tree bfe4f910e16663db585336bc7744fbbf312b4701
parent ceeb0e5d39fcdf4dca2c997bf225c7fc49200b37
author Eric W. Biederman <ebiederm@xmission.com> 1431204889 -0500
committer Eric W. Biederman <ebiederm@xmission.com> 1435764997 -0500

fs: Add helper functions for permanently empty directories.

To ensure it is safe to mount proc and sysfs I need to check if
filesystems that are mounted on top of them are mounted on truly empty
directories.  Given that some directories can gain entries over time,
knowing that a directory is empty right now is insufficient.

Therefore add supporting infrastructure for permantently empty
directories that proc and sysfs can use when they create mount points
for filesystems and fs_fully_visible can use to test for permanently
empty directories to ensure that nothing will be gained by mounting a
fresh copy of proc or sysfs.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>