From: Jan Blunck <j.blunck@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> Signed-off-by: Bharata B Rao <bharata@xxxxxxxxxxxxxxxxxx> --- fs/namespace.c | 13 ++++++++++++- include/linux/fs.h | 2 ++ include/linux/mount.h | 1 + 3 files changed, 15 insertions(+), 1 deletion(-) --- a/fs/namespace.c +++ b/fs/namespace.c @@ -376,6 +376,7 @@ static int show_vfsmnt(struct seq_file * { MNT_NOATIME, ",noatime" }, { MNT_NODIRATIME, ",nodiratime" }, { MNT_RELATIME, ",relatime" }, + { MNT_UNION, ",union" }, { 0, NULL } }; struct proc_fs_info *fs_infop; @@ -1127,6 +1128,14 @@ 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; + newmnt->mnt_flags = mnt_flags; if ((err = graft_tree(newmnt, nd))) goto unlock; @@ -1430,9 +1439,11 @@ long do_mount(char *dev_name, char *dir_ mnt_flags |= MNT_NODIRATIME; if (flags & MS_RELATIME) mnt_flags |= MNT_RELATIME; + if (flags & MS_UNION) + mnt_flags |= MNT_UNION; flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE | - MS_NOATIME | MS_NODIRATIME | MS_RELATIME); + MS_NOATIME | MS_NODIRATIME | MS_RELATIME | MS_UNION); /* ... and get the mountpoint */ retval = path_lookup(dir_name, LOOKUP_FOLLOW, &nd); --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -93,6 +93,7 @@ extern int dir_notify_enable; #define FS_REQUIRES_DEV 1 #define FS_BINARY_MOUNTDATA 2 #define FS_HAS_SUBTYPE 4 +#define FS_WHT 8 #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. @@ -109,6 +110,7 @@ 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 @@ -34,6 +34,7 @@ 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; - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html