VFS: Clean up shared mount flag propagation

The handling of mount flags in set_mnt_shared() got a little tangled
up during previous cleanups, with the following problems:

* MNT_PNODE_MASK is defined as a literal constant when it should be a
bitwise xor of other MNT_* flags
* set_mnt_shared() clears and then sets MNT_SHARED (part of MNT_PNODE_MASK)
* MNT_PNODE_MASK could use a comment in mount.h
* MNT_PNODE_MASK is a terrible name, change to MNT_SHARED_MASK

This patch fixes these problems.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 1 deletions

diff --git a/include/linux/mount.h b/include/linux/mount.h
index 5d5275364867..375d43a5d802 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -34,7 +34,16 @@ struct mnt_namespace;
 
 #define MNT_SHARED      0x1000  /* if the vfsmount is a shared mount */
 #define MNT_UNBINDABLE  0x2000  /* if the vfsmount is a unbindable mount */
-#define MNT_PNODE_MASK  0x3000  /* propagation flag mask */
+/*
+ * MNT_SHARED_MASK is the set of flags that should be cleared when a
+ * mount becomes shared.  Currently, this is only the flag that says a
+ * mount cannot be bind mounted, since this is how we create a mount
+ * that shares events with another mount.  If you add a new MNT_*
+ * flag, consider how it interacts with shared mounts.
+ */
+#define MNT_SHARED_MASK (MNT_UNBINDABLE)
+#define MNT_PROPAGATION_MASK    (MNT_SHARED | MNT_UNBINDABLE)
+
 
 struct vfsmount {
         struct list_head mnt_hash;