Implement update_acl_on_path()

This allows to update or extend the existing ACL on path.

Signed-off-by: Georg Pfuetzenreuter <mail@georg-pfuetzenreuter.net>

pyacl/acl.py

@@ -248,18 +248,22 @@ def update_acl_on_path(new_acl, path):
   Example usage: update_acl_on_path(posix1e.ACL, '/etc/foo.txt')
   Return: None
   """
-  existing_acl = read_acl_from_path(path)
+  acl = read_acl_from_path(path)
   for entry in new_acl:
     tag_type = entry.tag_type
+
+    # keep existing entries which may only exist once
     if tag_type not in [ACL_USER_OBJ, ACL_GROUP_OBJ, ACL_OTHER, ACL_MASK]:
+
+      # replace existing user/group entries with new ones if the uid/gid matches
       if tag_type in [ACL_USER, ACL_GROUP]:
-        for existing_entry in existing_acl:
+        for existing_entry in acl:
           if tag_type == existing_entry.tag_type:
             if entry.qualifier == existing_entry.qualifier:
-              existing_acl.delete_entry(existing_entry)
-      existing_acl.append(entry)
+              acl.delete_entry(existing_entry)
+
+      acl.append(entry)
 
-  acl = existing_acl
   return apply_acl_to_path(acl, path)