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)

2 files changed, 31 insertions, 13 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.