Address comments

util/tarlayerformat.py

@@ -39,6 +39,9 @@ class TarLayerFormat(object):
 
         # Yield the tar header.
         if self.path_prefix:
+          # Note: We use a copy here because we need to make sure we copy over all the internal
+          # data of the tar header. We cannot use frombuf(tobuf()), however, because it doesn't
+          # properly handle large filenames.
           clone = copy.deepcopy(tar_info)
           clone.name = os.path.join(self.path_prefix, clone.name)
           yield clone.tobuf()