Allow usage of legacy 3rd-party interface drivers

In the patch [1] we changed definition of the abstract method
"plug" in the LinuxInterfaceDriver class.
That broke e.g. 3rd-party drivers which still don't accept this
new parameter called "link_up" in the plug_new method.

So this patch fixes this to make such legacy drivers to be still working
with the new base interface driver class.

This commit also marks such definition of the plug_new method as
deprecated. Possibility of using it without accepting link_up parameter
will be removed in the "W" release of the OpenStack.

[1] https://review.opendev.org/#/c/707406/

Change-Id: Icd555987a1a57ca0b31fa7e4e830583d6c69c861
Closes-Bug: #1879307

neutron/agent/linux/interface.py

@@ -264,8 +264,9 @@ class LinuxInterfaceDriver(object):
              bridge=None, namespace=None, prefix=None, mtu=None, link_up=True):
         if not ip_lib.device_exists(device_name,
                                     namespace=namespace):
-            self.plug_new(network_id, port_id, device_name, mac_address,
-                          bridge, namespace, prefix, mtu, link_up)
+            self._safe_plug_new(
+                network_id, port_id, device_name, mac_address, bridge,
+                namespace, prefix, mtu, link_up)
         else:
             LOG.info("Device %s already exists", device_name)
             if mtu:
@@ -274,6 +275,22 @@ class LinuxInterfaceDriver(object):
             else:
                 LOG.warning("No MTU configured for port %s", port_id)
 
+    def _safe_plug_new(self, network_id, port_id, device_name, mac_address,
+            bridge=None, namespace=None, prefix=None, mtu=None, link_up=True):
+        try:
+            self.plug_new(
+                network_id, port_id, device_name, mac_address, bridge,
+                namespace, prefix, mtu, link_up)
+        except TypeError:
+            LOG.warning("Interface driver's plug_new() method should now "
+                        "accept additional optional parameter 'link_up'. "
+                        "Usage of plug_new() method which takes from 5 to 9 "
+                        "positional arguments is now deprecated and will not "
+                        "be possible in W release.")
+            self.plug_new(
+                network_id, port_id, device_name, mac_address, bridge,
+                namespace, prefix, mtu)
+
     @abc.abstractmethod
     def unplug(self, device_name, bridge=None, namespace=None, prefix=None):
         """Unplug the interface."""

neutron/tests/unit/agent/linux/test_interface.py

@@ -58,6 +58,17 @@ class FakePort(object):
     network_id = network.id
 
 
+class FakeLegacyInterfaceDriver(interface.LinuxInterfaceDriver):
+
+    def plug_new(self, network_id, port_id, device_name, mac_address,
+                 bridge=None, namespace=None, prefix=None, mtu=None):
+        """This is legacy method which don't accepts link_up argument."""
+        pass
+
+    def unplug(self, device_name, bridge=None, namespace=None, prefix=None):
+        pass
+
+
 class TestBase(base.BaseTestCase):
     def setUp(self):
         super(TestBase, self).setUp()
@@ -661,3 +672,20 @@ class TestBridgeInterfaceDriver(TestBase):
 
         self.ip_dev.assert_has_calls([mock.call('tap0', namespace=None),
                                       mock.call().link.delete()])
+
+
+class TestLegacyDriver(TestBase):
+
+    def test_plug(self):
+        self.device_exists.return_value = False
+        with mock.patch('neutron.agent.linux.interface.LOG.warning') as log:
+            driver = FakeLegacyInterfaceDriver(self.conf)
+            try:
+                driver.plug(
+                    '01234567-1234-1234-99', 'port-1234', 'tap0',
+                    'aa:bb:cc:dd:ee:ff')
+            except TypeError:
+                self.fail("LinuxInterfaceDriver class can not call properly "
+                          "plug_new method from the legacy drivers that "
+                          "do not accept 'link_up' parameter.")
+            log.assert_called_once()

releasenotes/notes/Deprecate-plug_new-method-without-link_up-parameter-27f8310eb1e1910a.yaml

@@ -0,0 +1,10 @@
+---
+deprecations:
+  - |
+    Abstract method ``plug_new`` from the
+    neutron.agent.linux.interface.LinuxInterfaceDriver class now accepts
+    an optional parameter ``link_up``.
+    Usage of this method, which takes from 5 to 9 positional arguments, without
+    ``link_up`` is now deprecated and will not be possible starting in the W
+    release. Third-party drivers which inherit from this base class should update
+    the implementation of their ``plug_new`` method.