[linux-2.6-omap-h63xx.git] / fs / ext4 / extents.c

/*
 * Copyright (c) 2003-2006, Cluster File Systems, Inc, info@clusterfs.com
 * Written by Alex Tomas <alex@clusterfs.com>
 *
 * Architecture independence:
 *   Copyright (c) 2005, Bull S.A.
 *   Written by Pierre Peiffer <pierre.peiffer@bull.net>
 *
 * 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 Licens
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-
 */

/*
 * Extents support for EXT4
 *
 * TODO:
 *   - ext4*_error() should be used in some situations
 *   - analyze all BUG()/BUG_ON(), use -EIO where appropriate
 *   - smart tree reduction
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/time.h>
#include <linux/ext4_jbd2.h>
#include <linux/jbd2.h>
#include <linux/highuid.h>
#include <linux/pagemap.h>
#include <linux/quotaops.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/falloc.h>
#include <linux/ext4_fs_extents.h>
#include <asm/uaccess.h>


/*
 * ext_pblock:
 * combine low and high parts of physical block number into ext4_fsblk_t
 */
static ext4_fsblk_t ext_pblock(struct ext4_extent *ex)
{
        ext4_fsblk_t block;

        block = le32_to_cpu(ex->ee_start_lo);
        block |= ((ext4_fsblk_t) le16_to_cpu(ex->ee_start_hi) << 31) << 1;
        return block;
}

/*
 * idx_pblock:
 * combine low and high parts of a leaf physical block number into ext4_fsblk_t
 */
static ext4_fsblk_t idx_pblock(struct ext4_extent_idx *ix)
{
        ext4_fsblk_t block;

        block = le32_to_cpu(ix->ei_leaf_lo);
        block |= ((ext4_fsblk_t) le16_to_cpu(ix->ei_leaf_hi) << 31) << 1;
        return block;
}

/*
 * ext4_ext_store_pblock:
 * stores a large physical block number into an extent struct,
 * breaking it into parts
 */
static void ext4_ext_store_pblock(struct ext4_extent *ex, ext4_fsblk_t pb)
{
        ex->ee_start_lo = cpu_to_le32((unsigned long) (pb & 0xffffffff));
        ex->ee_start_hi = cpu_to_le16((unsigned long) ((pb >> 31) >> 1) & 0xffff);
}

/*
 * ext4_idx_store_pblock:
 * stores a large physical block number into an index struct,
 * breaking it into parts
 */
static void ext4_idx_store_pblock(struct ext4_extent_idx *ix, ext4_fsblk_t pb)
{
        ix->ei_leaf_lo = cpu_to_le32((unsigned long) (pb & 0xffffffff));
        ix->ei_leaf_hi = cpu_to_le16((unsigned long) ((pb >> 31) >> 1) & 0xffff);
}

static handle_t *ext4_ext_journal_restart(handle_t *handle, int needed)
{
        int err;

        if (handle->h_buffer_credits > needed)
                return handle;
        if (!ext4_journal_extend(handle, needed))
                return handle;
        err = ext4_journal_restart(handle, needed);

        return handle;
}

/*
 * could return:
 *  - EROFS
 *  - ENOMEM
 */
static int ext4_ext_get_access(handle_t *handle, struct inode *inode,
                                struct ext4_ext_path *path)
{
        if (path->p_bh) {
                /* path points to block */
                return ext4_journal_get_write_access(handle, path->p_bh);
        }
        /* path points to leaf/index in inode body */
        /* we use in-core data, no need to protect them */
        return 0;
}

/*
 * could return:
 *  - EROFS
 *  - ENOMEM
 *  - EIO
 */
static int ext4_ext_dirty(handle_t *handle, struct inode *inode,
                                struct ext4_ext_path *path)
{
        int err;
        if (path->p_bh) {
                /* path points to block */
                err = ext4_journal_dirty_metadata(handle, path->p_bh);
        } else {
                /* path points to leaf/index in inode body */
                err = ext4_mark_inode_dirty(handle, inode);
        }
        return err;
}

static ext4_fsblk_t ext4_ext_find_goal(struct inode *inode,
                              struct ext4_ext_path *path,
                              ext4_lblk_t block)
{
        struct ext4_inode_info *ei = EXT4_I(inode);
        ext4_fsblk_t bg_start;
        ext4_grpblk_t colour;
        int depth;

        if (path) {
                struct ext4_extent *ex;
                depth = path->p_depth;

                /* try to predict block placement */
                ex = path[depth].p_ext;
                if (ex)
                        return ext_pblock(ex)+(block-le32_to_cpu(ex->ee_block));

                /* it looks like index is empty;
                 * try to find starting block from index itself */
                if (path[depth].p_bh)
                        return path[depth].p_bh->b_blocknr;
        }

        /* OK. use inode's group */
        bg_start = (ei->i_block_group * EXT4_BLOCKS_PER_GROUP(inode->i_sb)) +
                le32_to_cpu(EXT4_SB(inode->i_sb)->s_es->s_first_data_block);
        colour = (current->pid % 16) *
                        (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
        return bg_start + colour + block;
}

static ext4_fsblk_t
ext4_ext_new_block(handle_t *handle, struct inode *inode,
                        struct ext4_ext_path *path,
                        struct ext4_extent *ex, int *err)
{
        ext4_fsblk_t goal, newblock;

        goal = ext4_ext_find_goal(inode, path, le32_to_cpu(ex->ee_block));
        newblock = ext4_new_block(handle, inode, goal, err);
        return newblock;
}

static int ext4_ext_space_block(struct inode *inode)
{
        int size;

        size = (inode->i_sb->s_blocksize - sizeof(struct ext4_extent_header))
                        / sizeof(struct ext4_extent);
#ifdef AGGRESSIVE_TEST
        if (size > 6)
                size = 6;
#endif
        return size;
}

static int ext4_ext_space_block_idx(struct inode *inode)
{
        int size;

        size = (inode->i_sb->s_blocksize - sizeof(struct ext4_extent_header))
                        / sizeof(struct ext4_extent_idx);
#ifdef AGGRESSIVE_TEST
        if (size > 5)
                size = 5;
#endif
        return size;
}

static int ext4_ext_space_root(struct inode *inode)
{
        int size;

        size = sizeof(EXT4_I(inode)->i_data);
        size -= sizeof(struct ext4_extent_header);
        size /= sizeof(struct ext4_extent);
#ifdef AGGRESSIVE_TEST
        if (size > 3)
                size = 3;
#endif
        return size;
}

static int ext4_ext_space_root_idx(struct inode *inode)
{
        int size;

        size = sizeof(EXT4_I(inode)->i_data);
        size -= sizeof(struct ext4_extent_header);
        size /= sizeof(struct ext4_extent_idx);
#ifdef AGGRESSIVE_TEST
        if (size > 4)
                size = 4;
#endif
        return size;
}

static int
ext4_ext_max_entries(struct inode *inode, int depth)
{
        int max;

        if (depth == ext_depth(inode)) {
                if (depth == 0)
                        max = ext4_ext_space_root(inode);
                else
                        max = ext4_ext_space_root_idx(inode);
        } else {
                if (depth == 0)
                        max = ext4_ext_space_block(inode);
                else
                        max = ext4_ext_space_block_idx(inode);
        }

        return max;
}

static int __ext4_ext_check_header(const char *function, struct inode *inode,
                                        struct ext4_extent_header *eh,
                                        int depth)
{
        const char *error_msg;
        int max = 0;

        if (unlikely(eh->eh_magic != EXT4_EXT_MAGIC)) {
                error_msg = "invalid magic";
                goto corrupted;
        }
        if (unlikely(le16_to_cpu(eh->eh_depth) != depth)) {
                error_msg = "unexpected eh_depth";
                goto corrupted;
        }
        if (unlikely(eh->eh_max == 0)) {
                error_msg = "invalid eh_max";
                goto corrupted;
        }
        max = ext4_ext_max_entries(inode, depth);
        if (unlikely(le16_to_cpu(eh->eh_max) > max)) {
                error_msg = "too large eh_max";
                goto corrupted;
        }
        if (unlikely(le16_to_cpu(eh->eh_entries) > le16_to_cpu(eh->eh_max))) {
                error_msg = "invalid eh_entries";
                goto corrupted;
        }
        return 0;

corrupted:
        ext4_error(inode->i_sb, function,
                        "bad header in inode #%lu: %s - magic %x, "
                        "entries %u, max %u(%u), depth %u(%u)",
                        inode->i_ino, error_msg, le16_to_cpu(eh->eh_magic),
                        le16_to_cpu(eh->eh_entries), le16_to_cpu(eh->eh_max),
                        max, le16_to_cpu(eh->eh_depth), depth);

        return -EIO;
}

#define ext4_ext_check_header(inode, eh, depth) \
        __ext4_ext_check_header(__FUNCTION__, inode, eh, depth)

#ifdef EXT_DEBUG
static void ext4_ext_show_path(struct inode *inode, struct ext4_ext_path *path)
{
        int k, l = path->p_depth;

        ext_debug("path:");
        for (k = 0; k <= l; k++, path++) {
                if (path->p_idx) {
                  ext_debug("  %d->%llu", le32_to_cpu(path->p_idx->ei_block),
                            idx_pblock(path->p_idx));
                } else if (path->p_ext) {
                        ext_debug("  %d:%d:%llu ",
                                  le32_to_cpu(path->p_ext->ee_block),
                                  ext4_ext_get_actual_len(path->p_ext),
                                  ext_pblock(path->p_ext));
                } else
                        ext_debug("  []");
        }
        ext_debug("\n");
}

static void ext4_ext_show_leaf(struct inode *inode, struct ext4_ext_path *path)
{
        int depth = ext_depth(inode);
        struct ext4_extent_header *eh;
        struct ext4_extent *ex;
        int i;

        if (!path)
                return;

        eh = path[depth].p_hdr;
        ex = EXT_FIRST_EXTENT(eh);

        for (i = 0; i < le16_to_cpu(eh->eh_entries); i++, ex++) {
                ext_debug("%d:%d:%llu ", le32_to_cpu(ex->ee_block),
                          ext4_ext_get_actual_len(ex), ext_pblock(ex));
        }
        ext_debug("\n");
}
#else
#define ext4_ext_show_path(inode,path)
#define ext4_ext_show_leaf(inode,path)
#endif

static void ext4_ext_drop_refs(struct ext4_ext_path *path)
{
        int depth = path->p_depth;
        int i;

        for (i = 0; i <= depth; i++, path++)
                if (path->p_bh) {
                        brelse(path->p_bh);
                        path->p_bh = NULL;
                }
}

/*
 * ext4_ext_binsearch_idx:
 * binary search for the closest index of the given block
 * the header must be checked before calling this
 */
static void
ext4_ext_binsearch_idx(struct inode *inode,
                        struct ext4_ext_path *path, ext4_lblk_t block)
{
        struct ext4_extent_header *eh = path->p_hdr;
        struct ext4_extent_idx *r, *l, *m;


        ext_debug("binsearch for %u(idx):  ", block);

        l = EXT_FIRST_INDEX(eh) + 1;
        r = EXT_LAST_INDEX(eh);
        while (l <= r) {
                m = l + (r - l) / 2;
                if (block < le32_to_cpu(m->ei_block))
                        r = m - 1;
                else
                        l = m + 1;
                ext_debug("%p(%u):%p(%u):%p(%u) ", l, le32_to_cpu(l->ei_block),
                                m, le32_to_cpu(m->ei_block),
                                r, le32_to_cpu(r->ei_block));
        }

        path->p_idx = l - 1;
        ext_debug("  -> %d->%lld ", le32_to_cpu(path->p_idx->ei_block),
                  idx_pblock(path->p_idx));

#ifdef CHECK_BINSEARCH
        {
                struct ext4_extent_idx *chix, *ix;
                int k;

                chix = ix = EXT_FIRST_INDEX(eh);
                for (k = 0; k < le16_to_cpu(eh->eh_entries); k++, ix++) {
                  if (k != 0 &&
                      le32_to_cpu(ix->ei_block) <= le32_to_cpu(ix[-1].ei_block)) {
                                printk("k=%d, ix=0x%p, first=0x%p\n", k,
                                        ix, EXT_FIRST_INDEX(eh));
                                printk("%u <= %u\n",
                                       le32_to_cpu(ix->ei_block),
                                       le32_to_cpu(ix[-1].ei_block));
                        }
                        BUG_ON(k && le32_to_cpu(ix->ei_block)
                                           <= le32_to_cpu(ix[-1].ei_block));
                        if (block < le32_to_cpu(ix->ei_block))
                                break;
                        chix = ix;
                }
                BUG_ON(chix != path->p_idx);
        }
#endif

}

/*
 * ext4_ext_binsearch:
 * binary search for closest extent of the given block
 * the header must be checked before calling this
 */
static void
ext4_ext_binsearch(struct inode *inode,
                struct ext4_ext_path *path, ext4_lblk_t block)
{
        struct ext4_extent_header *eh = path->p_hdr;
        struct ext4_extent *r, *l, *m;

        if (eh->eh_entries == 0) {
                /*
                 * this leaf is empty:
                 * we get such a leaf in split/add case
                 */
                return;
        }

        ext_debug("binsearch for %u:  ", block);

        l = EXT_FIRST_EXTENT(eh) + 1;
        r = EXT_LAST_EXTENT(eh);

        while (l <= r) {
                m = l + (r - l) / 2;
                if (block < le32_to_cpu(m->ee_block))
                        r = m - 1;
                else
                        l = m + 1;
                ext_debug("%p(%u):%p(%u):%p(%u) ", l, le32_to_cpu(l->ee_block),
                                m, le32_to_cpu(m->ee_block),
                                r, le32_to_cpu(r->ee_block));
        }

        path->p_ext = l - 1;
        ext_debug("  -> %d:%llu:%d ",
                        le32_to_cpu(path->p_ext->ee_block),
                        ext_pblock(path->p_ext),
                        ext4_ext_get_actual_len(path->p_ext));

#ifdef CHECK_BINSEARCH
        {
                struct ext4_extent *chex, *ex;
                int k;

                chex = ex = EXT_FIRST_EXTENT(eh);
                for (k = 0; k < le16_to_cpu(eh->eh_entries); k++, ex++) {
                        BUG_ON(k && le32_to_cpu(ex->ee_block)
                                          <= le32_to_cpu(ex[-1].ee_block));
                        if (block < le32_to_cpu(ex->ee_block))
                                break;
                        chex = ex;
                }
                BUG_ON(chex != path->p_ext);
        }
#endif

}

int ext4_ext_tree_init(handle_t *handle, struct inode *inode)
{
        struct ext4_extent_header *eh;

        eh = ext_inode_hdr(inode);
        eh->eh_depth = 0;
        eh->eh_entries = 0;
        eh->eh_magic = EXT4_EXT_MAGIC;
        eh->eh_max = cpu_to_le16(ext4_ext_space_root(inode));
        ext4_mark_inode_dirty(handle, inode);
        ext4_ext_invalidate_cache(inode);
        return 0;
}

struct ext4_ext_path *
ext4_ext_find_extent(struct inode *inode, ext4_lblk_t block,
                                        struct ext4_ext_path *path)
{
        struct ext4_extent_header *eh;
        struct buffer_head *bh;
        short int depth, i, ppos = 0, alloc = 0;

        eh = ext_inode_hdr(inode);
        depth = ext_depth(inode);
        if (ext4_ext_check_header(inode, eh, depth))
                return ERR_PTR(-EIO);


        /* account possible depth increase */
        if (!path) {
                path = kzalloc(sizeof(struct ext4_ext_path) * (depth + 2),
                                GFP_NOFS);
                if (!path)
                        return ERR_PTR(-ENOMEM);
                alloc = 1;
        }
        path[0].p_hdr = eh;

        i = depth;
        /* walk through the tree */
        while (i) {
                ext_debug("depth %d: num %d, max %d\n",
                          ppos, le16_to_cpu(eh->eh_entries), le16_to_cpu(eh->eh_max));

                ext4_ext_binsearch_idx(inode, path + ppos, block);
                path[ppos].p_block = idx_pblock(path[ppos].p_idx);
                path[ppos].p_depth = i;
                path[ppos].p_ext = NULL;

                bh = sb_bread(inode->i_sb, path[ppos].p_block);
                if (!bh)
                        goto err;

                eh = ext_block_hdr(bh);
                ppos++;
                BUG_ON(ppos > depth);
                path[ppos].p_bh = bh;
                path[ppos].p_hdr = eh;
                i--;

                if (ext4_ext_check_header(inode, eh, i))
                        goto err;
        }

        path[ppos].p_depth = i;
        path[ppos].p_hdr = eh;
        path[ppos].p_ext = NULL;
        path[ppos].p_idx = NULL;

        /* find extent */
        ext4_ext_binsearch(inode, path + ppos, block);

        ext4_ext_show_path(inode, path);

        return path;

err:
        ext4_ext_drop_refs(path);
        if (alloc)
                kfree(path);
        return ERR_PTR(-EIO);
}

/*
 * ext4_ext_insert_index:
 * insert new index [@logical;@ptr] into the block at @curp;
 * check where to insert: before @curp or after @curp
 */
static int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
                                struct ext4_ext_path *curp,
                                int logical, ext4_fsblk_t ptr)
{
        struct ext4_extent_idx *ix;
        int len, err;

        err = ext4_ext_get_access(handle, inode, curp);
        if (err)
                return err;

        BUG_ON(logical == le32_to_cpu(curp->p_idx->ei_block));
        len = EXT_MAX_INDEX(curp->p_hdr) - curp->p_idx;
        if (logical > le32_to_cpu(curp->p_idx->ei_block)) {
                /* insert after */
                if (curp->p_idx != EXT_LAST_INDEX(curp->p_hdr)) {
                        len = (len - 1) * sizeof(struct ext4_extent_idx);
                        len = len < 0 ? 0 : len;
                        ext_debug("insert new index %d after: %llu. "
                                        "move %d from 0x%p to 0x%p\n",
                                        logical, ptr, len,
                                        (curp->p_idx + 1), (curp->p_idx + 2));
                        memmove(curp->p_idx + 2, curp->p_idx + 1, len);
                }
                ix = curp->p_idx + 1;
        } else {
                /* insert before */
                len = len * sizeof(struct ext4_extent_idx);
                len = len < 0 ? 0 : len;
                ext_debug("insert new index %d before: %llu. "
                                "move %d from 0x%p to 0x%p\n",
                                logical, ptr, len,
                                curp->p_idx, (curp->p_idx + 1));
                memmove(curp->p_idx + 1, curp->p_idx, len);
                ix = curp->p_idx;
        }

        ix->ei_block = cpu_to_le32(logical);
        ext4_idx_store_pblock(ix, ptr);
        curp->p_hdr->eh_entries = cpu_to_le16(le16_to_cpu(curp->p_hdr->eh_entries)+1);

        BUG_ON(le16_to_cpu(curp->p_hdr->eh_entries)
                             > le16_to_cpu(curp->p_hdr->eh_max));
        BUG_ON(ix > EXT_LAST_INDEX(curp->p_hdr));

        err = ext4_ext_dirty(handle, inode, curp);
        ext4_std_error(inode->i_sb, err);

        return err;
}

/*
 * ext4_ext_split:
 * inserts new subtree into the path, using free index entry
 * at depth @at:
 * - allocates all needed blocks (new leaf and all intermediate index blocks)
 * - makes decision where to split
 * - moves remaining extents and index entries (right to the split point)
 *   into the newly allocated blocks
 * - initializes subtree
 */
static int ext4_ext_split(handle_t *handle, struct inode *inode,
                                struct ext4_ext_path *path,
                                struct ext4_extent *newext, int at)
{
        struct buffer_head *bh = NULL;
        int depth = ext_depth(inode);
        struct ext4_extent_header *neh;
        struct ext4_extent_idx *fidx;
        struct ext4_extent *ex;
        int i = at, k, m, a;
        ext4_fsblk_t newblock, oldblock;
        __le32 border;
        ext4_fsblk_t *ablocks = NULL; /* array of allocated blocks */
        int err = 0;

        /* make decision: where to split? */
        /* FIXME: now decision is simplest: at current extent */

        /* if current leaf will be split, then we should use
         * border from split point */
        BUG_ON(path[depth].p_ext > EXT_MAX_EXTENT(path[depth].p_hdr));
        if (path[depth].p_ext != EXT_MAX_EXTENT(path[depth].p_hdr)) {
                border = path[depth].p_ext[1].ee_block;
                ext_debug("leaf will be split."
                                " next leaf starts at %d\n",
                                  le32_to_cpu(border));
        } else {
                border = newext->ee_block;
                ext_debug("leaf will be added."
                                " next leaf starts at %d\n",
                                le32_to_cpu(border));
        }

        /*
         * If error occurs, then we break processing
         * and mark filesystem read-only. index won't
         * be inserted and tree will be in consistent
         * state. Next mount will repair buffers too.
         */

        /*
         * Get array to track all allocated blocks.
         * We need this to handle errors and free blocks
         * upon them.
         */
        ablocks = kzalloc(sizeof(ext4_fsblk_t) * depth, GFP_NOFS);
        if (!ablocks)
                return -ENOMEM;

        /* allocate all needed blocks */
        ext_debug("allocate %d blocks for indexes/leaf\n", depth - at);
        for (a = 0; a < depth - at; a++) {
                newblock = ext4_ext_new_block(handle, inode, path, newext, &err);
                if (newblock == 0)
                        goto cleanup;
                ablocks[a] = newblock;
        }

        /* initialize new leaf */
        newblock = ablocks[--a];
        BUG_ON(newblock == 0);
        bh = sb_getblk(inode->i_sb, newblock);
        if (!bh) {
                err = -EIO;
                goto cleanup;
        }
        lock_buffer(bh);

        err = ext4_journal_get_create_access(handle, bh);
        if (err)
                goto cleanup;

        neh = ext_block_hdr(bh);
        neh->eh_entries = 0;
        neh->eh_max = cpu_to_le16(ext4_ext_space_block(inode));
        neh->eh_magic = EXT4_EXT_MAGIC;
        neh->eh_depth = 0;
        ex = EXT_FIRST_EXTENT(neh);

        /* move remainder of path[depth] to the new leaf */
        BUG_ON(path[depth].p_hdr->eh_entries != path[depth].p_hdr->eh_max);
        /* start copy from next extent */
        /* TODO: we could do it by single memmove */
        m = 0;
        path[depth].p_ext++;
        while (path[depth].p_ext <=
                        EXT_MAX_EXTENT(path[depth].p_hdr)) {
                ext_debug("move %d:%llu:%d in new leaf %llu\n",
                                le32_to_cpu(path[depth].p_ext->ee_block),
                                ext_pblock(path[depth].p_ext),
                                ext4_ext_get_actual_len(path[depth].p_ext),
                                newblock);
                /*memmove(ex++, path[depth].p_ext++,
                                sizeof(struct ext4_extent));
                neh->eh_entries++;*/
                path[depth].p_ext++;
                m++;
        }
        if (m) {
                memmove(ex, path[depth].p_ext-m, sizeof(struct ext4_extent)*m);
                neh->eh_entries = cpu_to_le16(le16_to_cpu(neh->eh_entries)+m);
        }

        set_buffer_uptodate(bh);
        unlock_buffer(bh);

        err = ext4_journal_dirty_metadata(handle, bh);
        if (err)
                goto cleanup;
        brelse(bh);
        bh = NULL;

        /* correct old leaf */
        if (m) {
                err = ext4_ext_get_access(handle, inode, path + depth);
                if (err)
                        goto cleanup;
                path[depth].p_hdr->eh_entries =
                     cpu_to_le16(le16_to_cpu(path[depth].p_hdr->eh_entries)-m);
                err = ext4_ext_dirty(handle, inode, path + depth);
                if (err)
                        goto cleanup;

        }

        /* create intermediate indexes */
        k = depth - at - 1;
        BUG_ON(k < 0);
        if (k)
                ext_debug("create %d intermediate indices\n", k);
        /* insert new index into current index block */
        /* current depth stored in i var */
        i = depth - 1;
        while (k--) {
                oldblock = newblock;
                newblock = ablocks[--a];
                bh = sb_getblk(inode->i_sb, newblock);
                if (!bh) {
                        err = -EIO;
                        goto cleanup;
                }
                lock_buffer(bh);

                err = ext4_journal_get_create_access(handle, bh);
                if (err)
                        goto cleanup;

                neh = ext_block_hdr(bh);
                neh->eh_entries = cpu_to_le16(1);
                neh->eh_magic = EXT4_EXT_MAGIC;
                neh->eh_max = cpu_to_le16(ext4_ext_space_block_idx(inode));
                neh->eh_depth = cpu_to_le16(depth - i);
                fidx = EXT_FIRST_INDEX(neh);
                fidx->ei_block = border;
                ext4_idx_store_pblock(fidx, oldblock);

                ext_debug("int.index at %d (block %llu): %u -> %llu\n",
                                i, newblock, le32_to_cpu(border), oldblock);
                /* copy indexes */
                m = 0;
                path[i].p_idx++;

                ext_debug("cur 0x%p, last 0x%p\n", path[i].p_idx,
                                EXT_MAX_INDEX(path[i].p_hdr));
                BUG_ON(EXT_MAX_INDEX(path[i].p_hdr) !=
                                EXT_LAST_INDEX(path[i].p_hdr));
                while (path[i].p_idx <= EXT_MAX_INDEX(path[i].p_hdr)) {
                        ext_debug("%d: move %d:%llu in new index %llu\n", i,
                                        le32_to_cpu(path[i].p_idx->ei_block),
                                        idx_pblock(path[i].p_idx),
                                        newblock);
                        /*memmove(++fidx, path[i].p_idx++,
                                        sizeof(struct ext4_extent_idx));
                        neh->eh_entries++;
                        BUG_ON(neh->eh_entries > neh->eh_max);*/
                        path[i].p_idx++;
                        m++;
                }
                if (m) {
                        memmove(++fidx, path[i].p_idx - m,
                                sizeof(struct ext4_extent_idx) * m);
                        neh->eh_entries =
                                cpu_to_le16(le16_to_cpu(neh->eh_entries) + m);
                }
                set_buffer_uptodate(bh);
                unlock_buffer(bh);

                err = ext4_journal_dirty_metadata(handle, bh);
                if (err)
                        goto cleanup;
                brelse(bh);
                bh = NULL;

                /* correct old index */
                if (m) {
                        err = ext4_ext_get_access(handle, inode, path + i);
                        if (err)
                                goto cleanup;
                        path[i].p_hdr->eh_entries = cpu_to_le16(le16_to_cpu(path[i].p_hdr->eh_entries)-m);
                        err = ext4_ext_dirty(handle, inode, path + i);
                        if (err)
                                goto cleanup;
                }

                i--;
        }

        /* insert new index */
        err = ext4_ext_insert_index(handle, inode, path + at,
                                    le32_to_cpu(border), newblock);

cleanup:
        if (bh) {
                if (buffer_locked(bh))
                        unlock_buffer(bh);
                brelse(bh);
        }

        if (err) {
                /* free all allocated blocks in error case */
                for (i = 0; i < depth; i++) {
                        if (!ablocks[i])
                                continue;
                        ext4_free_blocks(handle, inode, ablocks[i], 1);
                }
        }
        kfree(ablocks);

        return err;
}

/*
 * ext4_ext_grow_indepth:
 * implements tree growing procedure:
 * - allocates new block
 * - moves top-level data (index block or leaf) into the new block
 * - initializes new top-level, creating index that points to the
 *   just created block
 */
static int ext4_ext_grow_indepth(handle_t *handle, struct inode *inode,
                                        struct ext4_ext_path *path,
                                        struct ext4_extent *newext)
{
        struct ext4_ext_path *curp = path;
        struct ext4_extent_header *neh;
        struct ext4_extent_idx *fidx;
        struct buffer_head *bh;
        ext4_fsblk_t newblock;
        int err = 0;

        newblock = ext4_ext_new_block(handle, inode, path, newext, &err);
        if (newblock == 0)
                return err;

        bh = sb_getblk(inode->i_sb, newblock);
        if (!bh) {
                err = -EIO;
                ext4_std_error(inode->i_sb, err);
                return err;
        }
        lock_buffer(bh);

        err = ext4_journal_get_create_access(handle, bh);
        if (err) {
                unlock_buffer(bh);
                goto out;
        }

        /* move top-level index/leaf into new block */
        memmove(bh->b_data, curp->p_hdr, sizeof(EXT4_I(inode)->i_data));

        /* set size of new block */
        neh = ext_block_hdr(bh);
        /* old root could have indexes or leaves
         * so calculate e_max right way */
        if (ext_depth(inode))
          neh->eh_max = cpu_to_le16(ext4_ext_space_block_idx(inode));
        else
          neh->eh_max = cpu_to_le16(ext4_ext_space_block(inode));
        neh->eh_magic = EXT4_EXT_MAGIC;
        set_buffer_uptodate(bh);
        unlock_buffer(bh);

        err = ext4_journal_dirty_metadata(handle, bh);
        if (err)
                goto out;

        /* create index in new top-level index: num,max,pointer */
        err = ext4_ext_get_access(handle, inode, curp);
        if (err)
                goto out;

        curp->p_hdr->eh_magic = EXT4_EXT_MAGIC;
        curp->p_hdr->eh_max = cpu_to_le16(ext4_ext_space_root_idx(inode));
        curp->p_hdr->eh_entries = cpu_to_le16(1);
        curp->p_idx = EXT_FIRST_INDEX(curp->p_hdr);

        if (path[0].p_hdr->eh_depth)
                curp->p_idx->ei_block =
                        EXT_FIRST_INDEX(path[0].p_hdr)->ei_block;
        else
                curp->p_idx->ei_block =
                        EXT_FIRST_EXTENT(path[0].p_hdr)->ee_block;
        ext4_idx_store_pblock(curp->p_idx, newblock);

        neh = ext_inode_hdr(inode);
        fidx = EXT_FIRST_INDEX(neh);
        ext_debug("new root: num %d(%d), lblock %d, ptr %llu\n",
                  le16_to_cpu(neh->eh_entries), le16_to_cpu(neh->eh_max),
                  le32_to_cpu(fidx->ei_block), idx_pblock(fidx));

        neh->eh_depth = cpu_to_le16(path->p_depth + 1);
        err = ext4_ext_dirty(handle, inode, curp);
out:
        brelse(bh);

        return err;
}

/*
 * ext4_ext_create_new_leaf:
 * finds empty index and adds new leaf.
 * if no free index is found, then it requests in-depth growing.
 */
static int ext4_ext_create_new_leaf(handle_t *handle, struct inode *inode,
                                        struct ext4_ext_path *path,
                                        struct ext4_extent *newext)
{
        struct ext4_ext_path *curp;
        int depth, i, err = 0;

repeat:
        i = depth = ext_depth(inode);

        /* walk up to the tree and look for free index entry */
        curp = path + depth;
        while (i > 0 && !EXT_HAS_FREE_INDEX(curp)) {
                i--;
                curp--;
        }

        /* we use already allocated block for index block,
         * so subsequent data blocks should be contiguous */
        if (EXT_HAS_FREE_INDEX(curp)) {
                /* if we found index with free entry, then use that
                 * entry: create all needed subtree and add new leaf */
                err = ext4_ext_split(handle, inode, path, newext, i);

                /* refill path */
                ext4_ext_drop_refs(path);
                path = ext4_ext_find_extent(inode,
                                    (ext4_lblk_t)le32_to_cpu(newext->ee_block),
                                    path);
                if (IS_ERR(path))
                        err = PTR_ERR(path);
        } else {
                /* tree is full, time to grow in depth */
                err = ext4_ext_grow_indepth(handle, inode, path, newext);
                if (err)
                        goto out;

                /* refill path */
                ext4_ext_drop_refs(path);
                path = ext4_ext_find_extent(inode,
                                   (ext4_lblk_t)le32_to_cpu(newext->ee_block),
                                    path);
                if (IS_ERR(path)) {
                        err = PTR_ERR(path);
                        goto out;
                }

                /*
                 * only first (depth 0 -> 1) produces free space;
                 * in all other cases we have to split the grown tree
                 */
                depth = ext_depth(inode);
                if (path[depth].p_hdr->eh_entries == path[depth].p_hdr->eh_max) {
                        /* now we need to split */
                        goto repeat;
                }
        }

out:
        return err;
}

/*
 * ext4_ext_next_allocated_block:
 * returns allocated block in subsequent extent or EXT_MAX_BLOCK.
 * NOTE: it considers block number from index entry as
 * allocated block. Thus, index entries have to be consistent
 * with leaves.
 */
static ext4_lblk_t
ext4_ext_next_allocated_block(struct ext4_ext_path *path)
{
        int depth;

        BUG_ON(path == NULL);
        depth = path->p_depth;

        if (depth == 0 && path->p_ext == NULL)
                return EXT_MAX_BLOCK;

        while (depth >= 0) {
                if (depth == path->p_depth) {
                        /* leaf */
                        if (path[depth].p_ext !=
                                        EXT_LAST_EXTENT(path[depth].p_hdr))
                          return le32_to_cpu(path[depth].p_ext[1].ee_block);
                } else {
                        /* index */
                        if (path[depth].p_idx !=
                                        EXT_LAST_INDEX(path[depth].p_hdr))
                          return le32_to_cpu(path[depth].p_idx[1].ei_block);
                }
                depth--;
        }

        return EXT_MAX_BLOCK;
}

/*
 * ext4_ext_next_leaf_block:
 * returns first allocated block from next leaf or EXT_MAX_BLOCK
 */
static ext4_lblk_t ext4_ext_next_leaf_block(struct inode *inode,
                                        struct ext4_ext_path *path)
{
        int depth;

        BUG_ON(path == NULL);
        depth = path->p_depth;

        /* zero-tree has no leaf blocks at all */
        if (depth == 0)
                return EXT_MAX_BLOCK;

        /* go to index block */
        depth--;

        while (depth >= 0) {
                if (path[depth].p_idx !=
                                EXT_LAST_INDEX(path[depth].p_hdr))
                        return (ext4_lblk_t)
                                le32_to_cpu(path[depth].p_idx[1].ei_block);
                depth--;
        }

        return EXT_MAX_BLOCK;
}

/*
 * ext4_ext_correct_indexes:
 * if leaf gets modified and modified extent is first in the leaf,
 * then we have to correct all indexes above.
 * TODO: do we need to correct tree in all cases?
 */
static int ext4_ext_correct_indexes(handle_t *handle, struct inode *inode,
                                struct ext4_ext_path *path)
{
        struct ext4_extent_header *eh;
        int depth = ext_depth(inode);
        struct ext4_extent *ex;
        __le32 border;
        int k, err = 0;

        eh = path[depth].p_hdr;
        ex = path[depth].p_ext;
        BUG_ON(ex == NULL);
        BUG_ON(eh == NULL);

        if (depth == 0) {
                /* there is no tree at all */
                return 0;
        }

        if (ex != EXT_FIRST_EXTENT(eh)) {
                /* we correct tree if first leaf got modified only */
                return 0;
        }

        /*
         * TODO: we need correction if border is smaller than current one
         */
        k = depth - 1;
        border = path[depth].p_ext->ee_block;
        err = ext4_ext_get_access(handle, inode, path + k);
        if (err)
                return err;
        path[k].p_idx->ei_block = border;
        err = ext4_ext_dirty(handle, inode, path + k);
        if (err)
                return err;

        while (k--) {
                /* change all left-side indexes */
                if (path[k+1].p_idx != EXT_FIRST_INDEX(path[k+1].p_hdr))
                        break;
                err = ext4_ext_get_access(handle, inode, path + k);
                if (err)
                        break;
                path[k].p_idx->ei_block = border;
                err = ext4_ext_dirty(handle, inode, path + k);
                if (err)
                        break;
        }

        return err;
}

static int
ext4_can_extents_be_merged(struct inode *inode, struct ext4_extent *ex1,
                                struct ext4_extent *ex2)
{
        unsigned short ext1_ee_len, ext2_ee_len, max_len;

        /*
         * Make sure that either both extents are uninitialized, or
         * both are _not_.
         */
        if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2))
                return 0;

        if (ext4_ext_is_uninitialized(ex1))
                max_len = EXT_UNINIT_MAX_LEN;
        else
                max_len = EXT_INIT_MAX_LEN;

        ext1_ee_len = ext4_ext_get_actual_len(ex1);
        ext2_ee_len = ext4_ext_get_actual_len(ex2);

        if (le32_to_cpu(ex1->ee_block) + ext1_ee_len !=
                        le32_to_cpu(ex2->ee_block))
                return 0;

        /*
         * To allow future support for preallocated extents to be added
         * as an RO_COMPAT feature, refuse to merge to extents if
         * this can result in the top bit of ee_len being set.
         */
        if (ext1_ee_len + ext2_ee_len > max_len)
                return 0;
#ifdef AGGRESSIVE_TEST
        if (le16_to_cpu(ex1->ee_len) >= 4)
                return 0;
#endif

        if (ext_pblock(ex1) + ext1_ee_len == ext_pblock(ex2))
                return 1;
        return 0;
}

/*
 * This function tries to merge the "ex" extent to the next extent in the tree.
 * It always tries to merge towards right. If you want to merge towards
 * left, pass "ex - 1" as argument instead of "ex".
 * Returns 0 if the extents (ex and ex+1) were _not_ merged and returns
 * 1 if they got merged.
 */
int ext4_ext_try_to_merge(struct inode *inode,
                          struct ext4_ext_path *path,
                          struct ext4_extent *ex)
{
        struct ext4_extent_header *eh;
        unsigned int depth, len;
        int merge_done = 0;
        int uninitialized = 0;

        depth = ext_depth(inode);
        BUG_ON(path[depth].p_hdr == NULL);
        eh = path[depth].p_hdr;

        while (ex < EXT_LAST_EXTENT(eh)) {
                if (!ext4_can_extents_be_merged(inode, ex, ex + 1))
                        break;
                /* merge with next extent! */
                if (ext4_ext_is_uninitialized(ex))
                        uninitialized = 1;
                ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)
                                + ext4_ext_get_actual_len(ex + 1));
                if (uninitialized)
                        ext4_ext_mark_uninitialized(ex);

                if (ex + 1 < EXT_LAST_EXTENT(eh)) {
                        len = (EXT_LAST_EXTENT(eh) - ex - 1)
                                * sizeof(struct ext4_extent);
                        memmove(ex + 1, ex + 2, len);
                }
                eh->eh_entries = cpu_to_le16(le16_to_cpu(eh->eh_entries) - 1);
                merge_done = 1;
                WARN_ON(eh->eh_entries == 0);
                if (!eh->eh_entries)
                        ext4_error(inode->i_sb, "ext4_ext_try_to_merge",
                           "inode#%lu, eh->eh_entries = 0!", inode->i_ino);
        }

        return merge_done;
}

/*
 * check if a portion of the "newext" extent overlaps with an
 * existing extent.
 *
 * If there is an overlap discovered, it updates the length of the newext
 * such that there will be no overlap, and then returns 1.
 * If there is no overlap found, it returns 0.
 */
unsigned int ext4_ext_check_overlap(struct inode *inode,
                                    struct ext4_extent *newext,
                                    struct ext4_ext_path *path)
{
        ext4_lblk_t b1, b2;
        unsigned int depth, len1;
        unsigned int ret = 0;

        b1 = le32_to_cpu(newext->ee_block);
        len1 = ext4_ext_get_actual_len(newext);
        depth = ext_depth(inode);
        if (!path[depth].p_ext)
                goto out;
        b2 = le32_to_cpu(path[depth].p_ext->ee_block);

        /*
         * get the next allocated block if the extent in the path
         * is before the requested block(s) 
         */
        if (b2 < b1) {
                b2 = ext4_ext_next_allocated_block(path);
                if (b2 == EXT_MAX_BLOCK)
                        goto out;
        }

        /* check for wrap through zero on extent logical start block*/
        if (b1 + len1 < b1) {
                len1 = EXT_MAX_BLOCK - b1;
                newext->ee_len = cpu_to_le16(len1);
                ret = 1;
        }

        /* check for overlap */
        if (b1 + len1 > b2) {
                newext->ee_len = cpu_to_le16(b2 - b1);
                ret = 1;
        }
out:
        return ret;
}

/*
 * ext4_ext_insert_extent:
 * tries to merge requsted extent into the existing extent or
 * inserts requested extent as new one into the tree,
 * creating new leaf in the no-space case.
 */
int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
                                struct ext4_ext_path *path,
                                struct ext4_extent *newext)
{
        struct ext4_extent_header * eh;
        struct ext4_extent *ex, *fex;
        struct ext4_extent *nearex; /* nearest extent */
        struct ext4_ext_path *npath = NULL;
        int depth, len, err;
        ext4_lblk_t next;
        unsigned uninitialized = 0;

        BUG_ON(ext4_ext_get_actual_len(newext) == 0);
        depth = ext_depth(inode);
        ex = path[depth].p_ext;
        BUG_ON(path[depth].p_hdr == NULL);

        /* try to insert block into found extent and return */
        if (ex && ext4_can_extents_be_merged(inode, ex, newext)) {
                ext_debug("append %d block to %d:%d (from %llu)\n",
                                ext4_ext_get_actual_len(newext),
                                le32_to_cpu(ex->ee_block),
                                ext4_ext_get_actual_len(ex), ext_pblock(ex));
                err = ext4_ext_get_access(handle, inode, path + depth);
                if (err)
                        return err;

                /*
                 * ext4_can_extents_be_merged should have checked that either
                 * both extents are uninitialized, or both aren't. Thus we
                 * need to check only one of them here.
                 */
                if (ext4_ext_is_uninitialized(ex))
                        uninitialized = 1;
                ex->ee_len = cpu_to_le16(ext4_ext_get_actual_len(ex)
                                        + ext4_ext_get_actual_len(newext));
                if (uninitialized)
                        ext4_ext_mark_uninitialized(ex);
                eh = path[depth].p_hdr;
                nearex = ex;
                goto merge;
        }

repeat:
        depth = ext_depth(inode);
        eh = path[depth].p_hdr;
        if (le16_to_cpu(eh->eh_entries) < le16_to_cpu(eh->eh_max))
                goto has_space;

        /* probably next leaf has space for us? */
        fex = EXT_LAST_EXTENT(eh);
        next = ext4_ext_next_leaf_block(inode, path);
        if (le32_to_cpu(newext->ee_block) > le32_to_cpu(fex->ee_block)
            && next != EXT_MAX_BLOCK) {
                ext_debug("next leaf block - %d\n", next);
                BUG_ON(npath != NULL);
                npath = ext4_ext_find_extent(inode, next, NULL);
                if (IS_ERR(npath))
                        return PTR_ERR(npath);
                BUG_ON(npath->p_depth != path->p_depth);
                eh = npath[depth].p_hdr;
                if (le16_to_cpu(eh->eh_entries) < le16_to_cpu(eh->eh_max)) {
                        ext_debug("next leaf isnt full(%d)\n",
                                  le16_to_cpu(eh->eh_entries));
                        path = npath;
                        goto repeat;
                }
                ext_debug("next leaf has no free space(%d,%d)\n",
                          le16_to_cpu(eh->eh_entries), le16_to_cpu(eh->eh_max));
        }

        /*
         * There is no free space in the found leaf.
         * We're gonna add a new leaf in the tree.
         */
        err = ext4_ext_create_new_leaf(handle, inode, path, newext);
        if (err)
                goto cleanup;
        depth = ext_depth(inode);
        eh = path[depth].p_hdr;

has_space:
        nearex = path[depth].p_ext;

        err = ext4_ext_get_access(handle, inode, path + depth);
        if (err)
                goto cleanup;

        if (!nearex) {
                /* there is no extent in this leaf, create first one */
                ext_debug("first extent in the leaf: %d:%llu:%d\n",
                                le32_to_cpu(newext->ee_block),
                                ext_pblock(newext),
                                ext4_ext_get_actual_len(newext));
                path[depth].p_ext = EXT_FIRST_EXTENT(eh);
        } else if (le32_to_cpu(newext->ee_block)
                           > le32_to_cpu(nearex->ee_block)) {
/*              BUG_ON(newext->ee_block == nearex->ee_block); */
                if (nearex != EXT_LAST_EXTENT(eh)) {
                        len = EXT_MAX_EXTENT(eh) - nearex;
                        len = (len - 1) * sizeof(struct ext4_extent);
                        len = len < 0 ? 0 : len;
                        ext_debug("insert %d:%llu:%d after: nearest 0x%p, "
                                        "move %d from 0x%p to 0x%p\n",
                                        le32_to_cpu(newext->ee_block),
                                        ext_pblock(newext),
                                        ext4_ext_get_actual_len(newext),
                                        nearex, len, nearex + 1, nearex + 2);
                        memmove(nearex + 2, nearex + 1, len);
                }
                path[depth].p_ext = nearex + 1;
        } else {
                BUG_ON(newext->ee_block == nearex->ee_block);
                len = (EXT_MAX_EXTENT(eh) - nearex) * sizeof(struct ext4_extent);
                len = len < 0 ? 0 : len;
                ext_debug("insert %d:%llu:%d before: nearest 0x%p, "
                                "move %d from 0x%p to 0x%p\n",
                                le32_to_cpu(newext->ee_block),
                                ext_pblock(newext),
                                ext4_ext_get_actual_len(newext),
                                nearex, len, nearex + 1, nearex + 2);
                memmove(nearex + 1, nearex, len);
                path[depth].p_ext = nearex;
        }

        eh->eh_entries = cpu_to_le16(le16_to_cpu(eh->eh_entries)+1);
        nearex = path[depth].p_ext;
        nearex->ee_block = newext->ee_block;
        ext4_ext_store_pblock(nearex, ext_pblock(newext));
        nearex->ee_len = newext->ee_len;

merge:
        /* try to merge extents to the right */
        ext4_ext_try_to_merge(inode, path, nearex);

        /* try to merge extents to the left */

        /* time to correct all indexes above */
        err = ext4_ext_correct_indexes(handle, inode, path);
        if (err)
                goto cleanup;

        err = ext4_ext_dirty(handle, inode, path + depth);

cleanup:
        if (npath) {
                ext4_ext_drop_refs(npath);
                kfree(npath);
        }
        ext4_ext_tree_changed(inode);
        ext4_ext_invalidate_cache(inode);
        return err;
}

static void
ext4_ext_put_in_cache(struct inode *inode, ext4_lblk_t block,
                        __u32 len, ext4_fsblk_t start, int type)
{
        struct ext4_ext_cache *cex;
        BUG_ON(len == 0);
        cex = &EXT4_I(inode)->i_cached_extent;
        cex->ec_type = type;
        cex->ec_block = block;
        cex->ec_len = len;
        cex->ec_start = start;
}

/*
 * ext4_ext_put_gap_in_cache:
 * calculate boundaries of the gap that the requested block fits into
 * and cache this gap
 */
static void
ext4_ext_put_gap_in_cache(struct inode *inode, struct ext4_ext_path *path,
                                ext4_lblk_t block)
{
        int depth = ext_depth(inode);
        unsigned long len;
        ext4_lblk_t lblock;
        struct ext4_extent *ex;

        ex = path[depth].p_ext;
        if (ex == NULL) {
                /* there is no extent yet, so gap is [0;-] */
                lblock = 0;
                len = EXT_MAX_BLOCK;
                ext_debug("cache gap(whole file):");
        } else if (block < le32_to_cpu(ex->ee_block)) {
                lblock = block;
                len = le32_to_cpu(ex->ee_block) - block;
                ext_debug("cache gap(before): %u [%u:%u]",
                                block,
                                le32_to_cpu(ex->ee_block),
                                 ext4_ext_get_actual_len(ex));
        } else if (block >= le32_to_cpu(ex->ee_block)
                        + ext4_ext_get_actual_len(ex)) {
                ext4_lblk_t next;
                lblock = le32_to_cpu(ex->ee_block)
                        + ext4_ext_get_actual_len(ex);

                next = ext4_ext_next_allocated_block(path);
                ext_debug("cache gap(after): [%u:%u] %u",
                                le32_to_cpu(ex->ee_block),
                                ext4_ext_get_actual_len(ex),
                                block);
                BUG_ON(next == lblock);
                len = next - lblock;
        } else {
                lblock = len = 0;
                BUG();
        }

        ext_debug(" -> %u:%lu\n", lblock, len);
        ext4_ext_put_in_cache(inode, lblock, len, 0, EXT4_EXT_CACHE_GAP);
}

static int
ext4_ext_in_cache(struct inode *inode, ext4_lblk_t block,
                        struct ext4_extent *ex)
{
        struct ext4_ext_cache *cex;

        cex = &EXT4_I(inode)->i_cached_extent;

        /* has cache valid data? */
        if (cex->ec_type == EXT4_EXT_CACHE_NO)
                return EXT4_EXT_CACHE_NO;

        BUG_ON(cex->ec_type != EXT4_EXT_CACHE_GAP &&
                        cex->ec_type != EXT4_EXT_CACHE_EXTENT);
        if (block >= cex->ec_block && block < cex->ec_block + cex->ec_len) {
                ex->ee_block = cpu_to_le32(cex->ec_block);
                ext4_ext_store_pblock(ex, cex->ec_start);
                ex->ee_len = cpu_to_le16(cex->ec_len);
                ext_debug("%u cached by %u:%u:%llu\n",
                                block,
                                cex->ec_block, cex->ec_len, cex->ec_start);
                return cex->ec_type;
        }

        /* not in cache */
        return EXT4_EXT_CACHE_NO;
}

/*
 * ext4_ext_rm_idx:
 * removes index from the index block.
 * It's used in truncate case only, thus all requests are for
 * last index in the block only.
 */
static int ext4_ext_rm_idx(handle_t *handle, struct inode *inode,
                        struct ext4_ext_path *path)
{
        struct buffer_head *bh;
        int err;
        ext4_fsblk_t leaf;

        /* free index block */
        path--;
        leaf = idx_pblock(path->p_idx);
        BUG_ON(path->p_hdr->eh_entries == 0);
        err = ext4_ext_get_access(handle, inode, path);
        if (err)
                return err;
        path->p_hdr->eh_entries = cpu_to_le16(le16_to_cpu(path->p_hdr->eh_entries)-1);
        err = ext4_ext_dirty(handle, inode, path);
        if (err)
                return err;
        ext_debug("index is empty, remove it, free block %llu\n", leaf);
        bh = sb_find_get_block(inode->i_sb, leaf);
        ext4_forget(handle, 1, inode, bh, leaf);
        ext4_free_blocks(handle, inode, leaf, 1);
        return err;
}

/*
 * ext4_ext_calc_credits_for_insert:
 * This routine returns max. credits that the extent tree can consume.
 * It should be OK for low-performance paths like ->writepage()
 * To allow many writing processes to fit into a single transaction,
 * the caller should calculate credits under truncate_mutex and
 * pass the actual path.
 */
int ext4_ext_calc_credits_for_insert(struct inode *inode,
                                                struct ext4_ext_path *path)
{
        int depth, needed;

        if (path) {
                /* probably there is space in leaf? */
                depth = ext_depth(inode);
                if (le16_to_cpu(path[depth].p_hdr->eh_entries)
                                < le16_to_cpu(path[depth].p_hdr->eh_max))
                        return 1;
        }

        /*
         * given 32-bit logical block (4294967296 blocks), max. tree
         * can be 4 levels in depth -- 4 * 340^4 == 53453440000.
         * Let's also add one more level for imbalance.
         */
        depth = 5;

        /* allocation of new data block(s) */
        needed = 2;

        /*
         * tree can be full, so it would need to grow in depth:
         * we need one credit to modify old root, credits for
         * new root will be added in split accounting
         */
        needed += 1;

        /*
         * Index split can happen, we would need:
         *    allocate intermediate indexes (bitmap + group)
         *  + change two blocks at each level, but root (already included)
         */
        needed += (depth * 2) + (depth * 2);

        /* any allocation modifies superblock */
        needed += 1;

        return needed;
}

static int ext4_remove_blocks(handle_t *handle, struct inode *inode,
                                struct ext4_extent *ex,
                                ext4_lblk_t from, ext4_lblk_t to)
{
        struct buffer_head *bh;
        unsigned short ee_len =  ext4_ext_get_actual_len(ex);
        int i;

#ifdef EXTENTS_STATS
        {
                struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
                spin_lock(&sbi->s_ext_stats_lock);
                sbi->s_ext_blocks += ee_len;
                sbi->s_ext_extents++;
                if (ee_len < sbi->s_ext_min)
                        sbi->s_ext_min = ee_len;
                if (ee_len > sbi->s_ext_max)
                        sbi->s_ext_max = ee_len;
                if (ext_depth(inode) > sbi->s_depth_max)
                        sbi->s_depth_max = ext_depth(inode);
                spin_unlock(&sbi->s_ext_stats_lock);
        }
#endif
        if (from >= le32_to_cpu(ex->ee_block)
            && to == le32_to_cpu(ex->ee_block) + ee_len - 1) {
                /* tail removal */
                ext4_lblk_t num;
                ext4_fsblk_t start;

                num = le32_to_cpu(ex->ee_block) + ee_len - from;
                start = ext_pblock(ex) + ee_len - num;
                ext_debug("free last %u blocks starting %llu\n", num, start);
                for (i = 0; i < num; i++) {
                        bh = sb_find_get_block(inode->i_sb, start + i);
                        ext4_forget(handle, 0, inode, bh, start + i);
                }
                ext4_free_blocks(handle, inode, start, num);
        } else if (from == le32_to_cpu(ex->ee_block)
                   && to <= le32_to_cpu(ex->ee_block) + ee_len - 1) {
                printk(KERN_INFO "strange request: removal %u-%u from %u:%u\n",
                        from, to, le32_to_cpu(ex->ee_block), ee_len);
        } else {
                printk(KERN_INFO "strange request: removal(2) "
                                "%u-%u from %u:%u\n",
                                from, to, le32_to_cpu(ex->ee_block), ee_len);
        }
        return 0;
}

static int
ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
                struct ext4_ext_path *path, ext4_lblk_t start)
{
        int err = 0, correct_index = 0;
        int depth = ext_depth(inode), credits;
        struct ext4_extent_header *eh;
        ext4_lblk_t a, b, block;
        unsigned num;
        ext4_lblk_t ex_ee_block;
        unsigned short ex_ee_len;
        unsigned uninitialized = 0;
        struct ext4_extent *ex;

        /* the header must be checked already in ext4_ext_remove_space() */
        ext_debug("truncate since %u in leaf\n", start);
        if (!path[depth].p_hdr)
                path[depth].p_hdr = ext_block_hdr(path[depth].p_bh);
        eh = path[depth].p_hdr;
        BUG_ON(eh == NULL);

        /* find where to start removing */
        ex = EXT_LAST_EXTENT(eh);

        ex_ee_block = le32_to_cpu(ex->ee_block);
        if (ext4_ext_is_uninitialized(ex))
                uninitialized = 1;
        ex_ee_len = ext4_ext_get_actual_len(ex);

        while (ex >= EXT_FIRST_EXTENT(eh) &&
                        ex_ee_block + ex_ee_len > start) {
                ext_debug("remove ext %lu:%u\n", ex_ee_block, ex_ee_len);
                path[depth].p_ext = ex;

                a = ex_ee_block > start ? ex_ee_block : start;
                b = ex_ee_block + ex_ee_len - 1 < EXT_MAX_BLOCK ?
                        ex_ee_block + ex_ee_len - 1 : EXT_MAX_BLOCK;

                ext_debug("  border %u:%u\n", a, b);

                if (a != ex_ee_block && b != ex_ee_block + ex_ee_len - 1) {
                        block = 0;
                        num = 0;
                        BUG();
                } else if (a != ex_ee_block) {
                        /* remove tail of the extent */
                        block = ex_ee_block;
                        num = a - block;
                } else if (b != ex_ee_block + ex_ee_len - 1) {
                        /* remove head of the extent */
                        block = a;
                        num = b - a;
                        /* there is no "make a hole" API yet */
                        BUG();
                } else {
                        /* remove whole extent: excellent! */
                        block = ex_ee_block;
                        num = 0;
                        BUG_ON(a != ex_ee_block);
                        BUG_ON(b != ex_ee_block + ex_ee_len - 1);
                }

                /* at present, extent can't cross block group: */
                /* leaf + bitmap + group desc + sb + inode */
                credits = 5;
                if (ex == EXT_FIRST_EXTENT(eh)) {
                        correct_index = 1;
                        credits += (ext_depth(inode)) + 1;
                }
#ifdef CONFIG_QUOTA
                credits += 2 * EXT4_QUOTA_TRANS_BLOCKS(inode->i_sb);
#endif

                handle = ext4_ext_journal_restart(handle, credits);
                if (IS_ERR(handle)) {
                        err = PTR_ERR(handle);
                        goto out;
                }

                err = ext4_ext_get_access(handle, inode, path + depth);
                if (err)
                        goto out;

                err = ext4_remove_blocks(handle, inode, ex, a, b);
                if (err)
                        goto out;

                if (num == 0) {
                        /* this extent is removed; mark slot entirely unused */
                        ext4_ext_store_pblock(ex, 0);
                        eh->eh_entries = cpu_to_le16(le16_to_cpu(eh->eh_entries)-1);
                }

                ex->ee_block = cpu_to_le32(block);
                ex->ee_len = cpu_to_le16(num);
                /*
                 * Do not mark uninitialized if all the blocks in the
                 * extent have been removed.
                 */
                if (uninitialized && num)
                        ext4_ext_mark_uninitialized(ex);

                err = ext4_ext_dirty(handle, inode, path + depth);
                if (err)
                        goto out;

                ext_debug("new extent: %u:%u:%llu\n", block, num,
                                ext_pblock(ex));
                ex--;
                ex_ee_block = le32_to_cpu(ex->ee_block);
                ex_ee_len = ext4_ext_get_actual_len(ex);
        }

        if (correct_index && eh->eh_entries)
                err = ext4_ext_correct_indexes(handle, inode, path);

        /* if this leaf is free, then we should
         * remove it from index block above */
        if (err == 0 && eh->eh_entries == 0 && path[depth].p_bh != NULL)
                err = ext4_ext_rm_idx(handle, inode, path + depth);

out:
        return err;
}

/*
 * ext4_ext_more_to_rm:
 * returns 1 if current index has to be freed (even partial)
 */
static int
ext4_ext_more_to_rm(struct ext4_ext_path *path)
{
        BUG_ON(path->p_idx == NULL);

        if (path->p_idx < EXT_FIRST_INDEX(path->p_hdr))
                return 0;

        /*
         * if truncate on deeper level happened, it wasn't partial,
         * so we have to consider current index for truncation
         */
        if (le16_to_cpu(path->p_hdr->eh_entries) == path->p_block)
                return 0;
        return 1;
}

static int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start)
{
        struct super_block *sb = inode->i_sb;
        int depth = ext_depth(inode);
        struct ext4_ext_path *path;
        handle_t *handle;
        int i = 0, err = 0;

        ext_debug("truncate since %u\n", start);

        /* probably first extent we're gonna free will be last in block */
        handle = ext4_journal_start(inode, depth + 1);
        if (IS_ERR(handle))
                return PTR_ERR(handle);

        ext4_ext_invalidate_cache(inode);

        /*
         * We start scanning from right side, freeing all the blocks
         * after i_size and walking into the tree depth-wise.
         */
        path = kzalloc(sizeof(struct ext4_ext_path) * (depth + 1), GFP_KERNEL);
        if (path == NULL) {
                ext4_journal_stop(handle);
                return -ENOMEM;
        }
        path[0].p_hdr = ext_inode_hdr(inode);
        if (ext4_ext_check_header(inode, path[0].p_hdr, depth)) {
                err = -EIO;
                goto out;
        }
        path[0].p_depth = depth;

        while (i >= 0 && err == 0) {
                if (i == depth) {
                        /* this is leaf block */
                        err = ext4_ext_rm_leaf(handle, inode, path, start);
                        /* root level has p_bh == NULL, brelse() eats this */
                        brelse(path[i].p_bh);
                        path[i].p_bh = NULL;
                        i--;
                        continue;
                }

                /* this is index block */
                if (!path[i].p_hdr) {
                        ext_debug("initialize header\n");
                        path[i].p_hdr = ext_block_hdr(path[i].p_bh);
                }

                if (!path[i].p_idx) {
                        /* this level hasn't been touched yet */
                        path[i].p_idx = EXT_LAST_INDEX(path[i].p_hdr);
                        path[i].p_block = le16_to_cpu(path[i].p_hdr->eh_entries)+1;
                        ext_debug("init index ptr: hdr 0x%p, num %d\n",
                                  path[i].p_hdr,
                                  le16_to_cpu(path[i].p_hdr->eh_entries));
                } else {
                        /* we were already here, see at next index */
                        path[i].p_idx--;
                }

                ext_debug("level %d - index, first 0x%p, cur 0x%p\n",
                                i, EXT_FIRST_INDEX(path[i].p_hdr),
                                path[i].p_idx);
                if (ext4_ext_more_to_rm(path + i)) {
                        struct buffer_head *bh;
                        /* go to the next level */
                        ext_debug("move to level %d (block %llu)\n",
                                  i + 1, idx_pblock(path[i].p_idx));
                        memset(path + i + 1, 0, sizeof(*path));
                        bh = sb_bread(sb, idx_pblock(path[i].p_idx));
                        if (!bh) {
                                /* should we reset i_size? */
                                err = -EIO;
                                break;
                        }
                        if (WARN_ON(i + 1 > depth)) {
                                err = -EIO;
                                break;
                        }
                        if (ext4_ext_check_header(inode, ext_block_hdr(bh),
                                                        depth - i - 1)) {
                                err = -EIO;
                                break;
                        }
                        path[i + 1].p_bh = bh;

                        /* save actual number of indexes since this
                         * number is changed at the next iteration */
                        path[i].p_block = le16_to_cpu(path[i].p_hdr->eh_entries);
                        i++;
                } else {
                        /* we finished processing this index, go up */
                        if (path[i].p_hdr->eh_entries == 0 && i > 0) {
                                /* index is empty, remove it;
                                 * handle must be already prepared by the
                                 * truncatei_leaf() */
                                err = ext4_ext_rm_idx(handle, inode, path + i);
                        }
                        /* root level has p_bh == NULL, brelse() eats this */
                        brelse(path[i].p_bh);
                        path[i].p_bh = NULL;
                        i--;
                        ext_debug("return to level %d\n", i);
                }
        }

        /* TODO: flexible tree reduction should be here */
        if (path->p_hdr->eh_entries == 0) {
                /*
                 * truncate to zero freed all the tree,
                 * so we need to correct eh_depth
                 */
                err = ext4_ext_get_access(handle, inode, path);
                if (err == 0) {
                        ext_inode_hdr(inode)->eh_depth = 0;
                        ext_inode_hdr(inode)->eh_max =
                                cpu_to_le16(ext4_ext_space_root(inode));
                        err = ext4_ext_dirty(handle, inode, path);
                }
        }
out:
        ext4_ext_tree_changed(inode);
        ext4_ext_drop_refs(path);
        kfree(path);
        ext4_journal_stop(handle);

        return err;
}

/*
 * called at mount time
 */
void ext4_ext_init(struct super_block *sb)
{
        /*
         * possible initialization would be here
         */

        if (test_opt(sb, EXTENTS)) {
                printk("EXT4-fs: file extents enabled");
#ifdef AGGRESSIVE_TEST
                printk(", aggressive tests");
#endif
#ifdef CHECK_BINSEARCH
                printk(", check binsearch");
#endif
#ifdef EXTENTS_STATS
                printk(", stats");
#endif
                printk("\n");
#ifdef EXTENTS_STATS
                spin_lock_init(&EXT4_SB(sb)->s_ext_stats_lock);
                EXT4_SB(sb)->s_ext_min = 1 << 30;
                EXT4_SB(sb)->s_ext_max = 0;
#endif
        }
}

/*
 * called at umount time
 */
void ext4_ext_release(struct super_block *sb)
{
        if (!test_opt(sb, EXTENTS))
                return;

#ifdef EXTENTS_STATS
        if (EXT4_SB(sb)->s_ext_blocks && EXT4_SB(sb)->s_ext_extents) {
                struct ext4_sb_info *sbi = EXT4_SB(sb);
                printk(KERN_ERR "EXT4-fs: %lu blocks in %lu extents (%lu ave)\n",
                        sbi->s_ext_blocks, sbi->s_ext_extents,
                        sbi->s_ext_blocks / sbi->s_ext_extents);
                printk(KERN_ERR "EXT4-fs: extents: %lu min, %lu max, max depth %lu\n",
                        sbi->s_ext_min, sbi->s_ext_max, sbi->s_depth_max);
        }
#endif
}

/*
 * This function is called by ext4_ext_get_blocks() if someone tries to write
 * to an uninitialized extent. It may result in splitting the uninitialized
 * extent into multiple extents (upto three - one initialized and two
 * uninitialized).
 * There are three possibilities:
 *   a> There is no split required: Entire extent should be initialized
 *   b> Splits in two extents: Write is happening at either end of the extent
 *   c> Splits in three extents: Somone is writing in middle of the extent
 */
static int ext4_ext_convert_to_initialized(handle_t *handle,
                                                struct inode *inode,
                                                struct ext4_ext_path *path,
                                                ext4_lblk_t iblock,
                                                unsigned long max_blocks)
{
        struct ext4_extent *ex, newex;
        struct ext4_extent *ex1 = NULL;
        struct ext4_extent *ex2 = NULL;
        struct ext4_extent *ex3 = NULL;
        struct ext4_extent_header *eh;
        ext4_lblk_t ee_block;
        unsigned int allocated, ee_len, depth;
        ext4_fsblk_t newblock;
        int err = 0;
        int ret = 0;

        depth = ext_depth(inode);
        eh = path[depth].p_hdr;
        ex = path[depth].p_ext;
        ee_block = le32_to_cpu(ex->ee_block);
        ee_len = ext4_ext_get_actual_len(ex);
        allocated = ee_len - (iblock - ee_block);
        newblock = iblock - ee_block + ext_pblock(ex);
        ex2 = ex;

        /* ex1: ee_block to iblock - 1 : uninitialized */
        if (iblock > ee_block) {
                ex1 = ex;
                ex1->ee_len = cpu_to_le16(iblock - ee_block);
                ext4_ext_mark_uninitialized(ex1);
                ex2 = &newex;
        }
        /*
         * for sanity, update the length of the ex2 extent before
         * we insert ex3, if ex1 is NULL. This is to avoid temporary
         * overlap of blocks.
         */
        if (!ex1 && allocated > max_blocks)
                ex2->ee_len = cpu_to_le16(max_blocks);
        /* ex3: to ee_block + ee_len : uninitialised */
        if (allocated > max_blocks) {
                unsigned int newdepth;
                ex3 = &newex;
                ex3->ee_block = cpu_to_le32(iblock + max_blocks);
                ext4_ext_store_pblock(ex3, newblock + max_blocks);
                ex3->ee_len = cpu_to_le16(allocated - max_blocks);
                ext4_ext_mark_uninitialized(ex3);
                err = ext4_ext_insert_extent(handle, inode, path, ex3);
                if (err)
                        goto out;
                /*
                 * The depth, and hence eh & ex might change
                 * as part of the insert above.
                 */
                newdepth = ext_depth(inode);
                if (newdepth != depth) {
                        depth = newdepth;
                        path = ext4_ext_find_extent(inode, iblock, NULL);
                        if (IS_ERR(path)) {
                                err = PTR_ERR(path);
                                path = NULL;
                                goto out;
                        }
                        eh = path[depth].p_hdr;
                        ex = path[depth].p_ext;
                        if (ex2 != &newex)
                                ex2 = ex;
                }
                allocated = max_blocks;
        }
        /*
         * If there was a change of depth as part of the
         * insertion of ex3 above, we need to update the length
         * of the ex1 extent again here
         */
        if (ex1 && ex1 != ex) {
                ex1 = ex;
                ex1->ee_len = cpu_to_le16(iblock - ee_block);
                ext4_ext_mark_uninitialized(ex1);
                ex2 = &newex;
        }
        /* ex2: iblock to iblock + maxblocks-1 : initialised */
        ex2->ee_block = cpu_to_le32(iblock);
        ext4_ext_store_pblock(ex2, newblock);
        ex2->ee_len = cpu_to_le16(allocated);
        if (ex2 != ex)
                goto insert;
        err = ext4_ext_get_access(handle, inode, path + depth);
        if (err)
                goto out;
        /*
         * New (initialized) extent starts from the first block
         * in the current extent. i.e., ex2 == ex
         * We have to see if it can be merged with the extent
         * on the left.
         */
        if (ex2 > EXT_FIRST_EXTENT(eh)) {
                /*
                 * To merge left, pass "ex2 - 1" to try_to_merge(),
                 * since it merges towards right _only_.
                 */
                ret = ext4_ext_try_to_merge(inode, path, ex2 - 1);
                if (ret) {
                        err = ext4_ext_correct_indexes(handle, inode, path);
                        if (err)
                                goto out;
                        depth = ext_depth(inode);
                        ex2--;
                }
        }
        /*
         * Try to Merge towards right. This might be required
         * only when the whole extent is being written to.
         * i.e. ex2 == ex and ex3 == NULL.
         */
        if (!ex3) {
                ret = ext4_ext_try_to_merge(inode, path, ex2);
                if (ret) {
                        err = ext4_ext_correct_indexes(handle, inode, path);
                        if (err)
                                goto out;
                }
        }
        /* Mark modified extent as dirty */
        err = ext4_ext_dirty(handle, inode, path + depth);
        goto out;
insert:
        err = ext4_ext_insert_extent(handle, inode, path, &newex);
out:
        return err ? err : allocated;
}

int ext4_ext_get_blocks(handle_t *handle, struct inode *inode,
                        ext4_lblk_t iblock,
                        unsigned long max_blocks, struct buffer_head *bh_result,
                        int create, int extend_disksize)
{
        struct ext4_ext_path *path = NULL;
        struct ext4_extent_header *eh;
        struct ext4_extent newex, *ex;
        ext4_fsblk_t goal, newblock;
        int err = 0, depth, ret;
        unsigned long allocated = 0;

        __clear_bit(BH_New, &bh_result->b_state);
        ext_debug("blocks %u/%lu requested for inode %u\n",
                        iblock, max_blocks, inode->i_ino);
        mutex_lock(&EXT4_I(inode)->truncate_mutex);

        /* check in cache */
        goal = ext4_ext_in_cache(inode, iblock, &newex);
        if (goal) {
                if (goal == EXT4_EXT_CACHE_GAP) {
                        if (!create) {
                                /*
                                 * block isn't allocated yet and
                                 * user doesn't want to allocate it
                                 */
                                goto out2;
                        }
                        /* we should allocate requested block */
                } else if (goal == EXT4_EXT_CACHE_EXTENT) {
                        /* block is already allocated */
                        newblock = iblock
                                   - le32_to_cpu(newex.ee_block)
                                   + ext_pblock(&newex);
                        /* number of remaining blocks in the extent */
                        allocated = le16_to_cpu(newex.ee_len) -
                                        (iblock - le32_to_cpu(newex.ee_block));
                        goto out;
                } else {
                        BUG();
                }
        }

        /* find extent for this block */
        path = ext4_ext_find_extent(inode, iblock, NULL);
        if (IS_ERR(path)) {
                err = PTR_ERR(path);
                path = NULL;
                goto out2;
        }

        depth = ext_depth(inode);

        /*
         * consistent leaf must not be empty;
         * this situation is possible, though, _during_ tree modification;
         * this is why assert can't be put in ext4_ext_find_extent()
         */
        BUG_ON(path[depth].p_ext == NULL && depth != 0);
        eh = path[depth].p_hdr;

        ex = path[depth].p_ext;
        if (ex) {
                ext4_lblk_t ee_block = le32_to_cpu(ex->ee_block);
                ext4_fsblk_t ee_start = ext_pblock(ex);
                unsigned short ee_len;

                /*
                 * Uninitialized extents are treated as holes, except that
                 * we split out initialized portions during a write.
                 */
                ee_len = ext4_ext_get_actual_len(ex);
                /* if found extent covers block, simply return it */
                if (iblock >= ee_block && iblock < ee_block + ee_len) {
                        newblock = iblock - ee_block + ee_start;
                        /* number of remaining blocks in the extent */
                        allocated = ee_len - (iblock - ee_block);
                        ext_debug("%u fit into %lu:%d -> %llu\n", iblock,
                                        ee_block, ee_len, newblock);

                        /* Do not put uninitialized extent in the cache */
                        if (!ext4_ext_is_uninitialized(ex)) {
                                ext4_ext_put_in_cache(inode, ee_block,
                                                        ee_len, ee_start,
                                                        EXT4_EXT_CACHE_EXTENT);
                                goto out;
                        }
                        if (create == EXT4_CREATE_UNINITIALIZED_EXT)
                                goto out;
                        if (!create)
                                goto out2;

                        ret = ext4_ext_convert_to_initialized(handle, inode,
                                                                path, iblock,
                                                                max_blocks);
                        if (ret <= 0)
                                goto out2;
                        else
                                allocated = ret;
                        goto outnew;
                }
        }

        /*
         * requested block isn't allocated yet;
         * we couldn't try to create block if create flag is zero
         */
        if (!create) {
                /*
                 * put just found gap into cache to speed up
                 * subsequent requests
                 */
                ext4_ext_put_gap_in_cache(inode, path, iblock);
                goto out2;
        }
        /*
         * Okay, we need to do block allocation.  Lazily initialize the block
         * allocation info here if necessary.
         */
        if (S_ISREG(inode->i_mode) && (!EXT4_I(inode)->i_block_alloc_info))
                ext4_init_block_alloc_info(inode);

        /* allocate new block */
        goal = ext4_ext_find_goal(inode, path, iblock);

        /*
         * See if request is beyond maximum number of blocks we can have in
         * a single extent. For an initialized extent this limit is
         * EXT_INIT_MAX_LEN and for an uninitialized extent this limit is
         * EXT_UNINIT_MAX_LEN.
         */
        if (max_blocks > EXT_INIT_MAX_LEN &&
            create != EXT4_CREATE_UNINITIALIZED_EXT)
                max_blocks = EXT_INIT_MAX_LEN;
        else if (max_blocks > EXT_UNINIT_MAX_LEN &&
                 create == EXT4_CREATE_UNINITIALIZED_EXT)
                max_blocks = EXT_UNINIT_MAX_LEN;

        /* Check if we can really insert (iblock)::(iblock+max_blocks) extent */
        newex.ee_block = cpu_to_le32(iblock);
        newex.ee_len = cpu_to_le16(max_blocks);
        err = ext4_ext_check_overlap(inode, &newex, path);
        if (err)
                allocated = le16_to_cpu(newex.ee_len);
        else
                allocated = max_blocks;
        newblock = ext4_new_blocks(handle, inode, goal, &allocated, &err);
        if (!newblock)
                goto out2;
        ext_debug("allocate new block: goal %llu, found %llu/%lu\n",
                        goal, newblock, allocated);

        /* try to insert new extent into found leaf and return */
        ext4_ext_store_pblock(&newex, newblock);
        newex.ee_len = cpu_to_le16(allocated);
        if (create == EXT4_CREATE_UNINITIALIZED_EXT)  /* Mark uninitialized */
                ext4_ext_mark_uninitialized(&newex);
        err = ext4_ext_insert_extent(handle, inode, path, &newex);
        if (err) {
                /* free data blocks we just allocated */
                ext4_free_blocks(handle, inode, ext_pblock(&newex),
                                        le16_to_cpu(newex.ee_len));
                goto out2;
        }

        if (extend_disksize && inode->i_size > EXT4_I(inode)->i_disksize)
                EXT4_I(inode)->i_disksize = inode->i_size;

        /* previous routine could use block we allocated */
        newblock = ext_pblock(&newex);
outnew:
        __set_bit(BH_New, &bh_result->b_state);

        /* Cache only when it is _not_ an uninitialized extent */
        if (create != EXT4_CREATE_UNINITIALIZED_EXT)
                ext4_ext_put_in_cache(inode, iblock, allocated, newblock,
                                                EXT4_EXT_CACHE_EXTENT);
out:
        if (allocated > max_blocks)
                allocated = max_blocks;
        ext4_ext_show_leaf(inode, path);
        __set_bit(BH_Mapped, &bh_result->b_state);
        bh_result->b_bdev = inode->i_sb->s_bdev;
        bh_result->b_blocknr = newblock;
out2:
        if (path) {
                ext4_ext_drop_refs(path);
                kfree(path);
        }
        mutex_unlock(&EXT4_I(inode)->truncate_mutex);

        return err ? err : allocated;
}

void ext4_ext_truncate(struct inode * inode, struct page *page)
{
        struct address_space *mapping = inode->i_mapping;
        struct super_block *sb = inode->i_sb;
        ext4_lblk_t last_block;
        handle_t *handle;
        int err = 0;

        /*
         * probably first extent we're gonna free will be last in block
         */
        err = ext4_writepage_trans_blocks(inode) + 3;
        handle = ext4_journal_start(inode, err);
        if (IS_ERR(handle)) {
                if (page) {
                        clear_highpage(page);
                        flush_dcache_page(page);
                        unlock_page(page);
                        page_cache_release(page);
                }
                return;
        }

        if (page)
                ext4_block_truncate_page(handle, page, mapping, inode->i_size);

        mutex_lock(&EXT4_I(inode)->truncate_mutex);
        ext4_ext_invalidate_cache(inode);

        /*
         * TODO: optimization is possible here.
         * Probably we need not scan at all,
         * because page truncation is enough.
         */
        if (ext4_orphan_add(handle, inode))
                goto out_stop;

        /* we have to know where to truncate from in crash case */
        EXT4_I(inode)->i_disksize = inode->i_size;
        ext4_mark_inode_dirty(handle, inode);

        last_block = (inode->i_size + sb->s_blocksize - 1)
                        >> EXT4_BLOCK_SIZE_BITS(sb);
        err = ext4_ext_remove_space(inode, last_block);

        /* In a multi-transaction truncate, we only make the final
         * transaction synchronous.
         */
        if (IS_SYNC(inode))
                handle->h_sync = 1;

out_stop:
        /*
         * If this was a simple ftruncate() and the file will remain alive,
         * then we need to clear up the orphan record which we created above.
         * However, if this was a real unlink then we were called by
         * ext4_delete_inode(), and we allow that function to clean up the
         * orphan info for us.
         */
        if (inode->i_nlink)
                ext4_orphan_del(handle, inode);

        mutex_unlock(&EXT4_I(inode)->truncate_mutex);
        ext4_journal_stop(handle);
}

/*
 * ext4_ext_writepage_trans_blocks:
 * calculate max number of blocks we could modify
 * in order to allocate new block for an inode
 */
int ext4_ext_writepage_trans_blocks(struct inode *inode, int num)
{
        int needed;

        needed = ext4_ext_calc_credits_for_insert(inode, NULL);

        /* caller wants to allocate num blocks, but note it includes sb */
        needed = needed * num - (num - 1);

#ifdef CONFIG_QUOTA
        needed += 2 * EXT4_QUOTA_TRANS_BLOCKS(inode->i_sb);
#endif

        return needed;
}

/*
 * preallocate space for a file. This implements ext4's fallocate inode
 * operation, which gets called from sys_fallocate system call.
 * For block-mapped files, posix_fallocate should fall back to the method
 * of writing zeroes to the required new blocks (the same behavior which is
 * expected for file systems which do not support fallocate() system call).
 */
long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
{
        handle_t *handle;
        ext4_lblk_t block;
        unsigned long max_blocks;
        ext4_fsblk_t nblocks = 0;
        int ret = 0;
        int ret2 = 0;
        int retries = 0;
        struct buffer_head map_bh;
        unsigned int credits, blkbits = inode->i_blkbits;

        /*
         * currently supporting (pre)allocate mode for extent-based
         * files _only_
         */
        if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
                return -EOPNOTSUPP;

        /* preallocation to directories is currently not supported */
        if (S_ISDIR(inode->i_mode))
                return -ENODEV;

        block = offset >> blkbits;
        max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
                        - block;

        /*
         * credits to insert 1 extent into extent tree + buffers to be able to
         * modify 1 super block, 1 block bitmap and 1 group descriptor.
         */
        credits = EXT4_DATA_TRANS_BLOCKS(inode->i_sb) + 3;
retry:
        while (ret >= 0 && ret < max_blocks) {
                block = block + ret;
                max_blocks = max_blocks - ret;
                handle = ext4_journal_start(inode, credits);
                if (IS_ERR(handle)) {
                        ret = PTR_ERR(handle);
                        break;
                }

                ret = ext4_ext_get_blocks(handle, inode, block,
                                          max_blocks, &map_bh,
                                          EXT4_CREATE_UNINITIALIZED_EXT, 0);
                WARN_ON(!ret);
                if (!ret) {
                        ext4_error(inode->i_sb, "ext4_fallocate",
                                   "ext4_ext_get_blocks returned 0! inode#%lu"
                                   ", block=%u, max_blocks=%lu",
                                   inode->i_ino, block, max_blocks);
                        ret = -EIO;
                        ext4_mark_inode_dirty(handle, inode);
                        ret2 = ext4_journal_stop(handle);
                        break;
                }
                if (ret > 0) {
                        /* check wrap through sign-bit/zero here */
                        if ((block + ret) < 0 || (block + ret) < block) {
                                ret = -EIO;
                                ext4_mark_inode_dirty(handle, inode);
                                ret2 = ext4_journal_stop(handle);
                                break;
                        }
                        if (buffer_new(&map_bh) && ((block + ret) >
                            (EXT4_BLOCK_ALIGN(i_size_read(inode), blkbits)
                            >> blkbits)))
                                        nblocks = nblocks + ret;
                }

                /* Update ctime if new blocks get allocated */
                if (nblocks) {
                        struct timespec now;

                        now = current_fs_time(inode->i_sb);
                        if (!timespec_equal(&inode->i_ctime, &now))
                                inode->i_ctime = now;
                }

                ext4_mark_inode_dirty(handle, inode);
                ret2 = ext4_journal_stop(handle);
                if (ret2)
                        break;
        }

        if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
                goto retry;

        /*
         * Time to update the file size.
         * Update only when preallocation was requested beyond the file size.
         */
        if (!(mode & FALLOC_FL_KEEP_SIZE) &&
            (offset + len) > i_size_read(inode)) {
                if (ret > 0) {
                        /*
                         * if no error, we assume preallocation succeeded
                         * completely
                         */
                        mutex_lock(&inode->i_mutex);
                        i_size_write(inode, offset + len);
                        EXT4_I(inode)->i_disksize = i_size_read(inode);
                        mutex_unlock(&inode->i_mutex);
                } else if (ret < 0 && nblocks) {
                        /* Handle partial allocation scenario */
                        loff_t newsize;

                        mutex_lock(&inode->i_mutex);
                        newsize  = (nblocks << blkbits) + i_size_read(inode);
                        i_size_write(inode, EXT4_BLOCK_ALIGN(newsize, blkbits));
                        EXT4_I(inode)->i_disksize = i_size_read(inode);
                        mutex_unlock(&inode->i_mutex);
                }
        }

        return ret > 0 ? ret2 : ret;
}