iscsi: Add _get_device_link retry when waiting for /dev/disk/by-id/ to populate

Bug #1820007 documents failures to find /dev/disk/by-id/ symlinks
associated with encrypted volumes both in real world and CI
environments. These failures appear to be due to udev on these slow or
overloaded hosts failing to populate the required /dev/disk/by-id/
symlinks in time after the iSCSI volume has been connected.

This change seeks to avoid such failures by simply decorating
_get_device_link with the @utils.retry to hopefully allow udev time to
create the required symlinks under /dev/disk/by-id/.

Closes-Bug: #1820007
Change-Id: Ib9c8ebae7a6051e18538920139fecd123682a474

os_brick/initiator/connectors/iscsi.py

@@ -518,6 +518,7 @@ class ISCSIConnector(base.BaseLinuxConnector, base_iscsi.BaseISCSIConnector):
             with excutils.save_and_reraise_exception():
                 self._cleanup_connection(connection_properties, force=True)
 
+    @utils.retry(exceptions=(exception.VolumeDeviceNotFound))
     def _get_device_link(self, wwn, device, mpath):
         # These are the default symlinks that should always be there
         if mpath:

os_brick/tests/initiator/connectors/test_iscsi.py

@@ -1583,17 +1583,67 @@ Setting up iSCSI targets: unused
             mock.call('/dev/disk/by-id/dm-...'),
             mock.call('/dev/disk/by-id/scsi-wwn')])
 
+    @mock.patch('time.sleep')
     @mock.patch('os.path.realpath', return_value='/dev/sdz')
     @mock.patch('os.listdir', return_value=['dm-...', 'scsi-...'])
-    def test__get_device_link_not_found(self, listdir_mock, realpath_mock):
+    def test__get_device_link_not_found(self, listdir_mock, realpath_mock,
+                                        mock_time):
         self.assertRaises(exception.VolumeDeviceNotFound,
                           self.connector._get_device_link,
                           'wwn', '/dev/sda', None)
-        listdir_mock.assert_called_once_with('/dev/disk/by-id/')
-        realpath_mock.assert_has_calls([
-            mock.call('/dev/disk/by-id/scsi-wwn'),
-            mock.call('/dev/disk/by-id/dm-...'),
-            mock.call('/dev/disk/by-id/scsi-...')])
+        listdir_mock.assert_has_calls(3 * [mock.call('/dev/disk/by-id/')])
+        self.assertEqual(3, listdir_mock.call_count)
+        realpath_mock.assert_has_calls(
+            3 * [mock.call('/dev/disk/by-id/scsi-wwn'),
+                 mock.call('/dev/disk/by-id/dm-...'),
+                 mock.call('/dev/disk/by-id/scsi-...')])
+        self.assertEqual(9, realpath_mock.call_count)
+
+    @mock.patch('time.sleep')
+    @mock.patch('os.path.realpath')
+    @mock.patch('os.listdir', return_value=['dm-...', 'scsi-...'])
+    def test__get_device_link_symlink_found_after_retry(self, mock_listdir,
+                                                        mock_realpath,
+                                                        mock_time):
+        # Return the expected realpath on the third retry
+        mock_realpath.side_effect = [
+            None, None, None, None, None, None, '/dev/sda']
+
+        # Assert that VolumeDeviceNotFound isn't raised
+        self.connector._get_device_link('wwn', '/dev/sda', None)
+
+        # Assert that listdir and realpath have been called correctly
+        mock_listdir.assert_has_calls(2 * [mock.call('/dev/disk/by-id/')])
+        self.assertEqual(2, mock_listdir.call_count)
+        mock_realpath.assert_has_calls(
+            2 * [mock.call('/dev/disk/by-id/scsi-wwn'),
+                 mock.call('/dev/disk/by-id/dm-...'),
+                 mock.call('/dev/disk/by-id/scsi-...')]
+            + [mock.call('/dev/disk/by-id/scsi-wwn')])
+        self.assertEqual(7, mock_realpath.call_count)
+
+    @mock.patch('time.sleep')
+    @mock.patch('os.path.realpath')
+    @mock.patch('os.listdir', return_value=['dm-...', 'scsi-...'])
+    def test__get_device_link_symlink_found_after_retry_by_listdir(
+            self, mock_listdir, mock_realpath, mock_time):
+
+        # Return the expected realpath on the second retry while looping over
+        # the devices returned by listdir
+        mock_realpath.side_effect = [
+            None, None, None, None, None, '/dev/sda']
+
+        # Assert that VolumeDeviceNotFound isn't raised
+        self.connector._get_device_link('wwn', '/dev/sda', None)
+
+        # Assert that listdir and realpath have been called correctly
+        mock_listdir.assert_has_calls(2 * [mock.call('/dev/disk/by-id/')])
+        self.assertEqual(2, mock_listdir.call_count)
+        mock_realpath.assert_has_calls(
+            2 * [mock.call('/dev/disk/by-id/scsi-wwn'),
+                 mock.call('/dev/disk/by-id/dm-...'),
+                 mock.call('/dev/disk/by-id/scsi-...')])
+        self.assertEqual(6, mock_realpath.call_count)
 
     @mock.patch.object(iscsi.ISCSIConnector, '_run_iscsiadm_bare')
     def test_get_node_startup_values(self, run_iscsiadm_bare_mock):