Rename ImageCacheManager._list_base_images to _scan_base_images

The method's return value is never used, only its side-effects are
used. We rename it to reflect its actual usage, and remove the unused
return value to avoid confusion.

NOTE(mdbooth): The use of global state is a large part of what makes
ImageCacheManager hard to read. I don't mean to imply with this change
that's what should be done here, only to make it clearer to the reader
that it is what's being done currently.

Change-Id: Ic82f6d4f00fd1226673750538019339937a623bc

nova/tests/unit/virt/libvirt/test_imagecache.py

@@ -98,7 +98,7 @@ class ImageCacheManagerTestCase(test.NoDBTestCase):
         self.flags(instances_path='/var/lib/nova/instances')
 
         image_cache_manager = imagecache.ImageCacheManager()
-        image_cache_manager._list_base_images(base_dir)
+        image_cache_manager._scan_base_images(base_dir)
 
         sanitized = []
         for ent in image_cache_manager.unexplained_images:
@@ -256,7 +256,7 @@ class ImageCacheManagerTestCase(test.NoDBTestCase):
 
         base_dir = '/var/lib/nova/instances/_base'
         image_cache_manager = imagecache.ImageCacheManager()
-        image_cache_manager._list_base_images(base_dir)
+        image_cache_manager._scan_base_images(base_dir)
         res = list(image_cache_manager._find_base_file(base_dir, fingerprint))
 
         base_file = os.path.join(base_dir, fingerprint + '_10737418240')
@@ -276,7 +276,7 @@ class ImageCacheManagerTestCase(test.NoDBTestCase):
 
         base_dir = '/var/lib/nova/instances/_base'
         image_cache_manager = imagecache.ImageCacheManager()
-        image_cache_manager._list_base_images(base_dir)
+        image_cache_manager._scan_base_images(base_dir)
         res = list(image_cache_manager._find_base_file(base_dir, fingerprint))
 
         base_file1 = os.path.join(base_dir, fingerprint)

nova/tests/unit/virt/test_imagecache.py

@@ -63,9 +63,8 @@ class ImageCacheManagerTests(test.NoDBTestCase):
                           cache_manager.update, None, [])
         self.assertRaises(NotImplementedError,
                           cache_manager._get_base)
-        base_images = cache_manager._list_base_images(None)
-        self.assertEqual([], base_images['unexplained_images'])
-        self.assertEqual([], base_images['originals'])
+        self.assertRaises(NotImplementedError,
+                          cache_manager._scan_base_images, None)
         self.assertRaises(NotImplementedError,
                           cache_manager._age_and_verify_cached_images,
                           None, [], None)

nova/virt/imagecache.py

@@ -88,15 +88,11 @@ class ImageCacheManager(object):
                 'instance_names': instance_names,
                 'used_swap_images': used_swap_images}
 
-    def _list_base_images(self, base_dir):
-        """Return a list of the images present in _base.
-
-        This method returns a dictionary with the following keys:
-            - unexplained_images
-            - originals
+    def _scan_base_images(self, base_dir):
+        """Scan base images present in base_dir and populate internal
+        state.
         """
-        return {'unexplained_images': [],
-                'originals': []}
+        raise NotImplementedError()
 
     def _age_and_verify_cached_images(self, context, all_instances, base_dir):
         """Ages and verifies cached images."""

nova/virt/libvirt/imagecache.py

@@ -116,12 +116,10 @@ class ImageCacheManager(imagecache.ImageCacheManager):
                 LOG.debug('Adding %s into backend swap images', ent)
                 self.back_swap_images.add(ent)
 
-    def _list_base_images(self, base_dir):
-        """Return a list of the images present in _base.
-
-        Determine what images we have on disk. There will be other files in
-        this directory so we only grab the ones which are the right length
-        to be disk images.
+    def _scan_base_images(self, base_dir):
+        """Scan base images in base_dir and call _store_image or
+        _store_swap_image on each as appropriate. These methods populate
+        self.unexplained_images, self.originals, and self.back_swap_images.
         """
 
         digest_size = hashlib.sha1().digestsize * 2
@@ -157,9 +155,6 @@ class ImageCacheManager(imagecache.ImageCacheManager):
             else:
                 self._store_swap_image(ent)
 
-        return {'unexplained_images': self.unexplained_images,
-                'originals': self.originals}
-
     def _list_backing_images(self):
         """List the backing images currently in use."""
         inuse_images = []
@@ -452,7 +447,7 @@ class ImageCacheManager(imagecache.ImageCacheManager):
         # reset the local statistics
         self._reset_state()
         # read the cached images
-        self._list_base_images(base_dir)
+        self._scan_base_images(base_dir)
         # read running instances data
         running = self._list_running_instances(context, all_instances)
         self.used_images = running['used_images']