[RFC 15/26] union-mount: Add union-mount mount flag

[Jan Blunck]

Introduce MNT_UNION and MS_UNION flags. You need additional patches for
util-linux for that to work.

Signed-off-by: Jan Blunck <jblunck@xxxxxxx>
---
 fs/namespace.c        |    6 +++++-
 include/linux/fs.h    |    1 +
 include/linux/mount.h |    1 +
 3 files changed, 7 insertions(+), 1 deletion(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -437,6 +437,7 @@ static int show_vfsmnt(struct seq_file *
 		{ MNT_NODIRATIME, ",nodiratime" },
 		{ MNT_RELATIME, ",relatime" },
 		{ MNT_NOMNT, ",nomnt" },
+		{ MNT_UNION, ",union" },
 		{ 0, NULL }
 	};
 	struct proc_fs_info *fs_infop;
@@ -1558,9 +1559,12 @@ long do_mount(char *dev_name, char *dir_
 		mnt_flags |= MNT_RELATIME;
 	if (flags & MS_NOMNT)
 		mnt_flags |= MNT_NOMNT;
+	if (flags & MS_UNION)
+		mnt_flags |= MNT_UNION;
 
 	flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
-		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_NOMNT);
+		   MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_NOMNT |
+		   MS_UNION );
 
 	/* ... and get the mountpoint */
 	retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd);
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -114,6 +114,7 @@ extern int dir_notify_enable;
 #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
 #define MS_NOATIME	1024	/* Do not update access times. */
 #define MS_NODIRATIME	2048	/* Do not update directory access times */
 #define MS_BIND		4096
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -36,6 +36,7 @@ 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 */
+#define MNT_UNION	0x4000	/* if the vfsmount is a union mount */
 
 struct vfsmount {
 	struct list_head mnt_hash;

-- 

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