Smart save in SwiftSlotManager

Recent pypowervm changes alter the override spec of SlotMapStore such
that load(), save(), and delete() should no longer be overridden;
instead the subclass should override _load(key), _save(key, blob), and
_delete(key).  Although the original spec is still supported, using the
new spec confers advantages provided by SlotMapStore to invoke the
expensive _save operation only if something has changed in the slot
map.

Change-Id: I4ef03370bb84917851b11b256155c3c6218d9ada
Partial-Bug: 1584946

nova_powervm/tests/virt/powervm/test_slot.py

@@ -59,10 +59,7 @@ class TestSwiftSlotManager(test.TestCase):
                                               instance=self.inst)
 
     def test_load(self):
-        # Run load
-        self.slot_mgr.load()
-
-        # Validate the call
+        # load() should have been called internally by __init__
         self.store_api.fetch_slot_map.assert_called_with(
             self.inst.uuid + '_slot_map')
 
@@ -73,6 +70,16 @@ class TestSwiftSlotManager(test.TestCase):
         # Run save
         self.slot_mgr.save()
 
+        # Not called because nothing changed
+        self.store_api.store_slot_map.assert_not_called()
+
+        # Change something
+        mock_vfcmap = mock.Mock(server_adapter=mock.Mock(lpar_slot_num=123))
+        self.slot_mgr.register_vfc_mapping(mock_vfcmap, 'fabric')
+
+        # Run save
+        self.slot_mgr.save()
+
         # Validate the call
         self.store_api.store_slot_map.assert_called_once_with(
             self.inst.uuid + '_slot_map', mock.ANY)

nova_powervm/virt/powervm/slot.py

@@ -170,20 +170,19 @@ class SwiftSlotManager(NovaSlotManager):
         self.store_api = store_api
         super(SwiftSlotManager, self).__init__(**kwargs)
 
-    def load(self):
-        return self.store_api.fetch_slot_map(self.inst_key)
+    def _load(self, key):
+        return self.store_api.fetch_slot_map(key)
 
-    def save(self):
-        self.store_api.store_slot_map(self.inst_key, self.serialized)
+    def _save(self, key, blob):
+        self.store_api.store_slot_map(key, blob)
 
-    def delete(self):
+    def _delete(self, key):
         try:
-            self.store_api.delete_slot_map(self.inst_key)
+            self.store_api.delete_slot_map(key)
         except Exception:
             LOG.warning(_LW("Unable to delete the slot map from Swift backing "
-                            "store with ID %(inst_key)s.  Will require "
-                            "manual cleanup."), {'inst_key': self.inst_key},
-                        self.instance)
+                            "store with ID %(key)s.  Will require "
+                            "manual cleanup."), {'key': key}, self.instance)
 
 
 class NoopSlotManager(NovaSlotManager):