[RFC][PATCH 2/14] Add a new mount flag (MNT_UNION) for union mount

Bharata B Rao
2007-05-14T09:31:47Z

From: Jan Blunck <j.blunck@tu-harburg.de>
Subject: Add a new mount flag (MNT_UNION) for union mount.

Introduce MNT_UNION, MS_UNION and FS_WHT flags. There are the necessary flags
for doing

mount /dev/hda3 /mnt -o union

You need additional patches for util-linux for that to work.

Signed-off-by: Jan Blunck <j.blunck@tu-harburg.de>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
---
fs/namespace.c | 14 +++++++++++++-
include/linux/fs.h | 2 ++
include/linux/mount.h | 1 +
3 files changed, 16 insertions(+), 1 deletion(-)

--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -442,6 +442,7 @@ 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;
@@ -1256,6 +1257,14 @@ int do_add_mount(struct vfsmount *newmnt
if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
goto unlock;

+ /* Unions couldn't be writable if the filesystem
+ * doesn't know about whiteouts */
+ err = -ENOTSUPP;
+ if ((mnt_flags & MNT_UNION) &&
+ !(newmnt->mnt_sb->s_flags & MS_RDONLY) &&
+ !(newmnt->mnt_sb->s_type->fs_flags & FS_WHT))
+ goto unlock;
+
/* some flags may have been set earlier */
newmnt->mnt_flags |= mnt_flags;
if ((err = graft_tree(newmnt, nd)))
@@ -1562,9 +1571,12 @@ 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
@@ -97,6 +97,7 @@ extern int dir_notify_enable;
#define FS_BINARY_MOUNTDATA 2
#define FS_HAS_SUBTYPE 4
#define FS_SAFE 8 /* Safe to mount by unprivileged users */
+#define FS_WHT 16
#define FS_REVAL_DOT 16384 /* Check the paths ".", ".." for staleness */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move()
* during rename() internally.
@@ -113,6 +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 /* Union mount */
#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 /* propogation flag mask */
+#define MNT_UNION 0x4000 /* if the vfsmount is a union mount */

struct vfsmount {
struct list_head mnt_hash;