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>

diff --git a/fs/namespace.c b/fs/namespace.c
index 25c1dcf..d25d460 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1538,7 +1538,7 @@ static int do_remount(struct path *path, int flags, int mnt_flags,
                err = do_remount_sb(sb, flags, data, 0);
        if (!err) {
                spin_lock(&vfsmount_lock);
-               mnt_flags |= path->mnt->mnt_flags & MNT_PNODE_MASK;
+               mnt_flags |= path->mnt->mnt_flags & MNT_PROPAGATION_MASK;
                path->mnt->mnt_flags = mnt_flags;
                spin_unlock(&vfsmount_lock);
        }

diff --git a/fs/pnode.h b/fs/pnode.h
index 6c7ef32..1ea4ae1 100644 (file)
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -25,7 +25,7 @@
 
 static inline void set_mnt_shared(struct vfsmount *mnt)
 {
-       mnt->mnt_flags &= ~MNT_PNODE_MASK;
+       mnt->mnt_flags &= ~MNT_SHARED_MASK;
        mnt->mnt_flags |= MNT_SHARED;
 }
 

diff --git a/include/linux/mount.h b/include/linux/mount.h
index 5d52753..375d43a 100644 (file)
--- 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;