Merge branch 'linus' into x86/paravirt-spinlocks

[linux-2.6] / fs / ubifs / find.c

/*
 * 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:
 *   o LEBs which have less than dead watermark of dirty space are never picked
 *   by 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".
 *
 * 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.
 */
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;
                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->min_idx_lebs >= c->lst.idx_lebs) {
                        rsvd_idx_lebs = c->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->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 twice as more space for the index than it
                 * actually takes, it does not make sense to pick indexing LEBs
                 * with less than half LEB of dirty space.
                 */
                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->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
 * @free: contains amount of free space in the LEB 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 *free,
                          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->min_idx_lebs > c->lst.idx_lebs)
                rsvd_idx_lebs = c->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;
        ubifs_assert(lebs + c->lst.idx_lebs >= c->min_idx_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);
        }

        *free = lprops->free;
        ubifs_release_lprops(c);

        if (*free == c->leb_size) {
                /*
                 * 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, *free);
        ubifs_assert(*free >= 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) {
                        ubifs_assert(c->freeable_cnt == 0);
                        if (c->lst.empty_lebs - c->lst.taken_empty_lebs > 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 (unlikely(IS_ERR(lp)))
                return PTR_ERR(lp);
        lp = ubifs_change_lp(c, lp, LPROPS_NC, LPROPS_NC,
                             lp->flags | LPROPS_INDEX, -1);
        if (unlikely(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;
}