namespace.c

	seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
	err = show_sb_opts(m, mnt->mnt_sb);
	if (err)
		goto out;
	show_mnt_opts(m, mnt);
	if (mnt->mnt_sb->s_op->show_options)
		err = mnt->mnt_sb->s_op->show_options(m, mnt);
	seq_puts(m, " 0 0\n");
out:
	return err;
}

const struct seq_operations mounts_op = {
	.start	= m_start,
	.next	= m_next,
	.stop	= m_stop,
	.show	= show_vfsmnt
};

static int show_mountinfo(struct seq_file *m, void *v)
{
	struct proc_mounts *p = m->private;
	struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
	struct super_block *sb = mnt->mnt_sb;
	struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
	struct path root = p->root;
	int err = 0;

	seq_printf(m, "%i %i %u:%u ", mnt->mnt_id, mnt->mnt_parent->mnt_id,
		   MAJOR(sb->s_dev), MINOR(sb->s_dev));
	if (sb->s_op->show_path)
		err = sb->s_op->show_path(m, mnt);
	else
		seq_dentry(m, mnt->mnt_root, " \t\n\\");
	if (err)
		goto out;
	seq_putc(m, ' ');

	/* mountpoints outside of chroot jail will give SEQ_SKIP on this */
	err = seq_path_root(m, &mnt_path, &root, " \t\n\\");
	if (err)
		goto out;

	seq_puts(m, mnt->mnt_flags & MNT_READONLY ? " ro" : " rw");
	show_mnt_opts(m, mnt);

	/* Tagged fields ("foo:X" or "bar") */
	if (IS_MNT_SHARED(mnt))
		seq_printf(m, " shared:%i", mnt->mnt_group_id);
	if (IS_MNT_SLAVE(mnt)) {
		int master = mnt->mnt_master->mnt_group_id;
		int dom = get_dominating_id(mnt, &p->root);
		seq_printf(m, " master:%i", master);
		if (dom && dom != master)
			seq_printf(m, " propagate_from:%i", dom);
	}
	if (IS_MNT_UNBINDABLE(mnt))
		seq_puts(m, " unbindable");

	/* Filesystem specific data */
	seq_puts(m, " - ");
	show_type(m, sb);
	seq_putc(m, ' ');
	if (sb->s_op->show_devname)
		err = sb->s_op->show_devname(m, mnt);
	else
		mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
	if (err)
		goto out;
	seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
	err = show_sb_opts(m, sb);
	if (err)
		goto out;
	if (sb->s_op->show_options)
		err = sb->s_op->show_options(m, mnt);
	seq_putc(m, '\n');
out:
	return err;
}

const struct seq_operations mountinfo_op = {
	.start	= m_start,
	.next	= m_next,
	.stop	= m_stop,
	.show	= show_mountinfo,
};

static int show_vfsstat(struct seq_file *m, void *v)
{
	struct vfsmount *mnt = list_entry(v, struct vfsmount, mnt_list);
	struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt };
	int err = 0;

	/* device */
	if (mnt->mnt_sb->s_op->show_devname) {
		seq_puts(m, "device ");
		err = mnt->mnt_sb->s_op->show_devname(m, mnt);
	} else {
		if (mnt->mnt_devname) {
			seq_puts(m, "device ");
			mangle(m, mnt->mnt_devname);
		} else
			seq_puts(m, "no device");
	}

	/* mount point */
	seq_puts(m, " mounted on ");
	seq_path(m, &mnt_path, " \t\n\\");
	seq_putc(m, ' ');

	/* file system type */
	seq_puts(m, "with fstype ");
	show_type(m, mnt->mnt_sb);

	/* optional statistics */
	if (mnt->mnt_sb->s_op->show_stats) {
		seq_putc(m, ' ');
		if (!err)
			err = mnt->mnt_sb->s_op->show_stats(m, mnt);
	}

	seq_putc(m, '\n');
	return err;
}

const struct seq_operations mountstats_op = {
	.start	= m_start,
	.next	= m_next,
	.stop	= m_stop,
	.show	= show_vfsstat,
};
#endif  /* CONFIG_PROC_FS */

/**
 * may_umount_tree - check if a mount tree is busy
 * @mnt: root of mount tree
 *
 * This is called to check if a tree of mounts has any
 * open files, pwds, chroots or sub mounts that are
 * busy.
 */
int may_umount_tree(struct vfsmount *mnt)
{
	int actual_refs = 0;
	int minimum_refs = 0;
	struct mount *p;
	BUG_ON(!mnt);

	/* write lock needed for mnt_get_count */
	br_write_lock(vfsmount_lock);
	for (p = real_mount(mnt); p; p = next_mnt(p, mnt)) {
		actual_refs += mnt_get_count(&p->mnt);
		minimum_refs += 2;
	}
	br_write_unlock(vfsmount_lock);

	if (actual_refs > minimum_refs)
		return 0;

	return 1;
}

EXPORT_SYMBOL(may_umount_tree);

/**
 * may_umount - check if a mount point is busy
 * @mnt: root of mount
 *
 * This is called to check if a mount point has any
 * open files, pwds, chroots or sub mounts. If the
 * mount has sub mounts this will return busy
 * regardless of whether the sub mounts are busy.
 *
 * Doesn't take quota and stuff into account. IOW, in some cases it will
 * give false negatives. The main reason why it's here is that we need
 * a non-destructive way to look for easily umountable filesystems.
 */
int may_umount(struct vfsmount *mnt)
{
	int ret = 1;
	down_read(&namespace_sem);
	br_write_lock(vfsmount_lock);
	if (propagate_mount_busy(mnt, 2))
		ret = 0;
	br_write_unlock(vfsmount_lock);
	up_read(&namespace_sem);
	return ret;
}

EXPORT_SYMBOL(may_umount);

void release_mounts(struct list_head *head)
{
	struct mount *mnt;
	while (!list_empty(head)) {
		mnt = list_first_entry(head, struct mount, mnt_hash);
		list_del_init(&mnt->mnt_hash);
		if (mnt_has_parent(&mnt->mnt)) {
			struct dentry *dentry;
			struct vfsmount *m;

			br_write_lock(vfsmount_lock);
			dentry = mnt->mnt.mnt_mountpoint;
			m = mnt->mnt.mnt_parent;
			mnt->mnt.mnt_mountpoint = mnt->mnt.mnt_root;
			mnt->mnt.mnt_parent = &mnt->mnt;
			m->mnt_ghosts--;
			br_write_unlock(vfsmount_lock);
			dput(dentry);
			mntput(m);
		}
		mntput(&mnt->mnt);
	}
}

/*
 * vfsmount lock must be held for write
 * namespace_sem must be held for write
 */
void umount_tree(struct mount *mnt, int propagate, struct list_head *kill)
{
	LIST_HEAD(tmp_list);
	struct mount *p;

	for (p = mnt; p; p = next_mnt(p, &mnt->mnt))
		list_move(&p->mnt_hash, &tmp_list);

	if (propagate)
		propagate_umount(&tmp_list);

	list_for_each_entry(p, &tmp_list, mnt_hash) {
		list_del_init(&p->mnt.mnt_expire);
		list_del_init(&p->mnt.mnt_list);
		__touch_mnt_namespace(p->mnt.mnt_ns);
		p->mnt.mnt_ns = NULL;
		__mnt_make_shortterm(&p->mnt);
		list_del_init(&p->mnt.mnt_child);
		if (mnt_has_parent(&p->mnt)) {
			p->mnt.mnt_parent->mnt_ghosts++;
			dentry_reset_mounted(p->mnt.mnt_mountpoint);
		}
		change_mnt_propagation(p, MS_PRIVATE);
	}
	list_splice(&tmp_list, kill);
}

static void shrink_submounts(struct mount *mnt, struct list_head *umounts);

static int do_umount(struct vfsmount *mnt, int flags)
{
	struct super_block *sb = mnt->mnt_sb;
	int retval;
	LIST_HEAD(umount_list);

	retval = security_sb_umount(mnt, flags);
	if (retval)
		return retval;

	/*
	 * Allow userspace to request a mountpoint be expired rather than
	 * unmounting unconditionally. Unmount only happens if:
	 *  (1) the mark is already set (the mark is cleared by mntput())
	 *  (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
	 */
	if (flags & MNT_EXPIRE) {
		if (mnt == current->fs->root.mnt ||
		    flags & (MNT_FORCE | MNT_DETACH))
			return -EINVAL;

		/*
		 * probably don't strictly need the lock here if we examined
		 * all race cases, but it's a slowpath.
		 */
		br_write_lock(vfsmount_lock);
		if (mnt_get_count(mnt) != 2) {
			br_write_unlock(vfsmount_lock);
			return -EBUSY;
		}
		br_write_unlock(vfsmount_lock);

		if (!xchg(&mnt->mnt_expiry_mark, 1))
			return -EAGAIN;
	}

	/*
	 * If we may have to abort operations to get out of this
	 * mount, and they will themselves hold resources we must
	 * allow the fs to do things. In the Unix tradition of
	 * 'Gee thats tricky lets do it in userspace' the umount_begin
	 * might fail to complete on the first run through as other tasks
	 * must return, and the like. Thats for the mount program to worry
	 * about for the moment.
	 */

	if (flags & MNT_FORCE && sb->s_op->umount_begin) {
		sb->s_op->umount_begin(sb);
	}

	/*
	 * No sense to grab the lock for this test, but test itself looks
	 * somewhat bogus. Suggestions for better replacement?
	 * Ho-hum... In principle, we might treat that as umount + switch
	 * to rootfs. GC would eventually take care of the old vfsmount.
	 * Actually it makes sense, especially if rootfs would contain a
	 * /reboot - static binary that would close all descriptors and
	 * call reboot(9). Then init(8) could umount root and exec /reboot.
	 */
	if (mnt == current->fs->root.mnt && !(flags & MNT_DETACH)) {
		/*
		 * Special case for "unmounting" root ...
		 * we just try to remount it readonly.
		 */
		down_write(&sb->s_umount);
		if (!(sb->s_flags & MS_RDONLY))
			retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
		up_write(&sb->s_umount);
		return retval;
	}

	down_write(&namespace_sem);
	br_write_lock(vfsmount_lock);
	event++;

	if (!(flags & MNT_DETACH))
		shrink_submounts(real_mount(mnt), &umount_list);

	retval = -EBUSY;
	if (flags & MNT_DETACH || !propagate_mount_busy(mnt, 2)) {
		if (!list_empty(&mnt->mnt_list))
			umount_tree(real_mount(mnt), 1, &umount_list);
		retval = 0;
	}
	br_write_unlock(vfsmount_lock);
	up_write(&namespace_sem);
	release_mounts(&umount_list);
	return retval;
}

/*
 * Now umount can handle mount points as well as block devices.
 * This is important for filesystems which use unnamed block devices.
 *
 * We now support a flag for forced unmount like the other 'big iron'
 * unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
 */

SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
{
	struct path path;
	int retval;
	int lookup_flags = 0;

	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
		return -EINVAL;

	if (!(flags & UMOUNT_NOFOLLOW))
		lookup_flags |= LOOKUP_FOLLOW;

	retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
	if (retval)
		goto out;
	retval = -EINVAL;
	if (path.dentry != path.mnt->mnt_root)
		goto dput_and_out;
	if (!check_mnt(path.mnt))
		goto dput_and_out;

	retval = -EPERM;
	if (!capable(CAP_SYS_ADMIN))
		goto dput_and_out;

	retval = do_umount(path.mnt, flags);
dput_and_out:
	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
	dput(path.dentry);
	mntput_no_expire(path.mnt);
out:
	return retval;
}

#ifdef __ARCH_WANT_SYS_OLDUMOUNT

/*
 *	The 2.0 compatible umount. No flags.
 */
SYSCALL_DEFINE1(oldumount, char __user *, name)
{
	return sys_umount(name, 0);
}

#endif

static int mount_is_safe(struct path *path)
{
	if (capable(CAP_SYS_ADMIN))
		return 0;
	return -EPERM;
#ifdef notyet
	if (S_ISLNK(path->dentry->d_inode->i_mode))
		return -EPERM;
	if (path->dentry->d_inode->i_mode & S_ISVTX) {
		if (current_uid() != path->dentry->d_inode->i_uid)
			return -EPERM;
	}
	if (inode_permission(path->dentry->d_inode, MAY_WRITE))
		return -EPERM;
	return 0;
#endif
}

struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
					int flag)
{
	struct mount *res, *p, *q;
	struct vfsmount *r;
	struct path path;

	if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(&mnt->mnt))
		return NULL;

	res = q = clone_mnt(mnt, dentry, flag);
	if (!q)
		goto Enomem;
	q->mnt.mnt_mountpoint = mnt->mnt.mnt_mountpoint;

	p = mnt;
	list_for_each_entry(r, &mnt->mnt.mnt_mounts, mnt_child) {
		struct mount *s;
		if (!is_subdir(r->mnt_mountpoint, dentry))
			continue;

		for (s = real_mount(r); s; s = next_mnt(s, r)) {
			if (!(flag & CL_COPY_ALL) && IS_MNT_UNBINDABLE(&s->mnt)) {
				s = skip_mnt_tree(s);
				continue;
			}
			while (p != real_mount(s->mnt.mnt_parent)) {
				p = real_mount(p->mnt.mnt_parent);
				q = real_mount(q->mnt.mnt_parent);
			}
			p = s;
			path.mnt = &q->mnt;
			path.dentry = p->mnt.mnt_mountpoint;
			q = clone_mnt(p, p->mnt.mnt_root, flag);
			if (!q)
				goto Enomem;
			br_write_lock(vfsmount_lock);
			list_add_tail(&q->mnt.mnt_list, &res->mnt.mnt_list);
			attach_mnt(q, &path);
			br_write_unlock(vfsmount_lock);
		}
	}
	return res;
Enomem:
	if (res) {
		LIST_HEAD(umount_list);
		br_write_lock(vfsmount_lock);
		umount_tree(res, 0, &umount_list);
		br_write_unlock(vfsmount_lock);
		release_mounts(&umount_list);
	}
	return NULL;
}

struct vfsmount *collect_mounts(struct path *path)
{
	struct mount *tree;
	down_write(&namespace_sem);
	tree = copy_tree(real_mount(path->mnt), path->dentry,
			 CL_COPY_ALL | CL_PRIVATE);
	up_write(&namespace_sem);
	return tree ? &tree->mnt : NULL;
}

void drop_collected_mounts(struct vfsmount *mnt)
{
	LIST_HEAD(umount_list);
	down_write(&namespace_sem);
	br_write_lock(vfsmount_lock);
	umount_tree(real_mount(mnt), 0, &umount_list);
	br_write_unlock(vfsmount_lock);
	up_write(&namespace_sem);
	release_mounts(&umount_list);
}

int iterate_mounts(int (*f)(struct vfsmount *, void *), void *arg,
		   struct vfsmount *root)
{
	struct vfsmount *mnt;
	int res = f(root, arg);
	if (res)
		return res;
	list_for_each_entry(mnt, &root->mnt_list, mnt_list) {
		res = f(mnt, arg);
		if (res)
			return res;
	}
	return 0;
}

static void cleanup_group_ids(struct mount *mnt, struct mount *end)
{
	struct mount *p;

	for (p = mnt; p != end; p = next_mnt(p, &mnt->mnt)) {
		if (p->mnt.mnt_group_id && !IS_MNT_SHARED(&p->mnt))
			mnt_release_group_id(p);
	}
}

static int invent_group_ids(struct mount *mnt, bool recurse)
{
	struct mount *p;

	for (p = mnt; p; p = recurse ? next_mnt(p, &mnt->mnt) : NULL) {
		if (!p->mnt.mnt_group_id && !IS_MNT_SHARED(&p->mnt)) {
			int err = mnt_alloc_group_id(p);
			if (err) {
				cleanup_group_ids(mnt, p);
				return err;
			}
		}
	}

	return 0;
}

/*
 *  @source_mnt : mount tree to be attached
 *  @nd         : place the mount tree @source_mnt is attached
 *  @parent_nd  : if non-null, detach the source_mnt from its parent and
 *  		   store the parent mount and mountpoint dentry.
 *  		   (done when source_mnt is moved)
 *
 *  NOTE: in the table below explains the semantics when a source mount
 *  of a given type is attached to a destination mount of a given type.
 * ---------------------------------------------------------------------------
 * |         BIND MOUNT OPERATION                                            |
 * |**************************************************************************
 * | source-->| shared        |       private  |       slave    | unbindable |
 * | dest     |               |                |                |            |
 * |   |      |               |                |                |            |
 * |   v      |               |                |                |            |
 * |**************************************************************************
 * |  shared  | shared (++)   |     shared (+) |     shared(+++)|  invalid   |
 * |          |               |                |                |            |
 * |non-shared| shared (+)    |      private   |      slave (*) |  invalid   |
 * ***************************************************************************
 * A bind operation clones the source mount and mounts the clone on the
 * destination mount.
 *
 * (++)  the cloned mount is propagated to all the mounts in the propagation
 * 	 tree of the destination mount and the cloned mount is added to
 * 	 the peer group of the source mount.
 * (+)   the cloned mount is created under the destination mount and is marked
 *       as shared. The cloned mount is added to the peer group of the source
 *       mount.
 * (+++) the mount is propagated to all the mounts in the propagation tree
 *       of the destination mount and the cloned mount is made slave
 *       of the same master as that of the source mount. The cloned mount
 *       is marked as 'shared and slave'.
 * (*)   the cloned mount is made a slave of the same master as that of the
 * 	 source mount.
 *
 * ---------------------------------------------------------------------------
 * |         		MOVE MOUNT OPERATION                                 |
 * |**************************************************************************
 * | source-->| shared        |       private  |       slave    | unbindable |
 * | dest     |               |                |                |            |
 * |   |      |               |                |                |            |
 * |   v      |               |                |                |            |
 * |**************************************************************************
 * |  shared  | shared (+)    |     shared (+) |    shared(+++) |  invalid   |
 * |          |               |                |                |            |
 * |non-shared| shared (+*)   |      private   |    slave (*)   | unbindable |
 * ***************************************************************************
 *
 * (+)  the mount is moved to the destination. And is then propagated to
 * 	all the mounts in the propagation tree of the destination mount.
 * (+*)  the mount is moved to the destination.
 * (+++)  the mount is moved to the destination and is then propagated to
 * 	all the mounts belonging to the destination mount's propagation tree.
 * 	the mount is marked as 'shared and slave'.
 * (*)	the mount continues to be a slave at the new location.
 *
 * if the source mount is a tree, the operations explained above is
 * applied to each mount in the tree.
 * Must be called without spinlocks held, since this function can sleep
 * in allocations.
 */
static int attach_recursive_mnt(struct mount *source_mnt,
			struct path *path, struct path *parent_path)
{
	LIST_HEAD(tree_list);
	struct vfsmount *dest_mnt = path->mnt;
	struct dentry *dest_dentry = path->dentry;
	struct mount *child, *p;
	int err;

	if (IS_MNT_SHARED(dest_mnt)) {
		err = invent_group_ids(source_mnt, true);
		if (err)
			goto out;
	}
	err = propagate_mnt(dest_mnt, dest_dentry, &source_mnt->mnt, &tree_list);
	if (err)
		goto out_cleanup_ids;

	br_write_lock(vfsmount_lock);

	if (IS_MNT_SHARED(dest_mnt)) {
		for (p = source_mnt; p; p = next_mnt(p, &source_mnt->mnt))
			set_mnt_shared(p);
	}
	if (parent_path) {
		detach_mnt(source_mnt, parent_path);
		attach_mnt(source_mnt, path);
		touch_mnt_namespace(parent_path->mnt->mnt_ns);
	} else {
		mnt_set_mountpoint(dest_mnt, dest_dentry, &source_mnt->mnt);
		commit_tree(source_mnt);
	}

	list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
		list_del_init(&child->mnt_hash);
		commit_tree(child);
	}
	br_write_unlock(vfsmount_lock);

	return 0;

 out_cleanup_ids:
	if (IS_MNT_SHARED(dest_mnt))
		cleanup_group_ids(source_mnt, NULL);
 out:
	return err;
}

static int lock_mount(struct path *path)
{
	struct vfsmount *mnt;
retry:
	mutex_lock(&path->dentry->d_inode->i_mutex);
	if (unlikely(cant_mount(path->dentry))) {
		mutex_unlock(&path->dentry->d_inode->i_mutex);
		return -ENOENT;
	}
	down_write(&namespace_sem);
	mnt = lookup_mnt(path);
	if (likely(!mnt))
		return 0;
	up_write(&namespace_sem);
	mutex_unlock(&path->dentry->d_inode->i_mutex);
	path_put(path);
	path->mnt = mnt;
	path->dentry = dget(mnt->mnt_root);
	goto retry;
}

static void unlock_mount(struct path *path)
{
	up_write(&namespace_sem);
	mutex_unlock(&path->dentry->d_inode->i_mutex);
}

static int graft_tree(struct vfsmount *mnt, struct path *path)
{
	if (mnt->mnt_sb->s_flags & MS_NOUSER)
		return -EINVAL;

	if (S_ISDIR(path->dentry->d_inode->i_mode) !=
	      S_ISDIR(mnt->mnt_root->d_inode->i_mode))
		return -ENOTDIR;

	if (d_unlinked(path->dentry))
		return -ENOENT;

	return attach_recursive_mnt(real_mount(mnt), path, NULL);
}

/*
 * Sanity check the flags to change_mnt_propagation.
 */

static int flags_to_propagation_type(int flags)
{
	int type = flags & ~(MS_REC | MS_SILENT);

	/* Fail if any non-propagation flags are set */
	if (type & ~(MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
		return 0;
	/* Only one propagation flag should be set */
	if (!is_power_of_2(type))
		return 0;
	return type;
}

/*
 * recursively change the type of the mountpoint.
 */
static int do_change_type(struct path *path, int flag)
{
	struct mount *m;
	struct mount *mnt = real_mount(path->mnt);
	int recurse = flag & MS_REC;
	int type;
	int err = 0;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	if (path->dentry != path->mnt->mnt_root)
		return -EINVAL;

	type = flags_to_propagation_type(flag);
	if (!type)
		return -EINVAL;

	down_write(&namespace_sem);
	if (type == MS_SHARED) {
		err = invent_group_ids(mnt, recurse);
		if (err)
			goto out_unlock;
	}

	br_write_lock(vfsmount_lock);
	for (m = mnt; m; m = (recurse ? next_mnt(m, &mnt->mnt) : NULL))
		change_mnt_propagation(m, type);
	br_write_unlock(vfsmount_lock);

 out_unlock:
	up_write(&namespace_sem);
	return err;
}

/*
 * do loopback mount.
 */
static int do_loopback(struct path *path, char *old_name,
				int recurse)
{
	LIST_HEAD(umount_list);
	struct path old_path;
	struct mount *mnt = NULL, *old;
	int err = mount_is_safe(path);
	if (err)
		return err;
	if (!old_name || !*old_name)
		return -EINVAL;
	err = kern_path(old_name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &old_path);
	if (err)
		return err;

	err = lock_mount(path);
	if (err)
		goto out;

	old = real_mount(old_path.mnt);

	err = -EINVAL;
	if (IS_MNT_UNBINDABLE(old_path.mnt))
		goto out2;

	if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt))
		goto out2;

	err = -ENOMEM;
	if (recurse)
		mnt = copy_tree(old, old_path.dentry, 0);
	else
		mnt = clone_mnt(old, old_path.dentry, 0);

	if (!mnt)
		goto out2;

	err = graft_tree(&mnt->mnt, path);
	if (err) {
		br_write_lock(vfsmount_lock);
		umount_tree(mnt, 0, &umount_list);
		br_write_unlock(vfsmount_lock);
	}
out2:
	unlock_mount(path);
	release_mounts(&umount_list);
out:
	path_put(&old_path);
	return err;
}

static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
{
	int error = 0;
	int readonly_request = 0;

	if (ms_flags & MS_RDONLY)
		readonly_request = 1;
	if (readonly_request == __mnt_is_readonly(mnt))
		return 0;

	if (readonly_request)
		error = mnt_make_readonly(mnt);
	else
		__mnt_unmake_readonly(mnt);
	return error;
}

/*
 * change filesystem flags. dir should be a physical root of filesystem.
 * If you've mounted a non-root directory somewhere and want to do remount
 * on it - tough luck.
 */
static int do_remount(struct path *path, int flags, int mnt_flags,
		      void *data)
{
	int err;
	struct super_block *sb = path->mnt->mnt_sb;

	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;

	if (!check_mnt(path->mnt))
		return -EINVAL;

	if (path->dentry != path->mnt->mnt_root)
		return -EINVAL;

	err = security_sb_remount(sb, data);
	if (err)
		return err;

	down_write(&sb->s_umount);
	if (flags & MS_BIND)
		err = change_mount_flags(path->mnt, flags);
	else
		err = do_remount_sb(sb, flags, data, 0);
	if (!err) {
		br_write_lock(vfsmount_lock);
		mnt_flags |= path->mnt->mnt_flags & MNT_PROPAGATION_MASK;
		path->mnt->mnt_flags = mnt_flags;
		br_write_unlock(vfsmount_lock);
	}
	up_write(&sb->s_umount);
	if (!err) {
		br_write_lock(vfsmount_lock);
		touch_mnt_namespace(path->mnt->mnt_ns);
		br_write_unlock(vfsmount_lock);
	}
	return err;
}

static inline int tree_contains_unbindable(struct mount *mnt)
{
	struct mount *p;
	for (p = mnt; p; p = next_mnt(p, &mnt->mnt)) {
		if (IS_MNT_UNBINDABLE(&p->mnt))
			return 1;
	}
	return 0;
}

static int do_move_mount(struct path *path, char *old_name)
{
	struct path old_path, parent_path;
	struct vfsmount *p;
	struct mount *old;
	int err = 0;
	if (!capable(CAP_SYS_ADMIN))
		return -EPERM;
	if (!old_name || !*old_name)
		return -EINVAL;
	err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);
	if (err)
		return err;

	err = lock_mount(path);
	if (err < 0)
		goto out;

	err = -EINVAL;
	if (!check_mnt(path->mnt) || !check_mnt(old_path.mnt))
		goto out1;

	if (d_unlinked(path->dentry))
		goto out1;

	err = -EINVAL;
	if (old_path.dentry != old_path.mnt->mnt_root)
		goto out1;

	old = real_mount(old_path.mnt);

	if (!mnt_has_parent(old_path.mnt))
		goto out1;

	if (S_ISDIR(path->dentry->d_inode->i_mode) !=
	      S_ISDIR(old_path.dentry->d_inode->i_mode))
		goto out1;
	/*
	 * Don't move a mount residing in a shared parent.
	 */
	if (IS_MNT_SHARED(old_path.mnt->mnt_parent))
		goto out1;
	/*
	 * Don't move a mount tree containing unbindable mounts to a destination
	 * mount which is shared.
	 */
	if (IS_MNT_SHARED(path->mnt) &&
	    tree_contains_unbindable(old))
		goto out1;
	err = -ELOOP;
	for (p = path->mnt; mnt_has_parent(p); p = p->mnt_parent)
		if (p == old_path.mnt)
			goto out1;

	err = attach_recursive_mnt(old, path, &parent_path);
	if (err)
		goto out1;

	/* if the mount is moved, it should no longer be expire
	 * automatically */
	list_del_init(&old_path.mnt->mnt_expire);
out1:
	unlock_mount(path);
out:
	if (!err)
		path_put(&parent_path);
	path_put(&old_path);
	return err;
}

static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype)
{
	int err;
	const char *subtype = strchr(fstype, '.');
	if (subtype) {
		subtype++;
		err = -EINVAL;
		if (!subtype[0])
			goto err;
	} else
		subtype = "";

	mnt->mnt_sb->s_subtype = kstrdup(subtype, GFP_KERNEL);
	err = -ENOMEM;
	if (!mnt->mnt_sb->s_subtype)
		goto err;
	return mnt;

 err:
	mntput(mnt);
	return ERR_PTR(err);
}

static struct vfsmount *
do_kern_mount(const char *fstype, int flags, const char *name, void *data)
{
	struct file_system_type *type = get_fs_type(fstype);
	struct vfsmount *mnt;
	if (!type)
		return ERR_PTR(-ENODEV);
	mnt = vfs_kern_mount(type, flags, name, data);
	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&
	    !mnt->mnt_sb->s_subtype)
		mnt = fs_set_subtype(mnt, fstype);
	put_filesystem(type);
	return mnt;
}

/*
 * add a mount into a namespace's mount tree
 */
static int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags)
{
	int err;

	mnt_flags &= ~(MNT_SHARED | MNT_WRITE_HOLD | MNT_INTERNAL);

	err = lock_mount(path);
	if (err)
		return err;

	err = -EINVAL;
	if (!(mnt_flags & MNT_SHRINKABLE) && !check_mnt(path->mnt))
		goto unlock;

	/* Refuse the same filesystem on the same mount point */
	err = -EBUSY;
	if (path->mnt->mnt_sb == newmnt->mnt_sb &&
	    path->mnt->mnt_root == path->dentry)
		goto unlock;

	err = -EINVAL;
	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
		goto unlock;

	newmnt->mnt_flags = mnt_flags;
	err = graft_tree(newmnt, path);

unlock:
	unlock_mount(path);