PowerMax Driver - Fix for legacy PowerMax OS around generations

In the previous version of PowerMax OS generations of snapVx were
used instead of unique snap ids which were just introduced.
A generation can be returned as a 0 integer which equates to False
in python.  The fix is to convert the int to a string if it is
returned from REST as an int.

Closes-Bug: #1938572
Change-Id: I5b660776190f3026296d6d3237bd3b0d609f769f

cinder/tests/unit/volume/drivers/dell_emc/powermax/test_powermax_rest.py

@@ -2431,3 +2431,25 @@ class PowerMaxRestTest(test.TestCase):
             exception.VolumeBackendAPIException,
             self.rest.get_ip_interface_physical_port,
             array_id, virtual_port, ip_address)
+
+    @mock.patch.object(rest.PowerMaxRest, 'get_volume_snaps',
+                       return_value=[{'snap_name': 'snap_name',
+                                      'snap_id': tpd.PowerMaxData.snap_id}])
+    def test_get_snap_id(self, mock_snaps):
+        snap_id = self.rest.get_snap_id(
+            self.data.array, self.data.device_id,
+            self.data.test_snapshot_snap_name)
+        self.assertEqual(self.data.snap_id, snap_id)
+
+    @mock.patch.object(rest.PowerMaxRest, 'get_volume_snaps',
+                       side_effect=[[{'snap_name': 'generation_int',
+                                      'generation': 0}],
+                                    [{'snap_name': 'generation_string',
+                                      'generation': '0'}]])
+    def test_get_snap_id_legacy_generation(self, mock_snaps):
+        self.rest.is_snap_id = False
+        for x in range(0, 2):
+            snap_id = self.rest.get_snap_id(
+                self.data.array, self.data.device_id,
+                self.data.test_snapshot_snap_name)
+            self.assertEqual('0', snap_id)

cinder/volume/drivers/dell_emc/powermax/rest.py

@@ -3397,7 +3397,7 @@ class PowerMaxRest(object):
                 message=exception_message)
         else:
             return snapshots[0].get('snap_id') if self.is_snap_id else (
-                snapshots[0].get('generation'))
+                self.utils.convert_to_string(snapshots[0].get('generation')))
 
     def get_major_minor_ucode(self, array):
         """Get the major and minor parts of the ucode

cinder/volume/drivers/dell_emc/powermax/utils.py

@@ -2086,3 +2086,12 @@ class PowerMaxUtils(object):
             service_level = str()
 
         return array_id, srp, service_level, workload
+
+    @staticmethod
+    def convert_to_string(in_value):
+        """Convert to string if value is an int
+
+        :param in_value: the input (most likely a str or int)
+        :returns: str
+        """
+        return in_value if isinstance(in_value, str) else str(in_value)

releasenotes/notes/powermax_legacy_generation_fix-09e437f955cd9d70.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    PowerMax driver `bug #1938572
+    <https://bugs.launchpad.net/cinder/+bug/1938572>`_ :
+    Legacy PowerMax OS fix to convert an int to a string if the generation
+    of snapVX is returned as an int from REST so that a 0  does not equate
+    to False in python.