extern int mnt_want_write(struct vfsmount *mnt);
extern int mnt_want_write_file(struct file *file);
-extern int mnt_clone_write(struct vfsmount *mnt);
extern void mnt_drop_write(struct vfsmount *mnt);
extern void mnt_drop_write_file(struct file *file);
extern void mntput(struct vfsmount *mnt);