/*
   * This file is part of UBIFS.
   *
   * Copyright (C) 2006-2008 Nokia Corporation.
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 as published by
   * the Free Software Foundation.
   *
   * This program is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
   * more details.
   *
   * You should have received a copy of the GNU General Public License along with
   * this program; if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
   *
   * Authors: Artem Bityutskiy (Битюцкий Артём)
   *          Adrian Hunter
   */
  
  /*
   * This file contains functions for finding LEBs for various purposes e.g.
   * garbage collection. In general, lprops category heaps and lists are used
   * for fast access, falling back on scanning the LPT as a last resort.
   */
  
  #include <linux/sort.h>
  #include "ubifs.h"
  
  /**
   * struct scan_data - data provided to scan callback functions
   * @min_space: minimum number of bytes for which to scan
   * @pick_free: whether it is OK to scan for empty LEBs
   * @lnum: LEB number found is returned here
   * @exclude_index: whether to exclude index LEBs
   */
  struct scan_data {
  	int min_space;
  	int pick_free;
  	int lnum;
  	int exclude_index;
  };
  
  /**
   * valuable - determine whether LEB properties are valuable.
   * @c: the UBIFS file-system description object
   * @lprops: LEB properties
   *
   * This function return %1 if the LEB properties should be added to the LEB
   * properties tree in memory. Otherwise %0 is returned.
   */
  static int valuable(struct ubifs_info *c, const struct ubifs_lprops *lprops)
  {
  	int n, cat = lprops->flags & LPROPS_CAT_MASK;
  	struct ubifs_lpt_heap *heap;
  
  	switch (cat) {
  	case LPROPS_DIRTY:
  	case LPROPS_DIRTY_IDX:
  	case LPROPS_FREE:
  		heap = &c->lpt_heap[cat - 1];
  		if (heap->cnt < heap->max_cnt)
  			return 1;
  		if (lprops->free + lprops->dirty >= c->dark_wm)
  			return 1;
  		return 0;
  	case LPROPS_EMPTY:
  		n = c->lst.empty_lebs + c->freeable_cnt -
  		    c->lst.taken_empty_lebs;
  		if (n < c->lsave_cnt)
  			return 1;
  		return 0;
  	case LPROPS_FREEABLE:
  		return 1;
  	case LPROPS_FRDI_IDX:
  		return 1;
  	}
  	return 0;
  }
  
  /**
   * scan_for_dirty_cb - dirty space scan callback.
   * @c: the UBIFS file-system description object
   * @lprops: LEB properties to scan
   * @in_tree: whether the LEB properties are in main memory
   * @data: information passed to and from the caller of the scan
   *
   * This function returns a code that indicates whether the scan should continue
   * (%LPT_SCAN_CONTINUE), whether the LEB properties should be added to the tree
   * in main memory (%LPT_SCAN_ADD), or whether the scan should stop
   * (%LPT_SCAN_STOP).
   */
  static int scan_for_dirty_cb(struct ubifs_info *c,
  			     const struct ubifs_lprops *lprops, int in_tree,
  			     struct scan_data *data)
  {
  	int ret = LPT_SCAN_CONTINUE;
  
  	/* Exclude LEBs that are currently in use */
  	if (lprops->flags & LPROPS_TAKEN)
  		return LPT_SCAN_CONTINUE;
  	/* Determine whether to add these LEB properties to the tree */
  	if (!in_tree && valuable(c, lprops))
  		ret |= LPT_SCAN_ADD;
  	/* Exclude LEBs with too little space */
  	if (lprops->free + lprops->dirty < data->min_space)
  		return ret;
  	/* If specified, exclude index LEBs */
  	if (data->exclude_index && lprops->flags & LPROPS_INDEX)
  		return ret;
  	/* If specified, exclude empty or freeable LEBs */
  	if (lprops->free + lprops->dirty == c->leb_size) {
  		if (!data->pick_free)
  			return ret;
  	/* Exclude LEBs with too little dirty space (unless it is empty) */
  	} else if (lprops->dirty < c->dead_wm)
  		return ret;
  	/* Finally we found space */
  	data->lnum = lprops->lnum;
  	return LPT_SCAN_ADD | LPT_SCAN_STOP;
  }
  
  /**
   * scan_for_dirty - find a data LEB with free space.
   * @c: the UBIFS file-system description object
   * @min_space: minimum amount free plus dirty space the returned LEB has to
   *             have
   * @pick_free: if it is OK to return a free or freeable LEB
   * @exclude_index: whether to exclude index LEBs
   *
   * This function returns a pointer to the LEB properties found or a negative
   * error code.
   */
  static const struct ubifs_lprops *scan_for_dirty(struct ubifs_info *c,
  						 int min_space, int pick_free,
  						 int exclude_index)
  {
  	const struct ubifs_lprops *lprops;
  	struct ubifs_lpt_heap *heap;
  	struct scan_data data;
  	int err, i;
  
  	/* There may be an LEB with enough dirty space on the free heap */
  	heap = &c->lpt_heap[LPROPS_FREE - 1];
  	for (i = 0; i < heap->cnt; i++) {
  		lprops = heap->arr[i];
  		if (lprops->free + lprops->dirty < min_space)
  			continue;
  		if (lprops->dirty < c->dead_wm)
  			continue;
  		return lprops;
  	}
  	/*
  	 * A LEB may have fallen off of the bottom of the dirty heap, and ended
  	 * up as uncategorized even though it has enough dirty space for us now,
  	 * so check the uncategorized list. N.B. neither empty nor freeable LEBs
  	 * can end up as uncategorized because they are kept on lists not
  	 * finite-sized heaps.
  	 */
  	list_for_each_entry(lprops, &c->uncat_list, list) {
  		if (lprops->flags & LPROPS_TAKEN)
  			continue;
  		if (lprops->free + lprops->dirty < min_space)
  			continue;
  		if (exclude_index && (lprops->flags & LPROPS_INDEX))
  			continue;
  		if (lprops->dirty < c->dead_wm)
  			continue;
  		return lprops;
  	}
  	/* We have looked everywhere in main memory, now scan the flash */
  	if (c->pnodes_have >= c->pnode_cnt)
  		/* All pnodes are in memory, so skip scan */
  		return ERR_PTR(-ENOSPC);
  	data.min_space = min_space;
  	data.pick_free = pick_free;
  	data.lnum = -1;
  	data.exclude_index = exclude_index;
  	err = ubifs_lpt_scan_nolock(c, -1, c->lscan_lnum,
  				    (ubifs_lpt_scan_callback)scan_for_dirty_cb,
  				    &data);
  	if (err)
  		return ERR_PTR(err);
  	ubifs_assert(data.lnum >= c->main_first && data.lnum < c->leb_cnt);
  	c->lscan_lnum = data.lnum;
  	lprops = ubifs_lpt_lookup_dirty(c, data.lnum);
  	if (IS_ERR(lprops))
  		return lprops;
  	ubifs_assert(lprops->lnum == data.lnum);
  	ubifs_assert(lprops->free + lprops->dirty >= min_space);
  	ubifs_assert(lprops->dirty >= c->dead_wm ||
  		     (pick_free &&
  		      lprops->free + lprops->dirty == c->leb_size));
  	ubifs_assert(!(lprops->flags & LPROPS_TAKEN));
  	ubifs_assert(!exclude_index || !(lprops->flags & LPROPS_INDEX));
  	return lprops;
  }
  
  /**
   * ubifs_find_dirty_leb - find a dirty LEB for the Garbage Collector.
   * @c: the UBIFS file-system description object
   * @ret_lp: LEB properties are returned here on exit
   * @min_space: minimum amount free plus dirty space the returned LEB has to
   *             have
   * @pick_free: controls whether it is OK to pick empty or index LEBs
   *
   * This function tries to find a dirty logical eraseblock which has at least
   * @min_space free and dirty space. It prefers to take an LEB from the dirty or
   * dirty index heap, and it falls-back to LPT scanning if the heaps are empty
   * or do not have an LEB which satisfies the @min_space criteria.
   *
   * Note, LEBs which have less than dead watermark of free + dirty space are
   * never picked by this function.
   *
   * The additional @pick_free argument controls if this function has to return a
   * free or freeable LEB if one is present. For example, GC must to set it to %1,
   * when called from the journal space reservation function, because the
   * appearance of free space may coincide with the loss of enough dirty space
   * for GC to succeed anyway.
   *
   * In contrast, if the Garbage Collector is called from budgeting, it should
   * just make free space, not return LEBs which are already free or freeable.
   *
   * In addition @pick_free is set to %2 by the recovery process in order to
   * recover gc_lnum in which case an index LEB must not be returned.
   *
   * This function returns zero and the LEB properties of found dirty LEB in case
   * of success, %-ENOSPC if no dirty LEB was found and a negative error code in
   * case of other failures. The returned LEB is marked as "taken".
   */
  int ubifs_find_dirty_leb(struct ubifs_info *c, struct ubifs_lprops *ret_lp,
  			 int min_space, int pick_free)
  {
  	int err = 0, sum, exclude_index = pick_free == 2 ? 1 : 0;
  	const struct ubifs_lprops *lp = NULL, *idx_lp = NULL;
  	struct ubifs_lpt_heap *heap, *idx_heap;
  
  	ubifs_get_lprops(c);
  
  	if (pick_free) {
  		int lebs, rsvd_idx_lebs = 0;
  
  		spin_lock(&c->space_lock);
  		lebs = c->lst.empty_lebs + c->idx_gc_cnt;
  		lebs += c->freeable_cnt - c->lst.taken_empty_lebs;
  
  		/*
  		 * Note, the index may consume more LEBs than have been reserved
  		 * for it. It is OK because it might be consolidated by GC.
  		 * But if the index takes fewer LEBs than it is reserved for it,
  		 * this function must avoid picking those reserved LEBs.
  		 */
  		if (c->bi.min_idx_lebs >= c->lst.idx_lebs) {
  			rsvd_idx_lebs = c->bi.min_idx_lebs -  c->lst.idx_lebs;
  			exclude_index = 1;
  		}
  		spin_unlock(&c->space_lock);
  
  		/* Check if there are enough free LEBs for the index */
  		if (rsvd_idx_lebs < lebs) {
  			/* OK, try to find an empty LEB */
  			lp = ubifs_fast_find_empty(c);
  			if (lp)
  				goto found;
  
  			/* Or a freeable LEB */
  			lp = ubifs_fast_find_freeable(c);
  			if (lp)
  				goto found;
  		} else
  			/*
  			 * We cannot pick free/freeable LEBs in the below code.
  			 */
  			pick_free = 0;
  	} else {
  		spin_lock(&c->space_lock);
  		exclude_index = (c->bi.min_idx_lebs >= c->lst.idx_lebs);
  		spin_unlock(&c->space_lock);
  	}
  
  	/* Look on the dirty and dirty index heaps */
  	heap = &c->lpt_heap[LPROPS_DIRTY - 1];
  	idx_heap = &c->lpt_heap[LPROPS_DIRTY_IDX - 1];
  
  	if (idx_heap->cnt && !exclude_index) {
  		idx_lp = idx_heap->arr[0];
  		sum = idx_lp->free + idx_lp->dirty;
  		/*
  		 * Since we reserve thrice as much space for the index than it
  		 * actually takes, it does not make sense to pick indexing LEBs
  		 * with less than, say, half LEB of dirty space. May be half is
  		 * not the optimal boundary - this should be tested and
  		 * checked. This boundary should determine how much we use
  		 * in-the-gaps to consolidate the index comparing to how much
  		 * we use garbage collector to consolidate it. The "half"
  		 * criteria just feels to be fine.
  		 */
  		if (sum < min_space || sum < c->half_leb_size)
  			idx_lp = NULL;
  	}
  
  	if (heap->cnt) {
  		lp = heap->arr[0];
  		if (lp->dirty + lp->free < min_space)
  			lp = NULL;
  	}
  
  	/* Pick the LEB with most space */
  	if (idx_lp && lp) {
  		if (idx_lp->free + idx_lp->dirty >= lp->free + lp->dirty)
  			lp = idx_lp;
  	} else if (idx_lp && !lp)
  		lp = idx_lp;
  
  	if (lp) {
  		ubifs_assert(lp->free + lp->dirty >= c->dead_wm);
  		goto found;
  	}
  
  	/* Did not find a dirty LEB on the dirty heaps, have to scan */
  	dbg_find("scanning LPT for a dirty LEB");
  	lp = scan_for_dirty(c, min_space, pick_free, exclude_index);
  	if (IS_ERR(lp)) {
  		err = PTR_ERR(lp);
  		goto out;
  	}
  	ubifs_assert(lp->dirty >= c->dead_wm ||
  		     (pick_free && lp->free + lp->dirty == c->leb_size));
  
  found:
  	dbg_find("found LEB %d, free %d, dirty %d, flags %#x",
  		 lp->lnum, lp->free, lp->dirty, lp->flags);
  
  	lp = ubifs_change_lp(c, lp, LPROPS_NC, LPROPS_NC,
  			     lp->flags | LPROPS_TAKEN, 0);
  	if (IS_ERR(lp)) {
  		err = PTR_ERR(lp);
  		goto out;
  	}
  
  	memcpy(ret_lp, lp, sizeof(struct ubifs_lprops));
  
  out:
  	ubifs_release_lprops(c);
  	return err;
  }
  
  /**
   * scan_for_free_cb - free space scan callback.
   * @c: the UBIFS file-system description object
   * @lprops: LEB properties to scan
   * @in_tree: whether the LEB properties are in main memory
   * @data: information passed to and from the caller of the scan
   *
   * This function returns a code that indicates whether the scan should continue
   * (%LPT_SCAN_CONTINUE), whether the LEB properties should be added to the tree
   * in main memory (%LPT_SCAN_ADD), or whether the scan should stop
   * (%LPT_SCAN_STOP).
   */
  static int scan_for_free_cb(struct ubifs_info *c,
  			    const struct ubifs_lprops *lprops, int in_tree,
  			    struct scan_data *data)
  {
  	int ret = LPT_SCAN_CONTINUE;
  
  	/* Exclude LEBs that are currently in use */
  	if (lprops->flags & LPROPS_TAKEN)
  		return LPT_SCAN_CONTINUE;
  	/* Determine whether to add these LEB properties to the tree */
  	if (!in_tree && valuable(c, lprops))
  		ret |= LPT_SCAN_ADD;
  	/* Exclude index LEBs */
  	if (lprops->flags & LPROPS_INDEX)
  		return ret;
  	/* Exclude LEBs with too little space */
  	if (lprops->free < data->min_space)
  		return ret;
  	/* If specified, exclude empty LEBs */
  	if (!data->pick_free && lprops->free == c->leb_size)
  		return ret;
  	/*
  	 * LEBs that have only free and dirty space must not be allocated
  	 * because they may have been unmapped already or they may have data
  	 * that is obsolete only because of nodes that are still sitting in a
  	 * wbuf.
  	 */
  	if (lprops->free + lprops->dirty == c->leb_size && lprops->dirty > 0)
  		return ret;
  	/* Finally we found space */
  	data->lnum = lprops->lnum;
  	return LPT_SCAN_ADD | LPT_SCAN_STOP;
  }
  
  /**
   * do_find_free_space - find a data LEB with free space.
   * @c: the UBIFS file-system description object
   * @min_space: minimum amount of free space required
   * @pick_free: whether it is OK to scan for empty LEBs
   * @squeeze: whether to try to find space in a non-empty LEB first
   *
   * This function returns a pointer to the LEB properties found or a negative
   * error code.
   */
  static
  const struct ubifs_lprops *do_find_free_space(struct ubifs_info *c,
  					      int min_space, int pick_free,
  					      int squeeze)
  {
  	const struct ubifs_lprops *lprops;
  	struct ubifs_lpt_heap *heap;
  	struct scan_data data;
  	int err, i;
  
  	if (squeeze) {
  		lprops = ubifs_fast_find_free(c);
  		if (lprops && lprops->free >= min_space)
  			return lprops;
  	}
  	if (pick_free) {
  		lprops = ubifs_fast_find_empty(c);
  		if (lprops)
  			return lprops;
  	}
  	if (!squeeze) {
  		lprops = ubifs_fast_find_free(c);
  		if (lprops && lprops->free >= min_space)
  			return lprops;
  	}
  	/* There may be an LEB with enough free space on the dirty heap */
  	heap = &c->lpt_heap[LPROPS_DIRTY - 1];
  	for (i = 0; i < heap->cnt; i++) {
  		lprops = heap->arr[i];
  		if (lprops->free >= min_space)
  			return lprops;
  	}
  	/*
  	 * A LEB may have fallen off of the bottom of the free heap, and ended
  	 * up as uncategorized even though it has enough free space for us now,
  	 * so check the uncategorized list. N.B. neither empty nor freeable LEBs
  	 * can end up as uncategorized because they are kept on lists not
  	 * finite-sized heaps.
  	 */
  	list_for_each_entry(lprops, &c->uncat_list, list) {
  		if (lprops->flags & LPROPS_TAKEN)
  			continue;
  		if (lprops->flags & LPROPS_INDEX)
  			continue;
  		if (lprops->free >= min_space)
  			return lprops;
  	}
  	/* We have looked everywhere in main memory, now scan the flash */
  	if (c->pnodes_have >= c->pnode_cnt)
  		/* All pnodes are in memory, so skip scan */
  		return ERR_PTR(-ENOSPC);
  	data.min_space = min_space;
  	data.pick_free = pick_free;
  	data.lnum = -1;
  	err = ubifs_lpt_scan_nolock(c, -1, c->lscan_lnum,
  				    (ubifs_lpt_scan_callback)scan_for_free_cb,
  				    &data);
  	if (err)
  		return ERR_PTR(err);
  	ubifs_assert(data.lnum >= c->main_first && data.lnum < c->leb_cnt);
  	c->lscan_lnum = data.lnum;
  	lprops = ubifs_lpt_lookup_dirty(c, data.lnum);
  	if (IS_ERR(lprops))
  		return lprops;
  	ubifs_assert(lprops->lnum == data.lnum);
  	ubifs_assert(lprops->free >= min_space);
  	ubifs_assert(!(lprops->flags & LPROPS_TAKEN));
  	ubifs_assert(!(lprops->flags & LPROPS_INDEX));
  	return lprops;
  }
  
  /**
   * ubifs_find_free_space - find a data LEB with free space.
   * @c: the UBIFS file-system description object
   * @min_space: minimum amount of required free space
   * @offs: contains offset of where free space starts on exit
   * @squeeze: whether to try to find space in a non-empty LEB first
   *
   * This function looks for an LEB with at least @min_space bytes of free space.
   * It tries to find an empty LEB if possible. If no empty LEBs are available,
   * this function searches for a non-empty data LEB. The returned LEB is marked
   * as "taken".
   *
   * This function returns found LEB number in case of success, %-ENOSPC if it
   * failed to find a LEB with @min_space bytes of free space and other a negative
   * error codes in case of failure.
   */
  int ubifs_find_free_space(struct ubifs_info *c, int min_space, int *offs,
  			  int squeeze)
  {
  	const struct ubifs_lprops *lprops;
  	int lebs, rsvd_idx_lebs, pick_free = 0, err, lnum, flags;
  
  	dbg_find("min_space %d", min_space);
  	ubifs_get_lprops(c);
  
  	/* Check if there are enough empty LEBs for commit */
  	spin_lock(&c->space_lock);
  	if (c->bi.min_idx_lebs > c->lst.idx_lebs)
  		rsvd_idx_lebs = c->bi.min_idx_lebs -  c->lst.idx_lebs;
  	else
  		rsvd_idx_lebs = 0;
  	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
  	       c->lst.taken_empty_lebs;
  	if (rsvd_idx_lebs < lebs)
  		/*
  		 * OK to allocate an empty LEB, but we still don't want to go
  		 * looking for one if there aren't any.
  		 */
  		if (c->lst.empty_lebs - c->lst.taken_empty_lebs > 0) {
  			pick_free = 1;
  			/*
  			 * Because we release the space lock, we must account
  			 * for this allocation here. After the LEB properties
  			 * flags have been updated, we subtract one. Note, the
  			 * result of this is that lprops also decreases
  			 * @taken_empty_lebs in 'ubifs_change_lp()', so it is
  			 * off by one for a short period of time which may
  			 * introduce a small disturbance to budgeting
  			 * calculations, but this is harmless because at the
  			 * worst case this would make the budgeting subsystem
  			 * be more pessimistic than needed.
  			 *
  			 * Fundamentally, this is about serialization of the
  			 * budgeting and lprops subsystems. We could make the
  			 * @space_lock a mutex and avoid dropping it before
  			 * calling 'ubifs_change_lp()', but mutex is more
  			 * heavy-weight, and we want budgeting to be as fast as
  			 * possible.
  			 */
  			c->lst.taken_empty_lebs += 1;
  		}
  	spin_unlock(&c->space_lock);
  
  	lprops = do_find_free_space(c, min_space, pick_free, squeeze);
  	if (IS_ERR(lprops)) {
  		err = PTR_ERR(lprops);
  		goto out;
  	}
  
  	lnum = lprops->lnum;
  	flags = lprops->flags | LPROPS_TAKEN;
  
  	lprops = ubifs_change_lp(c, lprops, LPROPS_NC, LPROPS_NC, flags, 0);
  	if (IS_ERR(lprops)) {
  		err = PTR_ERR(lprops);
  		goto out;
  	}
  
  	if (pick_free) {
  		spin_lock(&c->space_lock);
  		c->lst.taken_empty_lebs -= 1;
  		spin_unlock(&c->space_lock);
  	}
  
  	*offs = c->leb_size - lprops->free;
  	ubifs_release_lprops(c);
  
  	if (*offs == 0) {
  		/*
  		 * Ensure that empty LEBs have been unmapped. They may not have
  		 * been, for example, because of an unclean unmount.  Also
  		 * LEBs that were freeable LEBs (free + dirty == leb_size) will
  		 * not have been unmapped.
  		 */
  		err = ubifs_leb_unmap(c, lnum);
  		if (err)
  			return err;
  	}
  
  	dbg_find("found LEB %d, free %d", lnum, c->leb_size - *offs);
  	ubifs_assert(*offs <= c->leb_size - min_space);
  	return lnum;
  
  out:
  	if (pick_free) {
  		spin_lock(&c->space_lock);
  		c->lst.taken_empty_lebs -= 1;
  		spin_unlock(&c->space_lock);
  	}
  	ubifs_release_lprops(c);
  	return err;
  }
  
  /**
   * scan_for_idx_cb - callback used by the scan for a free LEB for the index.
   * @c: the UBIFS file-system description object
   * @lprops: LEB properties to scan
   * @in_tree: whether the LEB properties are in main memory
   * @data: information passed to and from the caller of the scan
   *
   * This function returns a code that indicates whether the scan should continue
   * (%LPT_SCAN_CONTINUE), whether the LEB properties should be added to the tree
   * in main memory (%LPT_SCAN_ADD), or whether the scan should stop
   * (%LPT_SCAN_STOP).
   */
  static int scan_for_idx_cb(struct ubifs_info *c,
  			   const struct ubifs_lprops *lprops, int in_tree,
  			   struct scan_data *data)
  {
  	int ret = LPT_SCAN_CONTINUE;
  
  	/* Exclude LEBs that are currently in use */
  	if (lprops->flags & LPROPS_TAKEN)
  		return LPT_SCAN_CONTINUE;
  	/* Determine whether to add these LEB properties to the tree */
  	if (!in_tree && valuable(c, lprops))
  		ret |= LPT_SCAN_ADD;
  	/* Exclude index LEBS */
  	if (lprops->flags & LPROPS_INDEX)
  		return ret;
  	/* Exclude LEBs that cannot be made empty */
  	if (lprops->free + lprops->dirty != c->leb_size)
  		return ret;
  	/*
  	 * We are allocating for the index so it is safe to allocate LEBs with
  	 * only free and dirty space, because write buffers are sync'd at commit
  	 * start.
  	 */
  	data->lnum = lprops->lnum;
  	return LPT_SCAN_ADD | LPT_SCAN_STOP;
  }
  
  /**
   * scan_for_leb_for_idx - scan for a free LEB for the index.
   * @c: the UBIFS file-system description object
   */
  static const struct ubifs_lprops *scan_for_leb_for_idx(struct ubifs_info *c)
  {
  	struct ubifs_lprops *lprops;
  	struct scan_data data;
  	int err;
  
  	data.lnum = -1;
  	err = ubifs_lpt_scan_nolock(c, -1, c->lscan_lnum,
  				    (ubifs_lpt_scan_callback)scan_for_idx_cb,
  				    &data);
  	if (err)
  		return ERR_PTR(err);
  	ubifs_assert(data.lnum >= c->main_first && data.lnum < c->leb_cnt);
  	c->lscan_lnum = data.lnum;
  	lprops = ubifs_lpt_lookup_dirty(c, data.lnum);
  	if (IS_ERR(lprops))
  		return lprops;
  	ubifs_assert(lprops->lnum == data.lnum);
  	ubifs_assert(lprops->free + lprops->dirty == c->leb_size);
  	ubifs_assert(!(lprops->flags & LPROPS_TAKEN));
  	ubifs_assert(!(lprops->flags & LPROPS_INDEX));
  	return lprops;
  }
  
  /**
   * ubifs_find_free_leb_for_idx - find a free LEB for the index.
   * @c: the UBIFS file-system description object
   *
   * This function looks for a free LEB and returns that LEB number. The returned
   * LEB is marked as "taken", "index".
   *
   * Only empty LEBs are allocated. This is for two reasons. First, the commit
   * calculates the number of LEBs to allocate based on the assumption that they
   * will be empty. Secondly, free space at the end of an index LEB is not
   * guaranteed to be empty because it may have been used by the in-the-gaps
   * method prior to an unclean unmount.
   *
   * If no LEB is found %-ENOSPC is returned. For other failures another negative
   * error code is returned.
   */
  int ubifs_find_free_leb_for_idx(struct ubifs_info *c)
  {
  	const struct ubifs_lprops *lprops;
  	int lnum = -1, err, flags;
  
  	ubifs_get_lprops(c);
  
  	lprops = ubifs_fast_find_empty(c);
  	if (!lprops) {
  		lprops = ubifs_fast_find_freeable(c);
  		if (!lprops) {
  			/*
  			 * The first condition means the following: go scan the
  			 * LPT if there are uncategorized lprops, which means
  			 * there may be freeable LEBs there (UBIFS does not
  			 * store the information about freeable LEBs in the
  			 * master node).
  			 */
  			if (c->in_a_category_cnt != c->main_lebs ||
  			    c->lst.empty_lebs - c->lst.taken_empty_lebs > 0) {
  				ubifs_assert(c->freeable_cnt == 0);
  				lprops = scan_for_leb_for_idx(c);
  				if (IS_ERR(lprops)) {
  					err = PTR_ERR(lprops);
  					goto out;
  				}
  			}
  		}
  	}
  
  	if (!lprops) {
  		err = -ENOSPC;
  		goto out;
  	}
  
  	lnum = lprops->lnum;
  
  	dbg_find("found LEB %d, free %d, dirty %d, flags %#x",
  		 lnum, lprops->free, lprops->dirty, lprops->flags);
  
  	flags = lprops->flags | LPROPS_TAKEN | LPROPS_INDEX;
  	lprops = ubifs_change_lp(c, lprops, c->leb_size, 0, flags, 0);
  	if (IS_ERR(lprops)) {
  		err = PTR_ERR(lprops);
  		goto out;
  	}
  
  	ubifs_release_lprops(c);
  
  	/*
  	 * Ensure that empty LEBs have been unmapped. They may not have been,
  	 * for example, because of an unclean unmount. Also LEBs that were
  	 * freeable LEBs (free + dirty == leb_size) will not have been unmapped.
  	 */
  	err = ubifs_leb_unmap(c, lnum);
  	if (err) {
  		ubifs_change_one_lp(c, lnum, LPROPS_NC, LPROPS_NC, 0,
  				    LPROPS_TAKEN | LPROPS_INDEX, 0);
  		return err;
  	}
  
  	return lnum;
  
  out:
  	ubifs_release_lprops(c);
  	return err;
  }
  
  static int cmp_dirty_idx(const struct ubifs_lprops **a,
  			 const struct ubifs_lprops **b)
  {
  	const struct ubifs_lprops *lpa = *a;
  	const struct ubifs_lprops *lpb = *b;
  
  	return lpa->dirty + lpa->free - lpb->dirty - lpb->free;
  }
  
  static void swap_dirty_idx(struct ubifs_lprops **a, struct ubifs_lprops **b,
  			   int size)
  {
  	struct ubifs_lprops *t = *a;
  
  	*a = *b;
  	*b = t;
  }
  
  /**
   * ubifs_save_dirty_idx_lnums - save an array of the most dirty index LEB nos.
   * @c: the UBIFS file-system description object
   *
   * This function is called each commit to create an array of LEB numbers of
   * dirty index LEBs sorted in order of dirty and free space.  This is used by
   * the in-the-gaps method of TNC commit.
   */
  int ubifs_save_dirty_idx_lnums(struct ubifs_info *c)
  {
  	int i;
  
  	ubifs_get_lprops(c);
  	/* Copy the LPROPS_DIRTY_IDX heap */
  	c->dirty_idx.cnt = c->lpt_heap[LPROPS_DIRTY_IDX - 1].cnt;
  	memcpy(c->dirty_idx.arr, c->lpt_heap[LPROPS_DIRTY_IDX - 1].arr,
  	       sizeof(void *) * c->dirty_idx.cnt);
  	/* Sort it so that the dirtiest is now at the end */
  	sort(c->dirty_idx.arr, c->dirty_idx.cnt, sizeof(void *),
  	     (int (*)(const void *, const void *))cmp_dirty_idx,
  	     (void (*)(void *, void *, int))swap_dirty_idx);
  	dbg_find("found %d dirty index LEBs", c->dirty_idx.cnt);
  	if (c->dirty_idx.cnt)
  		dbg_find("dirtiest index LEB is %d with dirty %d and free %d",
  			 c->dirty_idx.arr[c->dirty_idx.cnt - 1]->lnum,
  			 c->dirty_idx.arr[c->dirty_idx.cnt - 1]->dirty,
  			 c->dirty_idx.arr[c->dirty_idx.cnt - 1]->free);
  	/* Replace the lprops pointers with LEB numbers */
  	for (i = 0; i < c->dirty_idx.cnt; i++)
  		c->dirty_idx.arr[i] = (void *)(size_t)c->dirty_idx.arr[i]->lnum;
  	ubifs_release_lprops(c);
  	return 0;
  }
  
  /**
   * scan_dirty_idx_cb - callback used by the scan for a dirty index LEB.
   * @c: the UBIFS file-system description object
   * @lprops: LEB properties to scan
   * @in_tree: whether the LEB properties are in main memory
   * @data: information passed to and from the caller of the scan
   *
   * This function returns a code that indicates whether the scan should continue
   * (%LPT_SCAN_CONTINUE), whether the LEB properties should be added to the tree
   * in main memory (%LPT_SCAN_ADD), or whether the scan should stop
   * (%LPT_SCAN_STOP).
   */
  static int scan_dirty_idx_cb(struct ubifs_info *c,
  			   const struct ubifs_lprops *lprops, int in_tree,
  			   struct scan_data *data)
  {
  	int ret = LPT_SCAN_CONTINUE;
  
  	/* Exclude LEBs that are currently in use */
  	if (lprops->flags & LPROPS_TAKEN)
  		return LPT_SCAN_CONTINUE;
  	/* Determine whether to add these LEB properties to the tree */
  	if (!in_tree && valuable(c, lprops))
  		ret |= LPT_SCAN_ADD;
  	/* Exclude non-index LEBs */
  	if (!(lprops->flags & LPROPS_INDEX))
  		return ret;
  	/* Exclude LEBs with too little space */
  	if (lprops->free + lprops->dirty < c->min_idx_node_sz)
  		return ret;
  	/* Finally we found space */
  	data->lnum = lprops->lnum;
  	return LPT_SCAN_ADD | LPT_SCAN_STOP;
  }
  
  /**
   * find_dirty_idx_leb - find a dirty index LEB.
   * @c: the UBIFS file-system description object
   *
   * This function returns LEB number upon success and a negative error code upon
   * failure.  In particular, -ENOSPC is returned if a dirty index LEB is not
   * found.
   *
   * Note that this function scans the entire LPT but it is called very rarely.
   */
  static int find_dirty_idx_leb(struct ubifs_info *c)
  {
  	const struct ubifs_lprops *lprops;
  	struct ubifs_lpt_heap *heap;
  	struct scan_data data;
  	int err, i, ret;
  
  	/* Check all structures in memory first */
  	data.lnum = -1;
  	heap = &c->lpt_heap[LPROPS_DIRTY_IDX - 1];
  	for (i = 0; i < heap->cnt; i++) {
  		lprops = heap->arr[i];
  		ret = scan_dirty_idx_cb(c, lprops, 1, &data);
  		if (ret & LPT_SCAN_STOP)
  			goto found;
  	}
  	list_for_each_entry(lprops, &c->frdi_idx_list, list) {
  		ret = scan_dirty_idx_cb(c, lprops, 1, &data);
  		if (ret & LPT_SCAN_STOP)
  			goto found;
  	}
  	list_for_each_entry(lprops, &c->uncat_list, list) {
  		ret = scan_dirty_idx_cb(c, lprops, 1, &data);
  		if (ret & LPT_SCAN_STOP)
  			goto found;
  	}
  	if (c->pnodes_have >= c->pnode_cnt)
  		/* All pnodes are in memory, so skip scan */
  		return -ENOSPC;
  	err = ubifs_lpt_scan_nolock(c, -1, c->lscan_lnum,
  				    (ubifs_lpt_scan_callback)scan_dirty_idx_cb,
  				    &data);
  	if (err)
  		return err;
  found:
  	ubifs_assert(data.lnum >= c->main_first && data.lnum < c->leb_cnt);
  	c->lscan_lnum = data.lnum;
  	lprops = ubifs_lpt_lookup_dirty(c, data.lnum);
  	if (IS_ERR(lprops))
  		return PTR_ERR(lprops);
  	ubifs_assert(lprops->lnum == data.lnum);
  	ubifs_assert(lprops->free + lprops->dirty >= c->min_idx_node_sz);
  	ubifs_assert(!(lprops->flags & LPROPS_TAKEN));
  	ubifs_assert((lprops->flags & LPROPS_INDEX));
  
  	dbg_find("found dirty LEB %d, free %d, dirty %d, flags %#x",
  		 lprops->lnum, lprops->free, lprops->dirty, lprops->flags);
  
  	lprops = ubifs_change_lp(c, lprops, LPROPS_NC, LPROPS_NC,
  				 lprops->flags | LPROPS_TAKEN, 0);
  	if (IS_ERR(lprops))
  		return PTR_ERR(lprops);
  
  	return lprops->lnum;
  }
  
  /**
   * get_idx_gc_leb - try to get a LEB number from trivial GC.
   * @c: the UBIFS file-system description object
   */
  static int get_idx_gc_leb(struct ubifs_info *c)
  {
  	const struct ubifs_lprops *lp;
  	int err, lnum;
  
  	err = ubifs_get_idx_gc_leb(c);
  	if (err < 0)
  		return err;
  	lnum = err;
  	/*
  	 * The LEB was due to be unmapped after the commit but
  	 * it is needed now for this commit.
  	 */
  	lp = ubifs_lpt_lookup_dirty(c, lnum);
  	if (IS_ERR(lp))
  		return PTR_ERR(lp);
  	lp = ubifs_change_lp(c, lp, LPROPS_NC, LPROPS_NC,
  			     lp->flags | LPROPS_INDEX, -1);
  	if (IS_ERR(lp))
  		return PTR_ERR(lp);
  	dbg_find("LEB %d, dirty %d and free %d flags %#x",
  		 lp->lnum, lp->dirty, lp->free, lp->flags);
  	return lnum;
  }
  
  /**
   * find_dirtiest_idx_leb - find dirtiest index LEB from dirtiest array.
   * @c: the UBIFS file-system description object
   */
  static int find_dirtiest_idx_leb(struct ubifs_info *c)
  {
  	const struct ubifs_lprops *lp;
  	int lnum;
  
  	while (1) {
  		if (!c->dirty_idx.cnt)
  			return -ENOSPC;
  		/* The lprops pointers were replaced by LEB numbers */
  		lnum = (size_t)c->dirty_idx.arr[--c->dirty_idx.cnt];
  		lp = ubifs_lpt_lookup(c, lnum);
  		if (IS_ERR(lp))
  			return PTR_ERR(lp);
  		if ((lp->flags & LPROPS_TAKEN) || !(lp->flags & LPROPS_INDEX))
  			continue;
  		lp = ubifs_change_lp(c, lp, LPROPS_NC, LPROPS_NC,
  				     lp->flags | LPROPS_TAKEN, 0);
  		if (IS_ERR(lp))
  			return PTR_ERR(lp);
  		break;
  	}
  	dbg_find("LEB %d, dirty %d and free %d flags %#x", lp->lnum, lp->dirty,
  		 lp->free, lp->flags);
  	ubifs_assert(lp->flags & LPROPS_TAKEN);
  	ubifs_assert(lp->flags & LPROPS_INDEX);
  	return lnum;
  }
  
  /**
   * ubifs_find_dirty_idx_leb - try to find dirtiest index LEB as at last commit.
   * @c: the UBIFS file-system description object
   *
   * This function attempts to find an untaken index LEB with the most free and
   * dirty space that can be used without overwriting index nodes that were in the
   * last index committed.
   */
  int ubifs_find_dirty_idx_leb(struct ubifs_info *c)
  {
  	int err;
  
  	ubifs_get_lprops(c);
  
  	/*
  	 * We made an array of the dirtiest index LEB numbers as at the start of
  	 * last commit.  Try that array first.
  	 */
  	err = find_dirtiest_idx_leb(c);
  
  	/* Next try scanning the entire LPT */
  	if (err == -ENOSPC)
  		err = find_dirty_idx_leb(c);
  
  	/* Finally take any index LEBs awaiting trivial GC */
  	if (err == -ENOSPC)
  		err = get_idx_gc_leb(c);
  
  	ubifs_release_lprops(c);
  	return err;
  }