Linux 4.2.1

[linux/fpc-iii.git] / fs / ubifs / tnc_commit.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: Adrian Hunter
 *          Artem Bityutskiy (Битюцкий Артём)
 */

/* This file implements TNC functions for committing */

#include <linux/random.h>
#include "ubifs.h"

/**
 * make_idx_node - make an index node for fill-the-gaps method of TNC commit.
 * @c: UBIFS file-system description object
 * @idx: buffer in which to place new index node
 * @znode: znode from which to make new index node
 * @lnum: LEB number where new index node will be written
 * @offs: offset where new index node will be written
 * @len: length of new index node
 */
static int make_idx_node(struct ubifs_info *c, struct ubifs_idx_node *idx,
                         struct ubifs_znode *znode, int lnum, int offs, int len)
{
        struct ubifs_znode *zp;
        int i, err;

        /* Make index node */
        idx->ch.node_type = UBIFS_IDX_NODE;
        idx->child_cnt = cpu_to_le16(znode->child_cnt);
        idx->level = cpu_to_le16(znode->level);
        for (i = 0; i < znode->child_cnt; i++) {
                struct ubifs_branch *br = ubifs_idx_branch(c, idx, i);
                struct ubifs_zbranch *zbr = &znode->zbranch[i];

                key_write_idx(c, &zbr->key, &br->key);
                br->lnum = cpu_to_le32(zbr->lnum);
                br->offs = cpu_to_le32(zbr->offs);
                br->len = cpu_to_le32(zbr->len);
                if (!zbr->lnum || !zbr->len) {
                        ubifs_err(c, "bad ref in znode");
                        ubifs_dump_znode(c, znode);
                        if (zbr->znode)
                                ubifs_dump_znode(c, zbr->znode);
                }
        }
        ubifs_prepare_node(c, idx, len, 0);

        znode->lnum = lnum;
        znode->offs = offs;
        znode->len = len;

        err = insert_old_idx_znode(c, znode);

        /* Update the parent */
        zp = znode->parent;
        if (zp) {
                struct ubifs_zbranch *zbr;

                zbr = &zp->zbranch[znode->iip];
                zbr->lnum = lnum;
                zbr->offs = offs;
                zbr->len = len;
        } else {
                c->zroot.lnum = lnum;
                c->zroot.offs = offs;
                c->zroot.len = len;
        }
        c->calc_idx_sz += ALIGN(len, 8);

        atomic_long_dec(&c->dirty_zn_cnt);

        ubifs_assert(ubifs_zn_dirty(znode));
        ubifs_assert(ubifs_zn_cow(znode));

        /*
         * Note, unlike 'write_index()' we do not add memory barriers here
         * because this function is called with @c->tnc_mutex locked.
         */
        __clear_bit(DIRTY_ZNODE, &znode->flags);
        __clear_bit(COW_ZNODE, &znode->flags);

        return err;
}

/**
 * fill_gap - make index nodes in gaps in dirty index LEBs.
 * @c: UBIFS file-system description object
 * @lnum: LEB number that gap appears in
 * @gap_start: offset of start of gap
 * @gap_end: offset of end of gap
 * @dirt: adds dirty space to this
 *
 * This function returns the number of index nodes written into the gap.
 */
static int fill_gap(struct ubifs_info *c, int lnum, int gap_start, int gap_end,
                    int *dirt)
{
        int len, gap_remains, gap_pos, written, pad_len;

        ubifs_assert((gap_start & 7) == 0);
        ubifs_assert((gap_end & 7) == 0);
        ubifs_assert(gap_end >= gap_start);

        gap_remains = gap_end - gap_start;
        if (!gap_remains)
                return 0;
        gap_pos = gap_start;
        written = 0;
        while (c->enext) {
                len = ubifs_idx_node_sz(c, c->enext->child_cnt);
                if (len < gap_remains) {
                        struct ubifs_znode *znode = c->enext;
                        const int alen = ALIGN(len, 8);
                        int err;

                        ubifs_assert(alen <= gap_remains);
                        err = make_idx_node(c, c->ileb_buf + gap_pos, znode,
                                            lnum, gap_pos, len);
                        if (err)
                                return err;
                        gap_remains -= alen;
                        gap_pos += alen;
                        c->enext = znode->cnext;
                        if (c->enext == c->cnext)
                                c->enext = NULL;
                        written += 1;
                } else
                        break;
        }
        if (gap_end == c->leb_size) {
                c->ileb_len = ALIGN(gap_pos, c->min_io_size);
                /* Pad to end of min_io_size */
                pad_len = c->ileb_len - gap_pos;
        } else
                /* Pad to end of gap */
                pad_len = gap_remains;
        dbg_gc("LEB %d:%d to %d len %d nodes written %d wasted bytes %d",
               lnum, gap_start, gap_end, gap_end - gap_start, written, pad_len);
        ubifs_pad(c, c->ileb_buf + gap_pos, pad_len);
        *dirt += pad_len;
        return written;
}

/**
 * find_old_idx - find an index node obsoleted since the last commit start.
 * @c: UBIFS file-system description object
 * @lnum: LEB number of obsoleted index node
 * @offs: offset of obsoleted index node
 *
 * Returns %1 if found and %0 otherwise.
 */
static int find_old_idx(struct ubifs_info *c, int lnum, int offs)
{
        struct ubifs_old_idx *o;
        struct rb_node *p;

        p = c->old_idx.rb_node;
        while (p) {
                o = rb_entry(p, struct ubifs_old_idx, rb);
                if (lnum < o->lnum)
                        p = p->rb_left;
                else if (lnum > o->lnum)
                        p = p->rb_right;
                else if (offs < o->offs)
                        p = p->rb_left;
                else if (offs > o->offs)
                        p = p->rb_right;
                else
                        return 1;
        }
        return 0;
}

/**
 * is_idx_node_in_use - determine if an index node can be overwritten.
 * @c: UBIFS file-system description object
 * @key: key of index node
 * @level: index node level
 * @lnum: LEB number of index node
 * @offs: offset of index node
 *
 * If @key / @lnum / @offs identify an index node that was not part of the old
 * index, then this function returns %0 (obsolete).  Else if the index node was
 * part of the old index but is now dirty %1 is returned, else if it is clean %2
 * is returned. A negative error code is returned on failure.
 */
static int is_idx_node_in_use(struct ubifs_info *c, union ubifs_key *key,
                              int level, int lnum, int offs)
{
        int ret;

        ret = is_idx_node_in_tnc(c, key, level, lnum, offs);
        if (ret < 0)
                return ret; /* Error code */
        if (ret == 0)
                if (find_old_idx(c, lnum, offs))
                        return 1;
        return ret;
}

/**
 * layout_leb_in_gaps - layout index nodes using in-the-gaps method.
 * @c: UBIFS file-system description object
 * @p: return LEB number here
 *
 * This function lays out new index nodes for dirty znodes using in-the-gaps
 * method of TNC commit.
 * This function merely puts the next znode into the next gap, making no attempt
 * to try to maximise the number of znodes that fit.
 * This function returns the number of index nodes written into the gaps, or a
 * negative error code on failure.
 */
static int layout_leb_in_gaps(struct ubifs_info *c, int *p)
{
        struct ubifs_scan_leb *sleb;
        struct ubifs_scan_node *snod;
        int lnum, dirt = 0, gap_start, gap_end, err, written, tot_written;

        tot_written = 0;
        /* Get an index LEB with lots of obsolete index nodes */
        lnum = ubifs_find_dirty_idx_leb(c);
        if (lnum < 0)
                /*
                 * There also may be dirt in the index head that could be
                 * filled, however we do not check there at present.
                 */
                return lnum; /* Error code */
        *p = lnum;
        dbg_gc("LEB %d", lnum);
        /*
         * Scan the index LEB.  We use the generic scan for this even though
         * it is more comprehensive and less efficient than is needed for this
         * purpose.
         */
        sleb = ubifs_scan(c, lnum, 0, c->ileb_buf, 0);
        c->ileb_len = 0;
        if (IS_ERR(sleb))
                return PTR_ERR(sleb);
        gap_start = 0;
        list_for_each_entry(snod, &sleb->nodes, list) {
                struct ubifs_idx_node *idx;
                int in_use, level;

                ubifs_assert(snod->type == UBIFS_IDX_NODE);
                idx = snod->node;
                key_read(c, ubifs_idx_key(c, idx), &snod->key);
                level = le16_to_cpu(idx->level);
                /* Determine if the index node is in use (not obsolete) */
                in_use = is_idx_node_in_use(c, &snod->key, level, lnum,
                                            snod->offs);
                if (in_use < 0) {
                        ubifs_scan_destroy(sleb);
                        return in_use; /* Error code */
                }
                if (in_use) {
                        if (in_use == 1)
                                dirt += ALIGN(snod->len, 8);
                        /*
                         * The obsolete index nodes form gaps that can be
                         * overwritten.  This gap has ended because we have
                         * found an index node that is still in use
                         * i.e. not obsolete
                         */
                        gap_end = snod->offs;
                        /* Try to fill gap */
                        written = fill_gap(c, lnum, gap_start, gap_end, &dirt);
                        if (written < 0) {
                                ubifs_scan_destroy(sleb);
                                return written; /* Error code */
                        }
                        tot_written += written;
                        gap_start = ALIGN(snod->offs + snod->len, 8);
                }
        }
        ubifs_scan_destroy(sleb);
        c->ileb_len = c->leb_size;
        gap_end = c->leb_size;
        /* Try to fill gap */
        written = fill_gap(c, lnum, gap_start, gap_end, &dirt);
        if (written < 0)
                return written; /* Error code */
        tot_written += written;
        if (tot_written == 0) {
                struct ubifs_lprops lp;

                dbg_gc("LEB %d wrote %d index nodes", lnum, tot_written);
                err = ubifs_read_one_lp(c, lnum, &lp);
                if (err)
                        return err;
                if (lp.free == c->leb_size) {
                        /*
                         * We must have snatched this LEB from the idx_gc list
                         * so we need to correct the free and dirty space.
                         */
                        err = ubifs_change_one_lp(c, lnum,
                                                  c->leb_size - c->ileb_len,
                                                  dirt, 0, 0, 0);
                        if (err)
                                return err;
                }
                return 0;
        }
        err = ubifs_change_one_lp(c, lnum, c->leb_size - c->ileb_len, dirt,
                                  0, 0, 0);
        if (err)
                return err;
        err = ubifs_leb_change(c, lnum, c->ileb_buf, c->ileb_len);
        if (err)
                return err;
        dbg_gc("LEB %d wrote %d index nodes", lnum, tot_written);
        return tot_written;
}

/**
 * get_leb_cnt - calculate the number of empty LEBs needed to commit.
 * @c: UBIFS file-system description object
 * @cnt: number of znodes to commit
 *
 * This function returns the number of empty LEBs needed to commit @cnt znodes
 * to the current index head.  The number is not exact and may be more than
 * needed.
 */
static int get_leb_cnt(struct ubifs_info *c, int cnt)
{
        int d;

        /* Assume maximum index node size (i.e. overestimate space needed) */
        cnt -= (c->leb_size - c->ihead_offs) / c->max_idx_node_sz;
        if (cnt < 0)
                cnt = 0;
        d = c->leb_size / c->max_idx_node_sz;
        return DIV_ROUND_UP(cnt, d);
}

/**
 * layout_in_gaps - in-the-gaps method of committing TNC.
 * @c: UBIFS file-system description object
 * @cnt: number of dirty znodes to commit.
 *
 * This function lays out new index nodes for dirty znodes using in-the-gaps
 * method of TNC commit.
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int layout_in_gaps(struct ubifs_info *c, int cnt)
{
        int err, leb_needed_cnt, written, *p;

        dbg_gc("%d znodes to write", cnt);

        c->gap_lebs = kmalloc(sizeof(int) * (c->lst.idx_lebs + 1), GFP_NOFS);
        if (!c->gap_lebs)
                return -ENOMEM;

        p = c->gap_lebs;
        do {
                ubifs_assert(p < c->gap_lebs + sizeof(int) * c->lst.idx_lebs);
                written = layout_leb_in_gaps(c, p);
                if (written < 0) {
                        err = written;
                        if (err != -ENOSPC) {
                                kfree(c->gap_lebs);
                                c->gap_lebs = NULL;
                                return err;
                        }
                        if (!dbg_is_chk_index(c)) {
                                /*
                                 * Do not print scary warnings if the debugging
                                 * option which forces in-the-gaps is enabled.
                                 */
                                ubifs_warn(c, "out of space");
                                ubifs_dump_budg(c, &c->bi);
                                ubifs_dump_lprops(c);
                        }
                        /* Try to commit anyway */
                        break;
                }
                p++;
                cnt -= written;
                leb_needed_cnt = get_leb_cnt(c, cnt);
                dbg_gc("%d znodes remaining, need %d LEBs, have %d", cnt,
                       leb_needed_cnt, c->ileb_cnt);
        } while (leb_needed_cnt > c->ileb_cnt);

        *p = -1;
        return 0;
}

/**
 * layout_in_empty_space - layout index nodes in empty space.
 * @c: UBIFS file-system description object
 *
 * This function lays out new index nodes for dirty znodes using empty LEBs.
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int layout_in_empty_space(struct ubifs_info *c)
{
        struct ubifs_znode *znode, *cnext, *zp;
        int lnum, offs, len, next_len, buf_len, buf_offs, used, avail;
        int wlen, blen, err;

        cnext = c->enext;
        if (!cnext)
                return 0;

        lnum = c->ihead_lnum;
        buf_offs = c->ihead_offs;

        buf_len = ubifs_idx_node_sz(c, c->fanout);
        buf_len = ALIGN(buf_len, c->min_io_size);
        used = 0;
        avail = buf_len;

        /* Ensure there is enough room for first write */
        next_len = ubifs_idx_node_sz(c, cnext->child_cnt);
        if (buf_offs + next_len > c->leb_size)
                lnum = -1;

        while (1) {
                znode = cnext;

                len = ubifs_idx_node_sz(c, znode->child_cnt);

                /* Determine the index node position */
                if (lnum == -1) {
                        if (c->ileb_nxt >= c->ileb_cnt) {
                                ubifs_err(c, "out of space");
                                return -ENOSPC;
                        }
                        lnum = c->ilebs[c->ileb_nxt++];
                        buf_offs = 0;
                        used = 0;
                        avail = buf_len;
                }

                offs = buf_offs + used;

                znode->lnum = lnum;
                znode->offs = offs;
                znode->len = len;

                /* Update the parent */
                zp = znode->parent;
                if (zp) {
                        struct ubifs_zbranch *zbr;
                        int i;

                        i = znode->iip;
                        zbr = &zp->zbranch[i];
                        zbr->lnum = lnum;
                        zbr->offs = offs;
                        zbr->len = len;
                } else {
                        c->zroot.lnum = lnum;
                        c->zroot.offs = offs;
                        c->zroot.len = len;
                }
                c->calc_idx_sz += ALIGN(len, 8);

                /*
                 * Once lprops is updated, we can decrease the dirty znode count
                 * but it is easier to just do it here.
                 */
                atomic_long_dec(&c->dirty_zn_cnt);

                /*
                 * Calculate the next index node length to see if there is
                 * enough room for it
                 */
                cnext = znode->cnext;
                if (cnext == c->cnext)
                        next_len = 0;
                else
                        next_len = ubifs_idx_node_sz(c, cnext->child_cnt);

                /* Update buffer positions */
                wlen = used + len;
                used += ALIGN(len, 8);
                avail -= ALIGN(len, 8);

                if (next_len != 0 &&
                    buf_offs + used + next_len <= c->leb_size &&
                    avail > 0)
                        continue;

                if (avail <= 0 && next_len &&
                    buf_offs + used + next_len <= c->leb_size)
                        blen = buf_len;
                else
                        blen = ALIGN(wlen, c->min_io_size);

                /* The buffer is full or there are no more znodes to do */
                buf_offs += blen;
                if (next_len) {
                        if (buf_offs + next_len > c->leb_size) {
                                err = ubifs_update_one_lp(c, lnum,
                                        c->leb_size - buf_offs, blen - used,
                                        0, 0);
                                if (err)
                                        return err;
                                lnum = -1;
                        }
                        used -= blen;
                        if (used < 0)
                                used = 0;
                        avail = buf_len - used;
                        continue;
                }
                err = ubifs_update_one_lp(c, lnum, c->leb_size - buf_offs,
                                          blen - used, 0, 0);
                if (err)
                        return err;
                break;
        }

        c->dbg->new_ihead_lnum = lnum;
        c->dbg->new_ihead_offs = buf_offs;

        return 0;
}

/**
 * layout_commit - determine positions of index nodes to commit.
 * @c: UBIFS file-system description object
 * @no_space: indicates that insufficient empty LEBs were allocated
 * @cnt: number of znodes to commit
 *
 * Calculate and update the positions of index nodes to commit.  If there were
 * an insufficient number of empty LEBs allocated, then index nodes are placed
 * into the gaps created by obsolete index nodes in non-empty index LEBs.  For
 * this purpose, an obsolete index node is one that was not in the index as at
 * the end of the last commit.  To write "in-the-gaps" requires that those index
 * LEBs are updated atomically in-place.
 */
static int layout_commit(struct ubifs_info *c, int no_space, int cnt)
{
        int err;

        if (no_space) {
                err = layout_in_gaps(c, cnt);
                if (err)
                        return err;
        }
        err = layout_in_empty_space(c);
        return err;
}

/**
 * find_first_dirty - find first dirty znode.
 * @znode: znode to begin searching from
 */
static struct ubifs_znode *find_first_dirty(struct ubifs_znode *znode)
{
        int i, cont;

        if (!znode)
                return NULL;

        while (1) {
                if (znode->level == 0) {
                        if (ubifs_zn_dirty(znode))
                                return znode;
                        return NULL;
                }
                cont = 0;
                for (i = 0; i < znode->child_cnt; i++) {
                        struct ubifs_zbranch *zbr = &znode->zbranch[i];

                        if (zbr->znode && ubifs_zn_dirty(zbr->znode)) {
                                znode = zbr->znode;
                                cont = 1;
                                break;
                        }
                }
                if (!cont) {
                        if (ubifs_zn_dirty(znode))
                                return znode;
                        return NULL;
                }
        }
}

/**
 * find_next_dirty - find next dirty znode.
 * @znode: znode to begin searching from
 */
static struct ubifs_znode *find_next_dirty(struct ubifs_znode *znode)
{
        int n = znode->iip + 1;

        znode = znode->parent;
        if (!znode)
                return NULL;
        for (; n < znode->child_cnt; n++) {
                struct ubifs_zbranch *zbr = &znode->zbranch[n];

                if (zbr->znode && ubifs_zn_dirty(zbr->znode))
                        return find_first_dirty(zbr->znode);
        }
        return znode;
}

/**
 * get_znodes_to_commit - create list of dirty znodes to commit.
 * @c: UBIFS file-system description object
 *
 * This function returns the number of znodes to commit.
 */
static int get_znodes_to_commit(struct ubifs_info *c)
{
        struct ubifs_znode *znode, *cnext;
        int cnt = 0;

        c->cnext = find_first_dirty(c->zroot.znode);
        znode = c->enext = c->cnext;
        if (!znode) {
                dbg_cmt("no znodes to commit");
                return 0;
        }
        cnt += 1;
        while (1) {
                ubifs_assert(!ubifs_zn_cow(znode));
                __set_bit(COW_ZNODE, &znode->flags);
                znode->alt = 0;
                cnext = find_next_dirty(znode);
                if (!cnext) {
                        znode->cnext = c->cnext;
                        break;
                }
                znode->cnext = cnext;
                znode = cnext;
                cnt += 1;
        }
        dbg_cmt("committing %d znodes", cnt);
        ubifs_assert(cnt == atomic_long_read(&c->dirty_zn_cnt));
        return cnt;
}

/**
 * alloc_idx_lebs - allocate empty LEBs to be used to commit.
 * @c: UBIFS file-system description object
 * @cnt: number of znodes to commit
 *
 * This function returns %-ENOSPC if it cannot allocate a sufficient number of
 * empty LEBs.  %0 is returned on success, otherwise a negative error code
 * is returned.
 */
static int alloc_idx_lebs(struct ubifs_info *c, int cnt)
{
        int i, leb_cnt, lnum;

        c->ileb_cnt = 0;
        c->ileb_nxt = 0;
        leb_cnt = get_leb_cnt(c, cnt);
        dbg_cmt("need about %d empty LEBS for TNC commit", leb_cnt);
        if (!leb_cnt)
                return 0;
        c->ilebs = kmalloc(leb_cnt * sizeof(int), GFP_NOFS);
        if (!c->ilebs)
                return -ENOMEM;
        for (i = 0; i < leb_cnt; i++) {
                lnum = ubifs_find_free_leb_for_idx(c);
                if (lnum < 0)
                        return lnum;
                c->ilebs[c->ileb_cnt++] = lnum;
                dbg_cmt("LEB %d", lnum);
        }
        if (dbg_is_chk_index(c) && !(prandom_u32() & 7))
                return -ENOSPC;
        return 0;
}

/**
 * free_unused_idx_lebs - free unused LEBs that were allocated for the commit.
 * @c: UBIFS file-system description object
 *
 * It is possible that we allocate more empty LEBs for the commit than we need.
 * This functions frees the surplus.
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int free_unused_idx_lebs(struct ubifs_info *c)
{
        int i, err = 0, lnum, er;

        for (i = c->ileb_nxt; i < c->ileb_cnt; i++) {
                lnum = c->ilebs[i];
                dbg_cmt("LEB %d", lnum);
                er = ubifs_change_one_lp(c, lnum, LPROPS_NC, LPROPS_NC, 0,
                                         LPROPS_INDEX | LPROPS_TAKEN, 0);
                if (!err)
                        err = er;
        }
        return err;
}

/**
 * free_idx_lebs - free unused LEBs after commit end.
 * @c: UBIFS file-system description object
 *
 * This function returns %0 on success and a negative error code on failure.
 */
static int free_idx_lebs(struct ubifs_info *c)
{
        int err;

        err = free_unused_idx_lebs(c);
        kfree(c->ilebs);
        c->ilebs = NULL;
        return err;
}

/**
 * ubifs_tnc_start_commit - start TNC commit.
 * @c: UBIFS file-system description object
 * @zroot: new index root position is returned here
 *
 * This function prepares the list of indexing nodes to commit and lays out
 * their positions on flash. If there is not enough free space it uses the
 * in-gap commit method. Returns zero in case of success and a negative error
 * code in case of failure.
 */
int ubifs_tnc_start_commit(struct ubifs_info *c, struct ubifs_zbranch *zroot)
{
        int err = 0, cnt;

        mutex_lock(&c->tnc_mutex);
        err = dbg_check_tnc(c, 1);
        if (err)
                goto out;
        cnt = get_znodes_to_commit(c);
        if (cnt != 0) {
                int no_space = 0;

                err = alloc_idx_lebs(c, cnt);
                if (err == -ENOSPC)
                        no_space = 1;
                else if (err)
                        goto out_free;
                err = layout_commit(c, no_space, cnt);
                if (err)
                        goto out_free;
                ubifs_assert(atomic_long_read(&c->dirty_zn_cnt) == 0);
                err = free_unused_idx_lebs(c);
                if (err)
                        goto out;
        }
        destroy_old_idx(c);
        memcpy(zroot, &c->zroot, sizeof(struct ubifs_zbranch));

        err = ubifs_save_dirty_idx_lnums(c);
        if (err)
                goto out;

        spin_lock(&c->space_lock);
        /*
         * Although we have not finished committing yet, update size of the
         * committed index ('c->bi.old_idx_sz') and zero out the index growth
         * budget. It is OK to do this now, because we've reserved all the
         * space which is needed to commit the index, and it is save for the
         * budgeting subsystem to assume the index is already committed,
         * even though it is not.
         */
        ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
        c->bi.old_idx_sz = c->calc_idx_sz;
        c->bi.uncommitted_idx = 0;
        c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
        spin_unlock(&c->space_lock);
        mutex_unlock(&c->tnc_mutex);

        dbg_cmt("number of index LEBs %d", c->lst.idx_lebs);
        dbg_cmt("size of index %llu", c->calc_idx_sz);
        return err;

out_free:
        free_idx_lebs(c);
out:
        mutex_unlock(&c->tnc_mutex);
        return err;
}

/**
 * write_index - write index nodes.
 * @c: UBIFS file-system description object
 *
 * This function writes the index nodes whose positions were laid out in the
 * layout_in_empty_space function.
 */
static int write_index(struct ubifs_info *c)
{
        struct ubifs_idx_node *idx;
        struct ubifs_znode *znode, *cnext;
        int i, lnum, offs, len, next_len, buf_len, buf_offs, used;
        int avail, wlen, err, lnum_pos = 0, blen, nxt_offs;

        cnext = c->enext;
        if (!cnext)
                return 0;

        /*
         * Always write index nodes to the index head so that index nodes and
         * other types of nodes are never mixed in the same erase block.
         */
        lnum = c->ihead_lnum;
        buf_offs = c->ihead_offs;

        /* Allocate commit buffer */
        buf_len = ALIGN(c->max_idx_node_sz, c->min_io_size);
        used = 0;
        avail = buf_len;

        /* Ensure there is enough room for first write */
        next_len = ubifs_idx_node_sz(c, cnext->child_cnt);
        if (buf_offs + next_len > c->leb_size) {
                err = ubifs_update_one_lp(c, lnum, LPROPS_NC, 0, 0,
                                          LPROPS_TAKEN);
                if (err)
                        return err;
                lnum = -1;
        }

        while (1) {
                cond_resched();

                znode = cnext;
                idx = c->cbuf + used;

                /* Make index node */
                idx->ch.node_type = UBIFS_IDX_NODE;
                idx->child_cnt = cpu_to_le16(znode->child_cnt);
                idx->level = cpu_to_le16(znode->level);
                for (i = 0; i < znode->child_cnt; i++) {
                        struct ubifs_branch *br = ubifs_idx_branch(c, idx, i);
                        struct ubifs_zbranch *zbr = &znode->zbranch[i];

                        key_write_idx(c, &zbr->key, &br->key);
                        br->lnum = cpu_to_le32(zbr->lnum);
                        br->offs = cpu_to_le32(zbr->offs);
                        br->len = cpu_to_le32(zbr->len);
                        if (!zbr->lnum || !zbr->len) {
                                ubifs_err(c, "bad ref in znode");
                                ubifs_dump_znode(c, znode);
                                if (zbr->znode)
                                        ubifs_dump_znode(c, zbr->znode);
                        }
                }
                len = ubifs_idx_node_sz(c, znode->child_cnt);
                ubifs_prepare_node(c, idx, len, 0);

                /* Determine the index node position */
                if (lnum == -1) {
                        lnum = c->ilebs[lnum_pos++];
                        buf_offs = 0;
                        used = 0;
                        avail = buf_len;
                }
                offs = buf_offs + used;

                if (lnum != znode->lnum || offs != znode->offs ||
                    len != znode->len) {
                        ubifs_err(c, "inconsistent znode posn");
                        return -EINVAL;
                }

                /* Grab some stuff from znode while we still can */
                cnext = znode->cnext;

                ubifs_assert(ubifs_zn_dirty(znode));
                ubifs_assert(ubifs_zn_cow(znode));

                /*
                 * It is important that other threads should see %DIRTY_ZNODE
                 * flag cleared before %COW_ZNODE. Specifically, it matters in
                 * the 'dirty_cow_znode()' function. This is the reason for the
                 * first barrier. Also, we want the bit changes to be seen to
                 * other threads ASAP, to avoid unnecesarry copying, which is
                 * the reason for the second barrier.
                 */
                clear_bit(DIRTY_ZNODE, &znode->flags);
                smp_mb__before_atomic();
                clear_bit(COW_ZNODE, &znode->flags);
                smp_mb__after_atomic();

                /*
                 * We have marked the znode as clean but have not updated the
                 * @c->clean_zn_cnt counter. If this znode becomes dirty again
                 * before 'free_obsolete_znodes()' is called, then
                 * @c->clean_zn_cnt will be decremented before it gets
                 * incremented (resulting in 2 decrements for the same znode).
                 * This means that @c->clean_zn_cnt may become negative for a
                 * while.
                 *
                 * Q: why we cannot increment @c->clean_zn_cnt?
                 * A: because we do not have the @c->tnc_mutex locked, and the
                 *    following code would be racy and buggy:
                 *
                 *    if (!ubifs_zn_obsolete(znode)) {
                 *            atomic_long_inc(&c->clean_zn_cnt);
                 *            atomic_long_inc(&ubifs_clean_zn_cnt);
                 *    }
                 *
                 *    Thus, we just delay the @c->clean_zn_cnt update until we
                 *    have the mutex locked.
                 */

                /* Do not access znode from this point on */

                /* Update buffer positions */
                wlen = used + len;
                used += ALIGN(len, 8);
                avail -= ALIGN(len, 8);

                /*
                 * Calculate the next index node length to see if there is
                 * enough room for it
                 */
                if (cnext == c->cnext)
                        next_len = 0;
                else
                        next_len = ubifs_idx_node_sz(c, cnext->child_cnt);

                nxt_offs = buf_offs + used + next_len;
                if (next_len && nxt_offs <= c->leb_size) {
                        if (avail > 0)
                                continue;
                        else
                                blen = buf_len;
                } else {
                        wlen = ALIGN(wlen, 8);
                        blen = ALIGN(wlen, c->min_io_size);
                        ubifs_pad(c, c->cbuf + wlen, blen - wlen);
                }

                /* The buffer is full or there are no more znodes to do */
                err = ubifs_leb_write(c, lnum, c->cbuf, buf_offs, blen);
                if (err)
                        return err;
                buf_offs += blen;
                if (next_len) {
                        if (nxt_offs > c->leb_size) {
                                err = ubifs_update_one_lp(c, lnum, LPROPS_NC, 0,
                                                          0, LPROPS_TAKEN);
                                if (err)
                                        return err;
                                lnum = -1;
                        }
                        used -= blen;
                        if (used < 0)
                                used = 0;
                        avail = buf_len - used;
                        memmove(c->cbuf, c->cbuf + blen, used);
                        continue;
                }
                break;
        }

        if (lnum != c->dbg->new_ihead_lnum ||
            buf_offs != c->dbg->new_ihead_offs) {
                ubifs_err(c, "inconsistent ihead");
                return -EINVAL;
        }

        c->ihead_lnum = lnum;
        c->ihead_offs = buf_offs;

        return 0;
}

/**
 * free_obsolete_znodes - free obsolete znodes.
 * @c: UBIFS file-system description object
 *
 * At the end of commit end, obsolete znodes are freed.
 */
static void free_obsolete_znodes(struct ubifs_info *c)
{
        struct ubifs_znode *znode, *cnext;

        cnext = c->cnext;
        do {
                znode = cnext;
                cnext = znode->cnext;
                if (ubifs_zn_obsolete(znode))
                        kfree(znode);
                else {
                        znode->cnext = NULL;
                        atomic_long_inc(&c->clean_zn_cnt);
                        atomic_long_inc(&ubifs_clean_zn_cnt);
                }
        } while (cnext != c->cnext);
}

/**
 * return_gap_lebs - return LEBs used by the in-gap commit method.
 * @c: UBIFS file-system description object
 *
 * This function clears the "taken" flag for the LEBs which were used by the
 * "commit in-the-gaps" method.
 */
static int return_gap_lebs(struct ubifs_info *c)
{
        int *p, err;

        if (!c->gap_lebs)
                return 0;

        dbg_cmt("");
        for (p = c->gap_lebs; *p != -1; p++) {
                err = ubifs_change_one_lp(c, *p, LPROPS_NC, LPROPS_NC, 0,
                                          LPROPS_TAKEN, 0);
                if (err)
                        return err;
        }

        kfree(c->gap_lebs);
        c->gap_lebs = NULL;
        return 0;
}

/**
 * ubifs_tnc_end_commit - update the TNC for commit end.
 * @c: UBIFS file-system description object
 *
 * Write the dirty znodes.
 */
int ubifs_tnc_end_commit(struct ubifs_info *c)
{
        int err;

        if (!c->cnext)
                return 0;

        err = return_gap_lebs(c);
        if (err)
                return err;

        err = write_index(c);
        if (err)
                return err;

        mutex_lock(&c->tnc_mutex);

        dbg_cmt("TNC height is %d", c->zroot.znode->level + 1);

        free_obsolete_znodes(c);

        c->cnext = NULL;
        kfree(c->ilebs);
        c->ilebs = NULL;

        mutex_unlock(&c->tnc_mutex);

        return 0;
}