Check interface presence in new namespace

When an interface is moved to a new namespace, specially with OVS
internal ports, the interface first dissapears from any network
namespace and then is added again. ovs-vswitchd service detects
this interface change as reported in [1]. This delay is the cause
of the related bug, where some interfaces are not present when
the L3 agent needs to manipulate them.

[1]https://bugs.launchpad.net/neutron/+bug/1948832/comments/3

Conflicts:
    neutron/tests/functional/agent/linux/test_ip_lib.py

Closes-Bug: #1948832

Change-Id: I3af4d0afa784899689ccb595ce6ba64495431eb9
(cherry picked from commit ebc4766990)

neutron/agent/linux/ip_lib.py

@@ -443,6 +443,8 @@ class IpLinkCommand(IpDeviceCommandBase):
         privileged.set_link_attribute(
             self.name, self._parent.namespace, net_ns_fd=namespace)
         self._parent.namespace = namespace
+        common_utils.wait_until_true(lambda: self.exists, timeout=5,
+                                     sleep=0.5)
 
     def set_name(self, name):
         privileged.set_link_attribute(

neutron/tests/functional/agent/linux/test_ip_lib.py

@@ -1143,3 +1143,14 @@ class GetDevicesWithIpTestCase(functional_base.BaseSudoTestCase):
             ip_addresses = self._remove_loopback_interface(ip_addresses)
             ip_addresses = self._remove_ipv6_scope_link(ip_addresses)
             self.assertEqual(0, len(ip_addresses))
+
+
+class IpLinkCommandTestCase(IpLibTestFramework):
+
+    def test_set_netns(self):
+        device_name = ('int_' + uuidutils.generate_uuid())[
+                      :constants.DEVICE_NAME_MAX_LEN]
+        device = ip_lib.IPDevice(device_name, kind='dummy')
+        device.link.create()
+        namespace = self.useFixture(net_helpers.NamespaceFixture())
+        device.link.set_netns(namespace.name)

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

@@ -618,8 +618,9 @@ class TestIpLinkCommand(TestIPCmdBase):
         set_link_attribute.assert_called_once_with(
             self.parent.name, self.parent.namespace, state='down')
 
+    @mock.patch.object(priv_lib, 'interface_exists', return_value=True)
     @mock.patch.object(priv_lib, 'set_link_attribute')
-    def test_set_netns(self, set_link_attribute):
+    def test_set_netns(self, set_link_attribute, *args):
         original_namespace = self.parent.namespace
         self.link_cmd.set_netns('foo')
         set_link_attribute.assert_called_once_with(