struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
{
	struct mnt_namespace *ns;
	struct super_block *s;
	struct path path;
	int err;

	ns = create_mnt_ns(mnt);
	if (IS_ERR(ns))
		return ERR_CAST(ns);

	err = vfs_path_lookup(mnt->mnt_root, mnt,
			name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);

	put_mnt_ns(ns);

	if (err)
		return ERR_PTR(err);

	/* trade a vfsmount reference for active sb one */
	s = path.mnt->mnt_sb;
	atomic_inc(&s->s_active);
	mntput(path.mnt);
	/* lock the sucker */
	down_write(&s->s_umount);
	/* ... and return the root of (sub)tree on it */
	return path.dentry;
}
struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
{
	struct mnt_namespace *ns;
	struct super_block *s;
	struct path path;
	int err;

	ns = create_mnt_ns(mnt);
	if (IS_ERR(ns))
		return ERR_CAST(ns);

	err = vfs_path_lookup(mnt->mnt_root, mnt,
			name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);

	put_mnt_ns(ns);

	if (err)
		return ERR_PTR(err);

	 
	s = path.mnt->mnt_sb;
	atomic_inc(&s->s_active);
	mntput(path.mnt);
	 
	down_write(&s->s_umount);
	 
	return path.dentry;
}