[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>

2 files changed, 2 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 */
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 7e133ae2a94f..dd4e83eba933 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -21,6 +21,7 @@
 #define MNT_NODEV       0x02
 #define MNT_NOEXEC      0x04
 #define MNT_SHARED      0x10    /* if the vfsmount is a shared mount */
+#define MNT_UNBINDABLE  0x20    /* if the vfsmount is a unbindable mount */
 #define MNT_PNODE_MASK  0x30    /* propogation flag mask */
 
 struct vfsmount {