First few changes for the image diffs feature.

util/changes.py

@@ -0,0 +1,56 @@
+import marisa_trie
+import os
+
+
+AUFS_METADATA = u'.wh..wh.'
+
+AUFS_WHITEOUT = u'.wh.'
+AUFS_WHITEOUT_PREFIX_LENGTH = len(AUFS_WHITEOUT)
+
+
+def files_and_dirs(root_path, removed_prefix_collector):
+  for root, dirs, files in os.walk(unicode(root_path)):
+
+    rel_root = os.path.relpath(root, root_path)
+    yield rel_root
+
+    for one_file in files:
+      if one_file.startswith(AUFS_METADATA):
+        # Skip
+        continue
+
+      elif one_file.startswith(AUFS_WHITEOUT):
+        filename = one_file[AUFS_WHITEOUT_PREFIX_LENGTH:]
+        removed_prefix_collector.add(os.path.join(rel_root, filename))
+        continue
+
+      else:
+        yield os.path.join(rel_root, one_file)
+
+
+def compute_removed(base_trie, removed_prefixes):
+  for prefix in removed_prefixes:
+    for filename in base_trie.keys(prefix):
+      yield filename
+
+
+def compute_added_changed(base_trie, delta_trie):
+  added = set()
+  changed = set()
+
+  for filename in delta_trie.keys():
+    if filename not in base_trie:
+      added.add(filename)
+    else:
+      changed.add(filename)
+
+  return added, changed
+
+
+def new_fs(base_trie, added, removed):
+  for filename in base_trie.keys():
+    if filename not in removed:
+      yield filename
+
+  for filename in added:
+    yield filename