Deprecate xenserver.vif_driver config option and change default

There are two in-tree options for the xenserver.vif_driver,
the bridge driver and the ovs driver. The XenAPI subteam has
confirmed that the bridge driver is for nova-network (which is
deprecated) and the ovs driver is for Neutron, and that's how
things are tested in CI.

Since we changed the default on use_neutron to be True for Ocata
we need to change the default on the vif_driver to be the ovs
driver so it works with the default config, which is Neutron.

We're deprecating the option though since we can use the use_neutron
option to decide which vif driver to load - which will make
deploying and configuring nova with xen as the backend simpler.

Change-Id: I599f3449f18d2821403961fb9d52e9a14dd3366b

nova/conf/xenserver.py

@@ -547,12 +547,21 @@ time, the launch expires and the instance(s) are set to 'error'
 state.
 """),
     cfg.StrOpt('vif_driver',
-        default='nova.virt.xenapi.vif.XenAPIBridgeDriver',
+        default='nova.virt.xenapi.vif.XenAPIOpenVswitchDriver',
+        deprecated_for_removal=True,
+        deprecated_since='15.0.0',
+        deprecated_reason="""
+There are only two in-tree vif drivers for XenServer. XenAPIBridgeDriver is for
+nova-network which is deprecated and XenAPIOpenVswitchDriver is for Neutron
+which is the default configuration for Nova since the 15.0.0 Ocata release. In
+the future the "use_neutron" configuration option will be used to determine
+which vif driver to use.
+""",
         help="""
 The XenAPI VIF driver using XenServer Network APIs.
 
-Provide a string value representing the VIF XenAPI bridge driver to
-use for bridging.
+Provide a string value representing the VIF XenAPI vif driver to use for
+plugging virtual network interfaces.
 
 Xen configuration uses bridging within the backend domain to allow
 all VMs to appear on the network as individual hosts. Bridge
@@ -561,9 +570,15 @@ the VIFs for the VM instances are plugged. If no VIF bridge driver
 is plugged, the bridge is not made available. This configuration
 option takes in a value for the VIF driver.
 
-NOTE:
-The XenAPIBridgeDriver should be used for running OVS or Bridge in
-XenServer.
+Possible values:
+
+* nova.virt.xenapi.vif.XenAPIOpenVswitchDriver (default)
+* nova.virt.xenapi.vif.XenAPIBridgeDriver (deprecated)
+
+Related options:
+
+* ``vlan_interface``
+* ``ovs_integration_bridge``
 """),
     # TODO(dharinic): Make this, a stevedore plugin
     cfg.StrOpt('image_upload_handler',

nova/tests/unit/virt/xenapi/stubs.py

@@ -396,6 +396,10 @@ def get_fake_session(error=None):
 class XenAPITestBase(test.TestCase):
     def setUp(self):
         super(XenAPITestBase, self).setUp()
+        # TODO(mriedem): The tests need to be fixed to work with the
+        # XenAPIOpenVswitchDriver vif driver.
+        self.flags(vif_driver='nova.virt.xenapi.vif.XenAPIBridgeDriver',
+                   group='xenserver')
         self.useFixture(ReplaceModule('XenAPI', fake))
         fake.reset()
 
@@ -403,5 +407,9 @@ class XenAPITestBase(test.TestCase):
 class XenAPITestBaseNoDB(test.NoDBTestCase):
     def setUp(self):
         super(XenAPITestBaseNoDB, self).setUp()
+        # TODO(mriedem): The tests need to be fixed to work with the
+        # XenAPIOpenVswitchDriver vif driver.
+        self.flags(vif_driver='nova.virt.xenapi.vif.XenAPIBridgeDriver',
+                   group='xenserver')
         self.useFixture(ReplaceModule('XenAPI', fake))
         fake.reset()

releasenotes/notes/deprecate-xenserver-vif-driver-option-12eb279c0c93c157.yaml

@@ -0,0 +1,13 @@
+---
+upgrade:
+  - |
+    The default value for the ``[xenserver]/vif_driver`` configuration option
+    has been changed to ``nova.virt.xenapi.vif.XenAPIOpenVswitchDriver`` to
+    match the default configuration of ``[DEFAULT]/use_neutron=True``.
+deprecations:
+  - |
+    The ``[xenserver]/vif_driver`` configuration option is deprecated for
+    removal. The ``XenAPIOpenVswitchDriver`` vif driver is used for Neutron and
+    the ``XenAPIBridgeDriver`` vif driver is used for nova-network, which
+    itself is deprecated. In the future, the ``use_neutron`` configuration
+    option will be used to determine which vif driver to load.