/*
   *  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 "internal.h"

  #include "pnode.h"

  /* return the next shared peer mount of @p */
  static inline struct vfsmount *next_peer(struct vfsmount *p)
  {
  	return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
  }

  static inline struct vfsmount *first_slave(struct vfsmount *p)
  {
  	return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
  }
  
  static inline struct vfsmount *next_slave(struct vfsmount *p)
  {
  	return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
  }

  /*
   * Return true if path is reachable from root
   *
   * namespace_sem is held, and mnt is attached
   */
  static bool is_path_reachable(struct vfsmount *mnt, struct dentry *dentry,
  			 const struct path *root)
  {
  	while (mnt != root->mnt && mnt->mnt_parent != mnt) {
  		dentry = mnt->mnt_mountpoint;
  		mnt = mnt->mnt_parent;
  	}
  	return mnt == root->mnt && is_subdir(dentry, root->dentry);
  }
  
  static struct vfsmount *get_peer_under_root(struct vfsmount *mnt,
  					    struct mnt_namespace *ns,
  					    const struct path *root)
  {
  	struct vfsmount *m = mnt;
  
  	do {
  		/* Check the namespace first for optimization */
  		if (m->mnt_ns == ns && is_path_reachable(m, m->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 vfsmount *mnt, const struct path *root)
  {
  	struct vfsmount *m;
  
  	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
  		struct vfsmount *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 vfsmount *mnt)
  {
  	struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
  	struct vfsmount *slave_mnt;
  
  	/*
  	 * slave 'mnt' to a peer mount that has the
  	 * same root dentry. If none is available than
  	 * slave it to anything that is available.
  	 */
  	while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
  	       peer_mnt->mnt_root != mnt->mnt_root) ;
  
  	if (peer_mnt == mnt) {
  		peer_mnt = next_peer(mnt);
  		if (peer_mnt == mnt)
  			peer_mnt = NULL;
  	}

  	if (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 vfsmount, mnt_slave);
  			list_del_init(&slave_mnt->mnt_slave);
  			slave_mnt->mnt_master = NULL;
  		}
  	}
  	mnt->mnt_master = master;
  	CLEAR_MNT_SHARED(mnt);

  	return 0;
  }

  void change_mnt_propagation(struct vfsmount *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_flags |= MNT_UNBINDABLE;

  		else
  			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
   */
  static struct vfsmount *propagation_next(struct vfsmount *m,
  					 struct vfsmount *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 vfsmount *next;
  		struct vfsmount *master = m->mnt_master;

  		if (master == origin->mnt_master) {

  			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 vfsmount *get_source(struct vfsmount *dest,
  					struct vfsmount *last_dest,
  					struct vfsmount *last_src,
  					int *type)
  {
  	struct vfsmount *p_last_src = NULL;
  	struct vfsmount *p_last_dest = NULL;

  	*type = CL_PROPAGATION;

  
  	if (IS_MNT_SHARED(dest))
  		*type |= CL_MAKE_SHARED;
  
  	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));
  	}
  
  	if (dest != p_last_dest) {
  		*type |= CL_SLAVE;
  		return last_src;
  	} else
  		return p_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 vfsmount *dest_mnt, struct dentry *dest_dentry,
  		    struct vfsmount *source_mnt, struct list_head *tree_list)
  {
  	struct vfsmount *m, *child;
  	int ret = 0;
  	struct vfsmount *prev_dest_mnt = dest_mnt;
  	struct vfsmount *prev_src_mnt  = source_mnt;
  	LIST_HEAD(tmp_list);
  	LIST_HEAD(umount_list);
  
  	for (m = propagation_next(dest_mnt, dest_mnt); m;
  			m = propagation_next(m, dest_mnt)) {

  		int type;
  		struct vfsmount *source;

  
  		if (IS_MNT_NEW(m))
  			continue;

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

  		if (!(child = copy_tree(source, source->mnt_root, type))) {

  			ret = -ENOMEM;
  			list_splice(tree_list, tmp_list.prev);
  			goto out;
  		}
  
  		if (is_subdir(dest_dentry, m->mnt_root)) {
  			mnt_set_mountpoint(m, dest_dentry, 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:
  	spin_lock(&vfsmount_lock);
  	while (!list_empty(&tmp_list)) {

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

  		umount_tree(child, 0, &umount_list);

  	}
  	spin_unlock(&vfsmount_lock);
  	release_mounts(&umount_list);
  	return ret;
  }

  
  /*
   * return true if the refcount is greater than count
   */
  static inline int do_refcount_check(struct vfsmount *mnt, int count)
  {

  	int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;

  	return (mycount > 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.
   */
  int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
  {
  	struct vfsmount *m, *child;
  	struct vfsmount *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(m, mnt->mnt_mountpoint, 0);
  		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 vfsmount *mnt)
  {
  	struct vfsmount *parent = mnt->mnt_parent;
  	struct vfsmount *m;
  
  	BUG_ON(parent == mnt);
  
  	for (m = propagation_next(parent, parent); m;
  			m = propagation_next(m, parent)) {
  
  		struct vfsmount *child = __lookup_mnt(m,
  					mnt->mnt_mountpoint, 0);
  		/*
  		 * 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.
   */
  int propagate_umount(struct list_head *list)
  {
  	struct vfsmount *mnt;
  
  	list_for_each_entry(mnt, list, mnt_hash)
  		__propagate_umount(mnt);
  	return 0;
  }