/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 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., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/bio.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "print-tree.h"

#define MAX_CSUM_ITEMS(r, size) ((((BTRFS_LEAF_DATA_SIZE(r) - \
                                   sizeof(struct btrfs_item) * 2) / \
                                  size) - 1))

#define MAX_ORDERED_SUM_BYTES(r) ((PAGE_SIZE - \
                                   sizeof(struct btrfs_ordered_sum)) / \
                                   sizeof(struct btrfs_sector_sum) * \
                                   (r)->sectorsize - (r)->sectorsize)

int btrfs_insert_file_extent(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root,
                             u64 objectid, u64 pos,
                             u64 disk_offset, u64 disk_num_bytes,
                             u64 num_bytes, u64 offset, u64 ram_bytes,
                             u8 compression, u8 encryption, u16 other_encoding)
{
        int ret = 0;
        struct btrfs_file_extent_item *item;
        struct btrfs_key file_key;
        struct btrfs_path *path;
        struct extent_buffer *leaf;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        file_key.objectid = objectid;
        file_key.offset = pos;
        btrfs_set_key_type(&file_key, BTRFS_EXTENT_DATA_KEY);

        path->leave_spinning = 1;
        ret = btrfs_insert_empty_item(trans, root, path, &file_key,
                                      sizeof(*item));
        if (ret < 0)
                goto out;
        BUG_ON(ret);
        leaf = path->nodes[0];
        item = btrfs_item_ptr(leaf, path->slots[0],
                              struct btrfs_file_extent_item);
        btrfs_set_file_extent_disk_bytenr(leaf, item, disk_offset);
        btrfs_set_file_extent_disk_num_bytes(leaf, item, disk_num_bytes);
        btrfs_set_file_extent_offset(leaf, item, offset);
        btrfs_set_file_extent_num_bytes(leaf, item, num_bytes);
        btrfs_set_file_extent_ram_bytes(leaf, item, ram_bytes);
        btrfs_set_file_extent_generation(leaf, item, trans->transid);
        btrfs_set_file_extent_type(leaf, item, BTRFS_FILE_EXTENT_REG);
        btrfs_set_file_extent_compression(leaf, item, compression);
        btrfs_set_file_extent_encryption(leaf, item, encryption);
        btrfs_set_file_extent_other_encoding(leaf, item, other_encoding);

        btrfs_mark_buffer_dirty(leaf);
out:
        btrfs_free_path(path);
        return ret;
}

struct btrfs_csum_item *btrfs_lookup_csum(struct btrfs_trans_handle *trans,
                                          struct btrfs_root *root,
                                          struct btrfs_path *path,
                                          u64 bytenr, int cow)
{
        int ret;
        struct btrfs_key file_key;
        struct btrfs_key found_key;
        struct btrfs_csum_item *item;
        struct extent_buffer *leaf;
        u64 csum_offset = 0;
        u16 csum_size =
                btrfs_super_csum_size(&root->fs_info->super_copy);
        int csums_in_item;

        file_key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
        file_key.offset = bytenr;
        btrfs_set_key_type(&file_key, BTRFS_EXTENT_CSUM_KEY);
        ret = btrfs_search_slot(trans, root, &file_key, path, 0, cow);
        if (ret < 0)
                goto fail;
        leaf = path->nodes[0];
        if (ret > 0) {
                ret = 1;
                if (path->slots[0] == 0)
                        goto fail;
                path->slots[0]--;
                btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
                if (btrfs_key_type(&found_key) != BTRFS_EXTENT_CSUM_KEY)
                        goto fail;

                csum_offset = (bytenr - found_key.offset) >>
                                root->fs_info->sb->s_blocksize_bits;
                csums_in_item = btrfs_item_size_nr(leaf, path->slots[0]);
                csums_in_item /= csum_size;

                if (csum_offset >= csums_in_item) {
                        ret = -EFBIG;
                        goto fail;
                }
        }
        item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
        item = (struct btrfs_csum_item *)((unsigned char *)item +
                                          csum_offset * csum_size);
        return item;
fail:
        if (ret > 0)
                ret = -ENOENT;
        return ERR_PTR(ret);
}


int btrfs_lookup_file_extent(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root,
                             struct btrfs_path *path, u64 objectid,
                             u64 offset, int mod)
{
        int ret;
        struct btrfs_key file_key;
        int ins_len = mod < 0 ? -1 : 0;
        int cow = mod != 0;

        file_key.objectid = objectid;
        file_key.offset = offset;
        btrfs_set_key_type(&file_key, BTRFS_EXTENT_DATA_KEY);
        ret = btrfs_search_slot(trans, root, &file_key, path, ins_len, cow);
        return ret;
}


static int __btrfs_lookup_bio_sums(struct btrfs_root *root,
                                   struct inode *inode, struct bio *bio,
                                   u64 logical_offset, u32 *dst, int dio)
{
        u32 sum;
        struct bio_vec *bvec = bio->bi_io_vec;
        int bio_index = 0;
        u64 offset = 0;
        u64 item_start_offset = 0;
        u64 item_last_offset = 0;
        u64 disk_bytenr;
        u32 diff;
        u16 csum_size =
                btrfs_super_csum_size(&root->fs_info->super_copy);
        int ret;
        struct btrfs_path *path;
        struct btrfs_csum_item *item = NULL;
        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
        if (bio->bi_size > PAGE_CACHE_SIZE * 8)
                path->reada = 2;

        WARN_ON(bio->bi_vcnt <= 0);

        disk_bytenr = (u64)bio->bi_sector << 9;
        if (dio)
                offset = logical_offset;
        while (bio_index < bio->bi_vcnt) {
                if (!dio)
                        offset = page_offset(bvec->bv_page) + bvec->bv_offset;
                ret = btrfs_find_ordered_sum(inode, offset, disk_bytenr, &sum);
                if (ret == 0)
                        goto found;

                if (!item || disk_bytenr < item_start_offset ||
                    disk_bytenr >= item_last_offset) {
                        struct btrfs_key found_key;
                        u32 item_size;

                        if (item)
                                btrfs_release_path(root, path);
                        item = btrfs_lookup_csum(NULL, root->fs_info->csum_root,
                                                 path, disk_bytenr, 0);
                        if (IS_ERR(item)) {
                                ret = PTR_ERR(item);
                                if (ret == -ENOENT || ret == -EFBIG)
                                        ret = 0;
                                sum = 0;
                                if (BTRFS_I(inode)->root->root_key.objectid ==
                                    BTRFS_DATA_RELOC_TREE_OBJECTID) {
                                        set_extent_bits(io_tree, offset,
                                                offset + bvec->bv_len - 1,
                                                EXTENT_NODATASUM, GFP_NOFS);
                                } else {
                                        printk(KERN_INFO "btrfs no csum found "
                                               "for inode %lu start %llu\n",
                                               inode->i_ino,
                                               (unsigned long long)offset);
                                }
                                item = NULL;
                                btrfs_release_path(root, path);
                                goto found;
                        }
                        btrfs_item_key_to_cpu(path->nodes[0], &found_key,
                                              path->slots[0]);

                        item_start_offset = found_key.offset;
                        item_size = btrfs_item_size_nr(path->nodes[0],
                                                       path->slots[0]);
                        item_last_offset = item_start_offset +
                                (item_size / csum_size) *
                                root->sectorsize;
                        item = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                              struct btrfs_csum_item);
                }
                /*
                 * this byte range must be able to fit inside
                 * a single leaf so it will also fit inside a u32
                 */
                diff = disk_bytenr - item_start_offset;
                diff = diff / root->sectorsize;
                diff = diff * csum_size;

                read_extent_buffer(path->nodes[0], &sum,
                                   ((unsigned long)item) + diff,
                                   csum_size);
found:
                if (dst)
                        *dst++ = sum;
                else
                        set_state_private(io_tree, offset, sum);
                disk_bytenr += bvec->bv_len;
                offset += bvec->bv_len;
                bio_index++;
                bvec++;
        }
        btrfs_free_path(path);
        return 0;
}

int btrfs_lookup_bio_sums(struct btrfs_root *root, struct inode *inode,
                          struct bio *bio, u32 *dst)
{
        return __btrfs_lookup_bio_sums(root, inode, bio, 0, dst, 0);
}

int btrfs_lookup_bio_sums_dio(struct btrfs_root *root, struct inode *inode,
                              struct bio *bio, u64 offset, u32 *dst)
{
        return __btrfs_lookup_bio_sums(root, inode, bio, offset, dst, 1);
}

int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
                             struct list_head *list)
{
        struct btrfs_key key;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_ordered_sum *sums;
        struct btrfs_sector_sum *sector_sum;
        struct btrfs_csum_item *item;
        unsigned long offset;
        int ret;
        size_t size;
        u64 csum_end;
        u16 csum_size = btrfs_super_csum_size(&root->fs_info->super_copy);

        path = btrfs_alloc_path();
        BUG_ON(!path);

        key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
        key.offset = start;
        key.type = BTRFS_EXTENT_CSUM_KEY;

        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto fail;
        if (ret > 0 && path->slots[0] > 0) {
                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &key, path->slots[0] - 1);
                if (key.objectid == BTRFS_EXTENT_CSUM_OBJECTID &&
                    key.type == BTRFS_EXTENT_CSUM_KEY) {
                        offset = (start - key.offset) >>
                                 root->fs_info->sb->s_blocksize_bits;
                        if (offset * csum_size <
                            btrfs_item_size_nr(leaf, path->slots[0] - 1))
                                path->slots[0]--;
                }
        }

        while (start <= end) {
                leaf = path->nodes[0];
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret < 0)
                                goto fail;
                        if (ret > 0)
                                break;
                        leaf = path->nodes[0];
                }

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
                    key.type != BTRFS_EXTENT_CSUM_KEY)
                        break;

                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                if (key.offset > end)
                        break;

                if (key.offset > start)
                        start = key.offset;

                size = btrfs_item_size_nr(leaf, path->slots[0]);
                csum_end = key.offset + (size / csum_size) * root->sectorsize;
                if (csum_end <= start) {
                        path->slots[0]++;
                        continue;
                }

                csum_end = min(csum_end, end + 1);
                item = btrfs_item_ptr(path->nodes[0], path->slots[0],
                                      struct btrfs_csum_item);
                while (start < csum_end) {
                        size = min_t(size_t, csum_end - start,
                                        MAX_ORDERED_SUM_BYTES(root));
                        sums = kzalloc(btrfs_ordered_sum_size(root, size),
                                        GFP_NOFS);
                        BUG_ON(!sums);

                        sector_sum = sums->sums;
                        sums->bytenr = start;
                        sums->len = size;

                        offset = (start - key.offset) >>
                                root->fs_info->sb->s_blocksize_bits;
                        offset *= csum_size;

                        while (size > 0) {
                                read_extent_buffer(path->nodes[0],
                                                &sector_sum->sum,
                                                ((unsigned long)item) +
                                                offset, csum_size);
                                sector_sum->bytenr = start;

                                size -= root->sectorsize;
                                start += root->sectorsize;
                                offset += csum_size;
                                sector_sum++;
                        }
                        list_add_tail(&sums->list, list);
                }
                path->slots[0]++;
        }
        ret = 0;
fail:
        btrfs_free_path(path);
        return ret;
}

int btrfs_csum_one_bio(struct btrfs_root *root, struct inode *inode,
                       struct bio *bio, u64 file_start, int contig)
{
        struct btrfs_ordered_sum *sums;
        struct btrfs_sector_sum *sector_sum;
        struct btrfs_ordered_extent *ordered;
        char *data;
        struct bio_vec *bvec = bio->bi_io_vec;
        int bio_index = 0;
        unsigned long total_bytes = 0;
        unsigned long this_sum_bytes = 0;
        u64 offset;
        u64 disk_bytenr;

        WARN_ON(bio->bi_vcnt <= 0);
        sums = kzalloc(btrfs_ordered_sum_size(root, bio->bi_size), GFP_NOFS);
        if (!sums)
                return -ENOMEM;

        sector_sum = sums->sums;
        disk_bytenr = (u64)bio->bi_sector << 9;
        sums->len = bio->bi_size;
        INIT_LIST_HEAD(&sums->list);

        if (contig)
                offset = file_start;
        else
                offset = page_offset(bvec->bv_page) + bvec->bv_offset;

        ordered = btrfs_lookup_ordered_extent(inode, offset);
        BUG_ON(!ordered);
        sums->bytenr = ordered->start;

        while (bio_index < bio->bi_vcnt) {
                if (!contig)
                        offset = page_offset(bvec->bv_page) + bvec->bv_offset;

                if (!contig && (offset >= ordered->file_offset + ordered->len ||
                    offset < ordered->file_offset)) {
                        unsigned long bytes_left;
                        sums->len = this_sum_bytes;
                        this_sum_bytes = 0;
                        btrfs_add_ordered_sum(inode, ordered, sums);
                        btrfs_put_ordered_extent(ordered);

                        bytes_left = bio->bi_size - total_bytes;

                        sums = kzalloc(btrfs_ordered_sum_size(root, bytes_left),
                                       GFP_NOFS);
                        BUG_ON(!sums);
                        sector_sum = sums->sums;
                        sums->len = bytes_left;
                        ordered = btrfs_lookup_ordered_extent(inode, offset);
                        BUG_ON(!ordered);
                        sums->bytenr = ordered->start;
                }

                data = kmap_atomic(bvec->bv_page, KM_USER0);
                sector_sum->sum = ~(u32)0;
                sector_sum->sum = btrfs_csum_data(root,
                                                  data + bvec->bv_offset,
                                                  sector_sum->sum,
                                                  bvec->bv_len);
                kunmap_atomic(data, KM_USER0);
                btrfs_csum_final(sector_sum->sum,
                                 (char *)&sector_sum->sum);
                sector_sum->bytenr = disk_bytenr;

                sector_sum++;
                bio_index++;
                total_bytes += bvec->bv_len;
                this_sum_bytes += bvec->bv_len;
                disk_bytenr += bvec->bv_len;
                offset += bvec->bv_len;
                bvec++;
        }
        this_sum_bytes = 0;
        btrfs_add_ordered_sum(inode, ordered, sums);
        btrfs_put_ordered_extent(ordered);
        return 0;
}

/*
 * helper function for csum removal, this expects the
 * key to describe the csum pointed to by the path, and it expects
 * the csum to overlap the range [bytenr, len]
 *
 * The csum should not be entirely contained in the range and the
 * range should not be entirely contained in the csum.
 *
 * This calls btrfs_truncate_item with the correct args based on the
 * overlap, and fixes up the key as required.
 */
static noinline int truncate_one_csum(struct btrfs_trans_handle *trans,
                                      struct btrfs_root *root,
                                      struct btrfs_path *path,
                                      struct btrfs_key *key,
                                      u64 bytenr, u64 len)
{
        struct extent_buffer *leaf;
        u16 csum_size =
                btrfs_super_csum_size(&root->fs_info->super_copy);
        u64 csum_end;
        u64 end_byte = bytenr + len;
        u32 blocksize_bits = root->fs_info->sb->s_blocksize_bits;
        int ret;

        leaf = path->nodes[0];
        csum_end = btrfs_item_size_nr(leaf, path->slots[0]) / csum_size;
        csum_end <<= root->fs_info->sb->s_blocksize_bits;
        csum_end += key->offset;

        if (key->offset < bytenr && csum_end <= end_byte) {
                /*
                 *         [ bytenr - len ]
                 *         [   ]
                 *   [csum     ]
                 *   A simple truncate off the end of the item
                 */
                u32 new_size = (bytenr - key->offset) >> blocksize_bits;
                new_size *= csum_size;
                ret = btrfs_truncate_item(trans, root, path, new_size, 1);
                BUG_ON(ret);
        } else if (key->offset >= bytenr && csum_end > end_byte &&
                   end_byte > key->offset) {
                /*
                 *         [ bytenr - len ]
                 *                 [ ]
                 *                 [csum     ]
                 * we need to truncate from the beginning of the csum
                 */
                u32 new_size = (csum_end - end_byte) >> blocksize_bits;
                new_size *= csum_size;

                ret = btrfs_truncate_item(trans, root, path, new_size, 0);
                BUG_ON(ret);

                key->offset = end_byte;
                ret = btrfs_set_item_key_safe(trans, root, path, key);
                BUG_ON(ret);
        } else {
                BUG();
        }
        return 0;
}

/*
 * deletes the csum items from the csum tree for a given
 * range of bytes.
 */
int btrfs_del_csums(struct btrfs_trans_handle *trans,
                    struct btrfs_root *root, u64 bytenr, u64 len)
{
        struct btrfs_path *path;
        struct btrfs_key key;
        u64 end_byte = bytenr + len;
        u64 csum_end;
        struct extent_buffer *leaf;
        int ret;
        u16 csum_size =
                btrfs_super_csum_size(&root->fs_info->super_copy);
        int blocksize_bits = root->fs_info->sb->s_blocksize_bits;

        root = root->fs_info->csum_root;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        while (1) {
                key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
                key.offset = end_byte - 1;
                key.type = BTRFS_EXTENT_CSUM_KEY;

                path->leave_spinning = 1;
                ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
                if (ret > 0) {
                        if (path->slots[0] == 0)
                                goto out;
                        path->slots[0]--;
                } else if (ret < 0) {
                        goto out;
                }

                leaf = path->nodes[0];
                btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);

                if (key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
                    key.type != BTRFS_EXTENT_CSUM_KEY) {
                        break;
                }

                if (key.offset >= end_byte)
                        break;

                csum_end = btrfs_item_size_nr(leaf, path->slots[0]) / csum_size;
                csum_end <<= blocksize_bits;
                csum_end += key.offset;

                /* this csum ends before we start, we're done */
                if (csum_end <= bytenr)
                        break;

                /* delete the entire item, it is inside our range */
                if (key.offset >= bytenr && csum_end <= end_byte) {
                        ret = btrfs_del_item(trans, root, path);
                        BUG_ON(ret);
                        if (key.offset == bytenr)
                                break;
                } else if (key.offset < bytenr && csum_end > end_byte) {
                        unsigned long offset;
                        unsigned long shift_len;
                        unsigned long item_offset;
                        /*
                         *        [ bytenr - len ]
                         *     [csum                ]
                         *
                         * Our bytes are in the middle of the csum,
                         * we need to split this item and insert a new one.
                         *
                         * But we can't drop the path because the
                         * csum could change, get removed, extended etc.
                         *
                         * The trick here is the max size of a csum item leaves
                         * enough room in the tree block for a single
                         * item header.  So, we split the item in place,
                         * adding a new header pointing to the existing
                         * bytes.  Then we loop around again and we have
                         * a nicely formed csum item that we can neatly
                         * truncate.
                         */
                        offset = (bytenr - key.offset) >> blocksize_bits;
                        offset *= csum_size;

                        shift_len = (len >> blocksize_bits) * csum_size;

                        item_offset = btrfs_item_ptr_offset(leaf,
                                                            path->slots[0]);

                        memset_extent_buffer(leaf, 0, item_offset + offset,
                                             shift_len);
                        key.offset = bytenr;

                        /*
                         * btrfs_split_item returns -EAGAIN when the
                         * item changed size or key
                         */
                        ret = btrfs_split_item(trans, root, path, &key, offset);
                        BUG_ON(ret && ret != -EAGAIN);

                        key.offset = end_byte - 1;
                } else {
                        ret = truncate_one_csum(trans, root, path,
                                                &key, bytenr, len);
                        BUG_ON(ret);
                        if (key.offset < bytenr)
                                break;
                }
                btrfs_release_path(root, path);
        }
out:
        btrfs_free_path(path);
        return 0;
}

int btrfs_csum_file_blocks(struct btrfs_trans_handle *trans,
                           struct btrfs_root *root,
                           struct btrfs_ordered_sum *sums)
{
        u64 bytenr;
        int ret;
        struct btrfs_key file_key;
        struct btrfs_key found_key;
        u64 next_offset;
        u64 total_bytes = 0;
        int found_next;
        struct btrfs_path *path;
        struct btrfs_csum_item *item;
        struct btrfs_csum_item *item_end;
        struct extent_buffer *leaf = NULL;
        u64 csum_offset;
        struct btrfs_sector_sum *sector_sum;
        u32 nritems;
        u32 ins_size;
        char *eb_map;
        char *eb_token;
        unsigned long map_len;
        unsigned long map_start;
        u16 csum_size =
                btrfs_super_csum_size(&root->fs_info->super_copy);

        path = btrfs_alloc_path();
        BUG_ON(!path);
        sector_sum = sums->sums;
again:
        next_offset = (u64)-1;
        found_next = 0;
        file_key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
        file_key.offset = sector_sum->bytenr;
        bytenr = sector_sum->bytenr;
        btrfs_set_key_type(&file_key, BTRFS_EXTENT_CSUM_KEY);

        item = btrfs_lookup_csum(trans, root, path, sector_sum->bytenr, 1);
        if (!IS_ERR(item)) {
                leaf = path->nodes[0];
                ret = 0;
                goto found;
        }
        ret = PTR_ERR(item);
        if (ret != -EFBIG && ret != -ENOENT)
                goto fail_unlock;

        if (ret == -EFBIG) {
                u32 item_size;
                /* we found one, but it isn't big enough yet */
                leaf = path->nodes[0];
                item_size = btrfs_item_size_nr(leaf, path->slots[0]);
                if ((item_size / csum_size) >=
                    MAX_CSUM_ITEMS(root, csum_size)) {
                        /* already at max size, make a new one */
                        goto insert;
                }
        } else {
                int slot = path->slots[0] + 1;
                /* we didn't find a csum item, insert one */
                nritems = btrfs_header_nritems(path->nodes[0]);
                if (path->slots[0] >= nritems - 1) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret == 1)
                                found_next = 1;
                        if (ret != 0)
                                goto insert;
                        slot = 0;
                }
                btrfs_item_key_to_cpu(path->nodes[0], &found_key, slot);
                if (found_key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
                    found_key.type != BTRFS_EXTENT_CSUM_KEY) {
                        found_next = 1;
                        goto insert;
                }
                next_offset = found_key.offset;
                found_next = 1;
                goto insert;
        }

        /*
         * at this point, we know the tree has an item, but it isn't big
         * enough yet to put our csum in.  Grow it
         */
        btrfs_release_path(root, path);
        ret = btrfs_search_slot(trans, root, &file_key, path,
                                csum_size, 1);
        if (ret < 0)
                goto fail_unlock;

        if (ret > 0) {
                if (path->slots[0] == 0)
                        goto insert;
                path->slots[0]--;
        }

        leaf = path->nodes[0];
        btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
        csum_offset = (bytenr - found_key.offset) >>
                        root->fs_info->sb->s_blocksize_bits;

        if (btrfs_key_type(&found_key) != BTRFS_EXTENT_CSUM_KEY ||
            found_key.objectid != BTRFS_EXTENT_CSUM_OBJECTID ||
            csum_offset >= MAX_CSUM_ITEMS(root, csum_size)) {
                goto insert;
        }

        if (csum_offset >= btrfs_item_size_nr(leaf, path->slots[0]) /
            csum_size) {
                u32 diff = (csum_offset + 1) * csum_size;

                /*
                 * is the item big enough already?  we dropped our lock
                 * before and need to recheck
                 */
                if (diff < btrfs_item_size_nr(leaf, path->slots[0]))
                        goto csum;

                diff = diff - btrfs_item_size_nr(leaf, path->slots[0]);
                if (diff != csum_size)
                        goto insert;

                ret = btrfs_extend_item(trans, root, path, diff);
                BUG_ON(ret);
                goto csum;
        }

insert:
        btrfs_release_path(root, path);
        csum_offset = 0;
        if (found_next) {
                u64 tmp = total_bytes + root->sectorsize;
                u64 next_sector = sector_sum->bytenr;
                struct btrfs_sector_sum *next = sector_sum + 1;

                while (tmp < sums->len) {
                        if (next_sector + root->sectorsize != next->bytenr)
                                break;
                        tmp += root->sectorsize;
                        next_sector = next->bytenr;
                        next++;
                }
                tmp = min(tmp, next_offset - file_key.offset);
                tmp >>= root->fs_info->sb->s_blocksize_bits;
                tmp = max((u64)1, tmp);
                tmp = min(tmp, (u64)MAX_CSUM_ITEMS(root, csum_size));
                ins_size = csum_size * tmp;
        } else {
                ins_size = csum_size;
        }
        path->leave_spinning = 1;
        ret = btrfs_insert_empty_item(trans, root, path, &file_key,
                                      ins_size);
        path->leave_spinning = 0;
        if (ret < 0)
                goto fail_unlock;
        if (ret != 0) {
                WARN_ON(1);
                goto fail_unlock;
        }
csum:
        leaf = path->nodes[0];
        item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
        ret = 0;
        item = (struct btrfs_csum_item *)((unsigned char *)item +
                                          csum_offset * csum_size);
found:
        item_end = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
        item_end = (struct btrfs_csum_item *)((unsigned char *)item_end +
                                      btrfs_item_size_nr(leaf, path->slots[0]));
        eb_token = NULL;
next_sector:

        if (!eb_token ||
           (unsigned long)item + csum_size >= map_start + map_len) {
                int err;

                if (eb_token)
                        unmap_extent_buffer(leaf, eb_token, KM_USER1);
                eb_token = NULL;
                err = map_private_extent_buffer(leaf, (unsigned long)item,
                                                csum_size,
                                                &eb_token, &eb_map,
                                                &map_start, &map_len, KM_USER1);
                if (err)
                        eb_token = NULL;
        }
        if (eb_token) {
                memcpy(eb_token + ((unsigned long)item & (PAGE_CACHE_SIZE - 1)),
                       &sector_sum->sum, csum_size);
        } else {
                write_extent_buffer(leaf, &sector_sum->sum,
                                    (unsigned long)item, csum_size);
        }

        total_bytes += root->sectorsize;
        sector_sum++;
        if (total_bytes < sums->len) {
                item = (struct btrfs_csum_item *)((char *)item +
                                                  csum_size);
                if (item < item_end && bytenr + PAGE_CACHE_SIZE ==
                    sector_sum->bytenr) {
                        bytenr = sector_sum->bytenr;
                        goto next_sector;
                }
        }
        if (eb_token) {
                unmap_extent_buffer(leaf, eb_token, KM_USER1);
                eb_token = NULL;
        }
        btrfs_mark_buffer_dirty(path->nodes[0]);
        if (total_bytes < sums->len) {
                btrfs_release_path(root, path);
                cond_resched();
                goto again;
        }
out:
        btrfs_free_path(path);
        return ret;

fail_unlock:
        goto out;
}