Don't verify image hashes if checksumming is disabled.

There was a bug where we were checking base image checksums, even
if checksumming was disabled, if there was already a cached checksum
for the image. This resolves bug 1075017.

DocImpact

Change-Id: I38f5914cd9d6326fdf5e5d7f0f57885ff8b5ff32
(cherry picked from commit 1442177)

nova/tests/test_imagecache.py

@@ -379,6 +379,29 @@ def test_verify_checksum(self):
                 res = image_cache_manager._verify_checksum(img, fname)
                 self.assertTrue(res)
 
+    def test_verify_checksum_disabled(self):
+        img = {'container_format': 'ami', 'id': '42'}
+
+        self.flags(checksum_base_images=False)
+
+        with self._intercept_log_messages() as stream:
+            with utils.tempdir() as tmpdir:
+                self.flags(instances_path=tmpdir)
+                self.flags(image_info_filename_pattern=('$instances_path/'
+                                                        '%(image)s.info'))
+                fname, info_fname, testdata = self._make_checksum(tmpdir)
+
+                # Checksum is valid
+                f = open(info_fname, 'w')
+                csum = hashlib.sha1()
+                csum.update(testdata)
+                f.write('{"sha1": "%s"}\n' % csum.hexdigest())
+                f.close()
+
+                image_cache_manager = imagecache.ImageCacheManager()
+                res = image_cache_manager._verify_checksum(img, fname)
+                self.assertTrue(res is None)
+
     def test_verify_checksum_invalid_json(self):
         img = {'container_format': 'ami', 'id': '42'}
 
@@ -653,6 +676,7 @@ def test_handle_base_image_used_missing(self):
             self.assertEquals(image_cache_manager.corrupt_base_files, [])
 
     def test_handle_base_image_checksum_fails(self):
+        self.flags(checksum_base_images=True)
         self.stubs.Set(virtutils, 'chown', lambda x, y: None)
 
         img = '123'

nova/virt/libvirt/imagecache.py

@@ -226,6 +226,9 @@ def _verify_checksum(self, img_id, base_file, create_if_missing=True):
         handle manually when it occurs.
         """
 
+        if not FLAGS.checksum_base_images:
+            return None
+
         stored_checksum = read_stored_checksum(base_file)
         if stored_checksum:
             f = open(base_file, 'r')
@@ -251,7 +254,7 @@ def _verify_checksum(self, img_id, base_file, create_if_missing=True):
             # NOTE(mikal): If the checksum file is missing, then we should
             # create one. We don't create checksums when we download images
             # from glance because that would delay VM startup.
-            if FLAGS.checksum_base_images and create_if_missing:
+            if create_if_missing:
                 write_stored_checksum(base_file)
 
             return None