[PATCH] unbindable mounts

An unbindable mount does not forward or receive propagation.  Also
unbindable mount disallows bind mounts.  The semantics is as follows.

Bind semantics:
  It is invalid to bind mount an unbindable mount.

Move semantics:
  It is invalid to move an unbindable mount under shared mount.

Clone-namespace semantics:
  If a mount is unbindable in the parent namespace, the corresponding
  cloned mount in the child namespace becomes unbindable too.  Note:
  there is subtle difference, unbindable mounts cannot be bind mounted
  but can be cloned during clone-namespace.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index eef66f54c017..1b5f502a4b8f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -104,6 +104,7 @@ extern int dir_notify_enable;
 #define MS_MOVE         8192
 #define MS_REC          16384
 #define MS_VERBOSE      32768
+#define MS_UNBINDABLE   (1<<17) /* change to unbindable */
 #define MS_PRIVATE      (1<<18) /* change to private */
 #define MS_SLAVE        (1<<19) /* change to slave */
 #define MS_SHARED       (1<<20) /* change to shared */