libvirt: move checking CONF.my_ip to init_host()

Migrations use the libvirt driver's get_host_ip_addr() method to
determine the dest_host field of the migration object.
get_host_ip_addr() checks whether CONF.my_ip is actually assigned to
one of the host's interfaces. It does so by calling
get_machine_ips(), which iterates over all of the host's interfaces.
If the host has many interfaces, this can take a long time, and
introduces needless delays in processing the migration.
get_machine_ips() is only used to print a warning, so this patch moves
the get_machine_ips() call to a single method in init_host(). This
way, a warning is still emitted at compute service startup, and
migration progress is not needlessly slowed down.

NOTE(artom) While the following paragraph still applies, the poison
patch will not be backported. Stubbing out use of
netifaces.interfaces() is still a good thing to do, however.

This patch also has a chicken and egg problem with the patch on top of
it, which poisons use of netifaces.interfaces() in tests. While this
patch fixes all the tests that break with that poison, it starts
breaking different tests because of the move of get_machine_ips() into
init_host(). Therefore, while not directly related to the bug, this
patch also preventatively mocks or stubs out any use of
get_machine_ips() that will get poisoned with the subsequent patch.

Closes-bug: 1837075
Change-Id: I58a4038b04d5a9c28927d914e71609e4deea3d9f
(cherry picked from commit 30d8159)

Author: notartom

nova/tests/unit/virt/libvirt/fakelibvirt.py

@@ -1772,6 +1772,8 @@ def setUp(self):
 
         self.useFixture(
             fixtures.MockPatch('nova.virt.libvirt.utils.get_fs_info'))
+        self.useFixture(
+            fixtures.MockPatch('nova.compute.utils.get_machine_ips'))
 
         # libvirt driver needs to call out to the filesystem to get the
         # parent_ifname for the SRIOV VFs.

nova/tests/unit/virt/libvirt/test_driver.py

@@ -894,6 +894,8 @@ def setUp(self):
                       'resolve_driver_format',
                       imagebackend.Image._get_driver_format)
 
+        self.stub_out('nova.compute.utils.get_machine_ips', lambda: [])
+
         self.useFixture(fakelibvirt.FakeLibvirtFixture())
         self.test_instance = _create_test_instance()
         self.test_image_meta = {
@@ -13801,16 +13803,22 @@ def test_get_host_ip_addr(self):
 
     @mock.patch.object(libvirt_driver.LOG, 'warning')
     @mock.patch('nova.compute.utils.get_machine_ips')
-    def test_get_host_ip_addr_failure(self, mock_ips, mock_log):
+    def test_check_my_ip(self, mock_ips, mock_log):
         mock_ips.return_value = ['8.8.8.8', '75.75.75.75']
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), False)
-        drvr.get_host_ip_addr()
+        drvr._check_my_ip()
         mock_log.assert_called_once_with(u'my_ip address (%(my_ip)s) was '
                                          u'not found on any of the '
                                          u'interfaces: %(ifaces)s',
                                          {'ifaces': '8.8.8.8, 75.75.75.75',
                                           'my_ip': mock.ANY})
 
+    def test_init_host_checks_ip(self):
+        drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
+        with mock.patch.object(drvr, '_check_my_ip') as mock_check:
+            drvr.init_host('fake-host')
+            mock_check.assert_called_once_with()
+
     def test_conn_event_handler(self):
         drvr = libvirt_driver.LibvirtDriver(fake.FakeVirtAPI(), True)
         service_mock = mock.MagicMock()
@@ -21446,6 +21454,8 @@ def test_get_existing_mdevs_not_assigned(self, get_all_assigned_mdevs,
         self.assertEqual(set([uuids.mdev1]),
                          drvr._get_existing_mdevs_not_assigned())
 
+    @mock.patch('nova.compute.utils.get_machine_ips',
+                new=mock.Mock(return_value=[]))
     @mock.patch.object(nova.privsep.libvirt, 'create_mdev')
     @mock.patch.object(libvirt_driver.LibvirtDriver,
                        '_get_mdev_capable_devices')

nova/tests/unit/virt/test_virt_drivers.py

@@ -900,6 +900,7 @@ def setUp(self):
         # will try to execute some commands which hangs tests so let's just
         # stub out the unplug call to os-vif since we don't care about it.
         self.stub_out('os_vif.unplug', lambda a, kw: None)
+        self.stub_out('nova.compute.utils.get_machine_ips', lambda: [])
 
     def test_force_hard_reboot(self):
         self.flags(wait_soft_reboot_seconds=0, group='libvirt')

nova/virt/libvirt/driver.py

@@ -491,6 +491,8 @@ def init_host(self, host):
 
         self._check_file_backed_memory_support()
 
+        self._check_my_ip()
+
         if (CONF.libvirt.virt_type == 'lxc' and
                 not (CONF.libvirt.uid_maps and CONF.libvirt.gid_maps)):
             LOG.warning("Running libvirt-lxc without user namespaces is "
@@ -643,6 +645,13 @@ def _check_file_backed_memory_support(self):
                     'Running Nova with file_backed_memory requires '
                     'ram_allocation_ratio configured to 1.0')
 
+    def _check_my_ip(self):
+        ips = compute_utils.get_machine_ips()
+        if CONF.my_ip not in ips:
+            LOG.warning('my_ip address (%(my_ip)s) was not found on '
+                        'any of the interfaces: %(ifaces)s',
+                        {'my_ip': CONF.my_ip, 'ifaces': ", ".join(ips)})
+
     def _prepare_migration_flags(self):
         migration_flags = 0
 
@@ -3279,11 +3288,6 @@ def get_console_output(self, context, instance):
         return self._get_console_output_file(instance, console_path)
 
     def get_host_ip_addr(self):
-        ips = compute_utils.get_machine_ips()
-        if CONF.my_ip not in ips:
-            LOG.warning('my_ip address (%(my_ip)s) was not found on '
-                        'any of the interfaces: %(ifaces)s',
-                        {'my_ip': CONF.my_ip, 'ifaces': ", ".join(ips)})
         return CONF.my_ip
 
     def get_vnc_console(self, context, instance):