linux_net._set_device_mtu('fake-dev')
             ex.assert_has_calls(calls)
 
-    def _ovs_vif_port(self, calls):
+    def _ovs_vif_port(self, calls, interface_type=None):
         with mock.patch.object(utils, 'execute', return_value=('', '')) as ex:
             linux_net.create_ovs_vif_port('fake-bridge', 'fake-dev',
                                           'fake-iface-id', 'fake-mac',
-                                          'fake-instance-uuid')
+                                          'fake-instance-uuid',
+                                          interface_type=interface_type)
             ex.assert_has_calls(calls)
 
+    def test_ovs_vif_port_cmd(self):
+        expected = ['--', '--if-exists',
+                    'del-port', 'fake-dev', '--', 'add-port',
+                    'fake-bridge', 'fake-dev',
+                    '--', 'set', 'Interface', 'fake-dev',
+                    'external-ids:iface-id=fake-iface-id',
+                    'external-ids:iface-status=active',
+                    'external-ids:attached-mac=fake-mac',
+                    'external-ids:vm-uuid=fake-instance-uuid'
+                ]
+        cmd = linux_net._create_ovs_vif_cmd('fake-bridge', 'fake-dev',
+                                            'fake-iface-id', 'fake-mac',
+                                            'fake-instance-uuid')
+
+        self.assertEqual(expected, cmd)
+
+        expected += ['type=fake-type']
+        cmd = linux_net._create_ovs_vif_cmd('fake-bridge', 'fake-dev',
+                                            'fake-iface-id', 'fake-mac',
+                                            'fake-instance-uuid',
+                                            'fake-type')
+        self.assertEqual(expected, cmd)
+
     def test_ovs_vif_port(self):
         calls = [
                 mock.call('ovs-vsctl', '--timeout=120', '--', '--if-exists',
@@ -1237,6 +1262,22 @@ class LinuxNetworkTestCase(test.NoDBTestCase):
                 ]
         self._ovs_vif_port(calls)
 
+    @mock.patch.object(linux_net, '_ovs_vsctl')
+    @mock.patch.object(linux_net, '_create_ovs_vif_cmd')
+    @mock.patch.object(linux_net, '_set_device_mtu')
+    def test_ovs_vif_port_with_type_vhostuser(self, mock_set_device_mtu,
+                                              mock_create_cmd, mock_vsctl):
+        linux_net.create_ovs_vif_port(
+            'fake-bridge',
+            'fake-dev', 'fake-iface-id', 'fake-mac',
+            "fake-instance-uuid", mtu=1500,
+            interface_type=network_model.OVS_VHOSTUSER_INTERFACE_TYPE)
+        mock_create_cmd.assert_called_once_with('fake-bridge',
+            'fake-dev', 'fake-iface-id', 'fake-mac',
+            "fake-instance-uuid", network_model.OVS_VHOSTUSER_INTERFACE_TYPE)
+        self.assertFalse(mock_set_device_mtu.called)
+        self.assertTrue(mock_vsctl.called)
+
     def test_ovs_vif_port_with_mtu(self):
         self.flags(network_device_mtu=10000)
         calls = [
@@ -1377,16 +1418,6 @@ class LinuxNetworkTestCase(test.NoDBTestCase):
         self.assertEqual(2, len(executes))
         self.mox.UnsetStubs()
 
-    def test_ovs_set_vhostuser_type(self):
-        calls = [
-                 mock.call('ovs-vsctl', '--timeout=120', '--', 'set',
-                           'Interface', 'fake-dev', 'type=dpdkvhostuser',
-                           run_as_root=True)
-                 ]
-        with mock.patch.object(utils, 'execute', return_value=('', '')) as ex:
-            linux_net.ovs_set_vhostuser_port_type('fake-dev')
-            ex.assert_has_calls(calls)
-
     @mock.patch('os.path.exists', return_value=True)
     @mock.patch('nova.utils.execute')
     def test_remove_bridge(self, mock_execute, mock_exists):
diff --git a/nova/tests/unit/virt/libvirt/test_vif.py b/nova/tests/unit/virt/libvirt/test_vif.py
index bf33eab910..6f48247b62 100644
--- a/nova/tests/unit/virt/libvirt/test_vif.py
+++ b/nova/tests/unit/virt/libvirt/test_vif.py
@@ -1313,22 +1313,19 @@ class LibvirtVifTestCase(test.NoDBTestCase):
     def test_vhostuser_ovs_plug(self):
 
         calls = {
-                'create_ovs_vif_port': [mock.call(
-                                      'br0', 'usv-xxx-yyy-zzz',
-                                      'aaa-bbb-ccc', 'ca:fe:de:ad:be:ef',
-                                      'f0000000-0000-0000-0000-000000000001',
-                                      9000)],
-                 'ovs_set_vhostuser_port_type': [mock.call('usv-xxx-yyy-zzz')]
+            'create_ovs_vif_port': [
+                 mock.call(
+                     'br0', 'usv-xxx-yyy-zzz',
+                     'aaa-bbb-ccc', 'ca:fe:de:ad:be:ef',
+                     'f0000000-0000-0000-0000-000000000001', 9000,
+                     interface_type=network_model.OVS_VHOSTUSER_INTERFACE_TYPE
+                 )]
         }
-        with test.nested(
-                mock.patch.object(linux_net, 'create_ovs_vif_port'),
-                mock.patch.object(linux_net, 'ovs_set_vhostuser_port_type')
-        ) as (create_ovs_vif_port, ovs_set_vhostuser_port_type):
+        with mock.patch.object(linux_net,
+                               'create_ovs_vif_port') as create_ovs_vif_port:
             d = vif.LibvirtGenericVIFDriver()
             d.plug_vhostuser(self.instance, self.vif_vhostuser_ovs)
             create_ovs_vif_port.assert_has_calls(calls['create_ovs_vif_port'])
-            ovs_set_vhostuser_port_type.assert_has_calls(
-                                        calls['ovs_set_vhostuser_port_type'])
 
     def test_vhostuser_ovs_unplug(self):
         calls = {
diff --git a/nova/virt/libvirt/vif.py b/nova/virt/libvirt/vif.py
index ec05a53e74..576c0ae5a4 100644
--- a/nova/virt/libvirt/vif.py
+++ b/nova/virt/libvirt/vif.py
@@ -677,10 +677,11 @@ class LibvirtGenericVIFDriver(object):
         port_name = os.path.basename(
             vif['details'][network_model.VIF_DETAILS_VHOSTUSER_SOCKET])
         mtu = vif['network'].get_meta('mtu')
-        linux_net.create_ovs_vif_port(self.get_bridge_name(vif),
-                                      port_name, iface_id, vif['address'],
-                                      instance.uuid, mtu)
-        linux_net.ovs_set_vhostuser_port_type(port_name)
+        linux_net.create_ovs_vif_port(
+            self.get_bridge_name(vif),
+            port_name, iface_id, vif['address'],
+            instance.uuid, mtu,
+            interface_type=network_model.OVS_VHOSTUSER_INTERFACE_TYPE)
 
     def plug_vhostuser(self, instance, vif):
         fp_plug = vif['details'].get(
diff --git a/releasenotes/notes/vhost-user-mtu-23d0af36a8adfa56.yaml b/releasenotes/notes/vhost-user-mtu-23d0af36a8adfa56.yaml
new file mode 100644
index 0000000000..642a7d2318
--- /dev/null
+++ b/releasenotes/notes/vhost-user-mtu-23d0af36a8adfa56.yaml
@@ -0,0 +1,7 @@
+---
+fixes:
+  - When plugging virtual interfaces of type vhost-user the MTU value will
+    not be applied to the interface by nova. vhost-user ports exist only in
+    userspace and are not backed by kernel netdevs, for this reason it is
+    not possible to set the mtu on a vhost-user interface using standard
+    tools such as ifconfig or ip link.