+# Metadata is stored in a file named .bupm in each directory. The
+# first metadata entry will be the metadata for the current directory.
+# The remaining entries will be for each of the other directory
+# elements, in the order they're listed in the index.
+#
+# Since the git tree elements are sorted according to
+# git.shalist_item_sort_key, the metalist items are accumulated as
+# (sort_key, metadata) tuples, and then sorted when the .bupm file is
+# created. The sort_key should have been computed using the element's
+# mangled name and git mode (after hashsplitting), but the code isn't
+# actually doing that but rather uses the element's real name and mode.
+# This makes things a bit more difficult when reading it back, see
+# vfs.ordered_tree_entries().
+
+# Maintain a stack of information representing the current location in
+# the archive being constructed. The current path is recorded in
+# parts, which will be something like ['', 'home', 'someuser'], and
+# the accumulated content and metadata for of the dirs in parts is
+# stored in parallel stacks in shalists and metalists.
+
+parts = [] # Current archive position (stack of dir names).
+shalists = [] # Hashes for each dir in paths.
+metalists = [] # Metadata for each dir in paths.
+
+
+def _push(part, metadata):
+ # Enter a new archive directory -- make it the current directory.