1. A method comprising: providing at a root node a virtual name space which has a first directory tree; providing at a file system on a leaf node a second directory tree, an access control information being set to a file system object of the second directory tree; mounting the second directory tree on a mount point of the first directory tree; specifying inheritable access control information set to a parent directory of the mount point; adding the specified inheritable access control information to the access control information set to the file system object of the second directory tree; unmounting the second directory tree from the mount point of the first directory tree; and selectively deleting the inheritable access control information from the access control information set to the file system object of the second directory tree.