/*
   *  linux/fs/pnode.c
   *
   * (C) Copyright IBM Corporation 2005.
   *	Released under GPL v2.
   *	Author : Ram Pai (linuxram@us.ibm.com)
   *
   */

  #include <linux/mnt_namespace.h>

  #include <linux/mount.h>
  #include <linux/fs.h>

  #include <linux/nsproxy.h>

  #include "internal.h"

  #include "pnode.h"

  /* return the next shared peer mount of @p */

  static inline struct mount *next_peer(struct mount *p)

  {

  	return list_entry(p->mnt_share.next, struct mount, mnt_share);

  }

  static inline struct mount *first_slave(struct mount *p)

  {

  	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);

  }

  static inline struct mount *next_slave(struct mount *p)

  {

  	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);

  }

  static struct mount *get_peer_under_root(struct mount *mnt,
  					 struct mnt_namespace *ns,
  					 const struct path *root)

  {

  	struct mount *m = mnt;

  
  	do {
  		/* Check the namespace first for optimization */

  		if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))

  			return m;

  		m = next_peer(m);

  	} while (m != mnt);

  
  	return NULL;
  }
  
  /*
   * Get ID of closest dominating peer group having a representative
   * under the given root.
   *
   * Caller must hold namespace_sem
   */

  int get_dominating_id(struct mount *mnt, const struct path *root)

  {

  	struct mount *m;

  	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {

  		struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);

  		if (d)

  			return d->mnt_group_id;

  	}
  
  	return 0;
  }

  static int do_make_slave(struct mount *mnt)

  {

  	struct mount *peer_mnt = mnt, *master = mnt->mnt_master;

  	struct mount *slave_mnt;

  
  	/*
  	 * slave 'mnt' to a peer mount that has the

  	 * same root dentry. If none is available then

  	 * slave it to anything that is available.
  	 */

  	while ((peer_mnt = next_peer(peer_mnt)) != mnt &&

  	       peer_mnt->mnt.mnt_root != mnt->mnt.mnt_root) ;

  
  	if (peer_mnt == mnt) {

  		peer_mnt = next_peer(mnt);

  		if (peer_mnt == mnt)
  			peer_mnt = NULL;
  	}

  	if (mnt->mnt_group_id && IS_MNT_SHARED(mnt) &&
  	    list_empty(&mnt->mnt_share))

  		mnt_release_group_id(mnt);

  	list_del_init(&mnt->mnt_share);

  	mnt->mnt_group_id = 0;

  
  	if (peer_mnt)
  		master = peer_mnt;
  
  	if (master) {

  		list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)

  			slave_mnt->mnt_master = master;

  		list_move(&mnt->mnt_slave, &master->mnt_slave_list);
  		list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
  		INIT_LIST_HEAD(&mnt->mnt_slave_list);

  	} else {

  		struct list_head *p = &mnt->mnt_slave_list;

  		while (!list_empty(p)) {

                          slave_mnt = list_first_entry(p,

  					struct mount, mnt_slave);
  			list_del_init(&slave_mnt->mnt_slave);

  			slave_mnt->mnt_master = NULL;
  		}
  	}

  	mnt->mnt_master = master;

  	CLEAR_MNT_SHARED(mnt);

  	return 0;
  }

  /*
   * vfsmount lock must be held for write
   */

  void change_mnt_propagation(struct mount *mnt, int type)

  {

  	if (type == MS_SHARED) {

  		set_mnt_shared(mnt);

  		return;
  	}

  	do_make_slave(mnt);

  	if (type != MS_SLAVE) {

  		list_del_init(&mnt->mnt_slave);

  		mnt->mnt_master = NULL;

  		if (type == MS_UNBINDABLE)

  			mnt->mnt.mnt_flags |= MNT_UNBINDABLE;

  		else

  			mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;

  	}

  }

  
  /*
   * get the next mount in the propagation tree.
   * @m: the mount seen last
   * @origin: the original mount from where the tree walk initiated

   *
   * Note that peer groups form contiguous segments of slave lists.
   * We rely on that in get_source() to be able to find out if
   * vfsmount found while iterating with propagation_next() is
   * a peer of one we'd found earlier.

   */

  static struct mount *propagation_next(struct mount *m,
  					 struct mount *origin)

  {

  	/* are there any slaves of this mount? */

  	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))

  		return first_slave(m);
  
  	while (1) {

  		struct mount *master = m->mnt_master;

  		if (master == origin->mnt_master) {

  			struct mount *next = next_peer(m);
  			return (next == origin) ? NULL : next;

  		} else if (m->mnt_slave.next != &master->mnt_slave_list)

  			return next_slave(m);
  
  		/* back at master */
  		m = master;
  	}
  }
  
  /*
   * return the source mount to be used for cloning
   *
   * @dest 	the current destination mount
   * @last_dest  	the last seen destination mount
   * @last_src  	the last seen source mount
   * @type	return CL_SLAVE if the new mount has to be
   * 		cloned as a slave.
   */

  static struct mount *get_source(struct mount *dest,
  				struct mount *last_dest,
  				struct mount *last_src,
  				int *type)

  {

  	struct mount *p_last_src = NULL;
  	struct mount *p_last_dest = NULL;

  	while (last_dest != dest->mnt_master) {

  		p_last_dest = last_dest;
  		p_last_src = last_src;

  		last_dest = last_dest->mnt_master;
  		last_src = last_src->mnt_master;

  	}
  
  	if (p_last_dest) {
  		do {
  			p_last_dest = next_peer(p_last_dest);

  		} while (IS_MNT_NEW(p_last_dest));

  		/* is that a peer of the earlier? */
  		if (dest == p_last_dest) {
  			*type = CL_MAKE_SHARED;
  			return p_last_src;
  		}

  	}

  	/* slave of the earlier, then */
  	*type = CL_SLAVE;
  	/* beginning of peer group among the slaves? */

  	if (IS_MNT_SHARED(dest))

  		*type |= CL_MAKE_SHARED;
  	return last_src;

  }
  
  /*
   * mount 'source_mnt' under the destination 'dest_mnt' at
   * dentry 'dest_dentry'. And propagate that mount to
   * all the peer and slave mounts of 'dest_mnt'.
   * Link all the new mounts into a propagation tree headed at
   * source_mnt. Also link all the new mounts using ->mnt_list
   * headed at source_mnt's ->mnt_list
   *
   * @dest_mnt: destination mount.
   * @dest_dentry: destination dentry.
   * @source_mnt: source mount.
   * @tree_list : list of heads of trees to be attached.
   */

  int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,

  		    struct mount *source_mnt, struct list_head *tree_list)

  {

  	struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;

  	struct mount *m, *child;

  	int ret = 0;

  	struct mount *prev_dest_mnt = dest_mnt;
  	struct mount *prev_src_mnt  = source_mnt;

  	LIST_HEAD(tmp_list);

  	for (m = propagation_next(dest_mnt, dest_mnt); m;
  			m = propagation_next(m, dest_mnt)) {

  		int type;

  		struct mount *source;

  		if (IS_MNT_NEW(m))

  			continue;

  		source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);

  		/* Notice when we are propagating across user namespaces */
  		if (m->mnt_ns->user_ns != user_ns)
  			type |= CL_UNPRIVILEGED;

  		child = copy_tree(source, source->mnt.mnt_root, type);
  		if (IS_ERR(child)) {
  			ret = PTR_ERR(child);

  			list_splice(tree_list, tmp_list.prev);
  			goto out;
  		}

  		if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) {
  			mnt_set_mountpoint(m, dest_mp, child);

  			list_add_tail(&child->mnt_hash, tree_list);

  		} else {
  			/*
  			 * This can happen if the parent mount was bind mounted
  			 * on some subdirectory of a shared/slave mount.
  			 */

  			list_add_tail(&child->mnt_hash, &tmp_list);

  		}
  		prev_dest_mnt = m;

  		prev_src_mnt  = child;

  	}
  out:

  	lock_mount_hash();

  	while (!list_empty(&tmp_list)) {

  		child = list_first_entry(&tmp_list, struct mount, mnt_hash);

  		umount_tree(child, 0);

  	}

  	unlock_mount_hash();

  	return ret;
  }

  
  /*
   * return true if the refcount is greater than count
   */

  static inline int do_refcount_check(struct mount *mnt, int count)

  {

  	return mnt_get_count(mnt) > count;

  }
  
  /*
   * check if the mount 'mnt' can be unmounted successfully.
   * @mnt: the mount to be checked for unmount
   * NOTE: unmounting 'mnt' would naturally propagate to all
   * other mounts its parent propagates to.
   * Check if any of these mounts that **do not have submounts**
   * have more references than 'refcnt'. If so return busy.

   *

   * vfsmount lock must be held for write

   */

  int propagate_mount_busy(struct mount *mnt, int refcnt)

  {

  	struct mount *m, *child;

  	struct mount *parent = mnt->mnt_parent;

  	int ret = 0;

  	if (mnt == parent)

  		return do_refcount_check(mnt, refcnt);
  
  	/*
  	 * quickly check if the current mount can be unmounted.
  	 * If not, we don't have to go checking for all other
  	 * mounts
  	 */

  	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))

  		return 1;

  	for (m = propagation_next(parent, parent); m;
  	     		m = propagation_next(m, parent)) {

  		child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);

  		if (child && list_empty(&child->mnt_mounts) &&

  		    (ret = do_refcount_check(child, 1)))

  			break;
  	}
  	return ret;
  }
  
  /*
   * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
   * parent propagates to.
   */

  static void __propagate_umount(struct mount *mnt)

  {

  	struct mount *parent = mnt->mnt_parent;

  	struct mount *m;

  	BUG_ON(parent == mnt);

  	for (m = propagation_next(parent, parent); m;
  			m = propagation_next(m, parent)) {

  		struct mount *child = __lookup_mnt_last(&m->mnt,
  						mnt->mnt_mountpoint);

  		/*
  		 * umount the child only if the child has no
  		 * other children
  		 */

  		if (child && list_empty(&child->mnt_mounts))

  			list_move_tail(&child->mnt_hash, &mnt->mnt_hash);

  	}
  }
  
  /*
   * collect all mounts that receive propagation from the mount in @list,
   * and return these additional mounts in the same list.
   * @list: the list of mounts to be unmounted.

   *
   * vfsmount lock must be held for write

   */
  int propagate_umount(struct list_head *list)
  {

  	struct mount *mnt;

  	list_for_each_entry(mnt, list, mnt_hash)

  		__propagate_umount(mnt);
  	return 0;
  }