Fix extend operation of shrinked share in generic driver

If a share is shrank from 10G to 5G, the volume is still 10G.
This share`s size display is 5G, but the share extend newsize
must be > 10G in the old code. So, I think only need to perform
resize_filesystem when the share extend newsize <= volume size.
The volume extension is performed only when new size larger than
volume size.

Change-Id: I7e49b446445b8005e2eb23e1d439354eb24915e0
Close-Bug: #1639188

manila/share/drivers/generic.py

@@ -667,16 +667,18 @@ class GenericShareDriver(driver.ExecuteMixin, driver.ShareDriver):
         helper = self._get_helper(share)
         helper.disable_access_for_maintenance(server_details, share['name'])
         self._unmount_device(share, server_details)
-        self._detach_volume(self.admin_context, share, server_details)
-
         volume = self._get_volume(self.admin_context, share['id'])
-        volume = self._extend_volume(self.admin_context, volume, new_size)
 
-        volume = self._attach_volume(
-            self.admin_context,
-            share,
-            server_details['instance_id'],
-            volume)
+        if int(new_size) > volume['size']:
+            self._detach_volume(self.admin_context, share, server_details)
+            volume = self._extend_volume(self.admin_context, volume, new_size)
+
+            volume = self._attach_volume(
+                self.admin_context,
+                share,
+                server_details['instance_id'],
+                volume)
+
         self._resize_filesystem(server_details, volume)
         self._mount_device(share, server_details, volume)
         helper.restore_access_after_maintenance(server_details,

manila/tests/share/drivers/test_generic.py

@@ -1630,8 +1630,12 @@ class GenericShareDriverTestCase(test.TestCase):
             "fake", "fake"
         )
 
-    def test_extend_share(self):
-        fake_volume = "fake"
+    @ddt.data(100, 130, 123)
+    def test_extend_share(self, volume_size):
+        fake_volume = {
+            "name": "fake",
+            "size": volume_size,
+        }
         fake_share = {
             'id': 'fake',
             'share_proto': 'NFS',
@@ -1662,14 +1666,21 @@ class GenericShareDriverTestCase(test.TestCase):
             self._driver.service_instance_manager.get_common_server.called)
         self._driver._unmount_device.assert_called_once_with(
             fake_share, srv_details)
-        self._driver._detach_volume.assert_called_once_with(
-            mock.ANY, fake_share, srv_details)
         self._driver._get_volume.assert_called_once_with(
             mock.ANY, fake_share['id'])
-        self._driver._extend_volume.assert_called_once_with(
-            mock.ANY, fake_volume, new_size)
-        self._driver._attach_volume.assert_called_once_with(
-            mock.ANY, fake_share, srv_details['instance_id'], mock.ANY)
+
+        if new_size > volume_size:
+            self._driver._detach_volume.assert_called_once_with(
+                mock.ANY, fake_share, srv_details)
+            self._driver._extend_volume.assert_called_once_with(
+                mock.ANY, fake_volume, new_size)
+            self._driver._attach_volume.assert_called_once_with(
+                mock.ANY, fake_share, srv_details['instance_id'], mock.ANY)
+        else:
+            self.assertFalse(self._driver._detach_volume.called)
+            self.assertFalse(self._driver._extend_volume.called)
+            self.assertFalse(self._driver._attach_volume.called)
+
         self._helper_nfs.disable_access_for_maintenance.\
             assert_called_once_with(srv_details, 'test_share')
         self._helper_nfs.restore_access_after_maintenance.\

releasenotes/notes/bug-1639188-fix-extend-operation-of-shrinked-share-in-generic-driver-5c7f82faefaf26ea.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - In the Generic driver, the backing volume size is
+    greater than the share size when the share has been
+    shrunk. So share extend logic in this driver was
+    changed to only extend the backing volume if its
+    size is less than the size of the new, extended share.