@@ -862,6 +862,7 @@ static void show_mnt_opts(struct seq_file *m, struct vfsmount *mnt)
 		{ MNT_NOATIME, ",noatime" },
 		{ MNT_NODIRATIME, ",nodiratime" },
 		{ MNT_RELATIME, ",relatime" },
+		{ MNT_UNION, ",union" },
 		{ 0, NULL }
 	};
 	const struct proc_fs_info *fs_infop;

@@ -2095,10 +2096,12 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
 		mnt_flags &= ~(MNT_RELATIME | MNT_NOATIME);
 	if (flags & MS_RDONLY)
 		mnt_flags |= MNT_READONLY;
+	if (flags & MS_UNION)
+		mnt_flags |= MNT_UNION;
 
 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | MS_BORN |
 		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT |
-		   MS_STRICTATIME);
+		   MS_STRICTATIME | MS_UNION);
 
 	if (flags & MS_REMOUNT)
 		retval = do_remount(&path, flags & ~MS_REMOUNT, mnt_flags,

@@ -191,6 +191,7 @@ struct inodes_stat_t {
 #define MS_REMOUNT	32	/* Alter flags of a mounted FS */
 #define MS_MANDLOCK	64	/* Allow mandatory locks on an FS */
 #define MS_DIRSYNC	128	/* Directory modifications are synchronous */
+#define MS_UNION	256	/* Merge namespace with FS mounted below */
 #define MS_NOATIME	1024	/* Do not update access times. */
 #define MS_NODIRATIME	2048	/* Do not update directory access times */
 #define MS_BIND		4096

@@ -46,6 +46,7 @@ struct mnt_namespace;
 
 #define MNT_INTERNAL	0x4000
 #define MNT_HARD_READONLY	0x8000	/* has a hard read-only ref on the sb */
+#define MNT_UNION	0x10000		/* top layer of a union mount */
 
 struct vfsmount {
 	struct list_head mnt_hash;