file-item.c

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/*
 * 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) ((unsigned long)(((BTRFS_LEAF_DATA_SIZE(r) - \
                   sizeof(struct btrfs_item) * 2) / \
                  size) - 1))

#define MAX_CSUM_ITEMS(r, size) (min_t(u32, __MAX_CSUM_ITEMS(r, size), \
                       PAGE_CACHE_SIZE))

#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); /* Can't happen */
    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);

    /*
     * the free space stuff is only read when it hasn't been
     * updated in the current transaction.  So, we can safely
     * read from the commit root and sidestep a nasty deadlock
     * between reading the free space cache and updating the csum tree.
     */
    if (btrfs_is_free_space_inode(inode)) {
        path->search_commit_root = 1;
        path->skip_locking = 1;
    }

    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(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 %llu start %llu\n",
                           (unsigned long long)
                           btrfs_ino(inode),
                           (unsigned long long)offset);
                }
                item = NULL;
                btrfs_release_path(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)
{
    return __btrfs_lookup_bio_sums(root, inode, bio, offset, NULL, 1);
}

int btrfs_lookup_csums_range(struct btrfs_root *root, u64 start, u64 end,
                 struct list_head *list, int search_commit)
{
    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;
    LIST_HEAD(tmplist);
    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();
    if (!path)
        return -ENOMEM;

    if (search_commit) {
        path->skip_locking = 1;
        path->reada = 2;
        path->search_commit_root = 1;
    }

    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);
            if (!sums) {
                ret = -ENOMEM;
                goto fail;
            }

            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, &tmplist);
        }
        path->slots[0]++;
    }
    ret = 0;
fail:
    while (ret < 0 && !list_empty(&tmplist)) {
        sums = list_entry(&tmplist, struct btrfs_ordered_sum, list);
        list_del(&sums->list);
        kfree(sums);
    }
    list_splice_tail(&tmplist, list);

    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); /* Logic error */
    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); /* -ENOMEM */
            sector_sum = sums->sums;
            sums->len = bytes_left;
            ordered = btrfs_lookup_ordered_extent(inode, offset);
            BUG_ON(!ordered); /* Logic error */
            sums->bytenr = ordered->start;
        }

        data = kmap_atomic(bvec->bv_page);
        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);
        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 void 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;

    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;
        btrfs_truncate_item(trans, root, path, new_size, 1);
    } 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;

        btrfs_truncate_item(trans, root, path, new_size, 0);

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

/*
 * 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)
                break;
            path->slots[0]--;
        } else 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;
        }

        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);
            if (ret)
                goto out;
            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);
            if (ret && ret != -EAGAIN) {
                btrfs_abort_transaction(trans, root, ret);
                goto out;
            }

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

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;
    u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);

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

    sector_sum = sums->sums;
    trans->adding_csums = 1;
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(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;

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

insert:
    btrfs_release_path(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]));
next_sector:

    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;
        }
    }

    btrfs_mark_buffer_dirty(path->nodes[0]);
    if (total_bytes < sums->len) {
        btrfs_release_path(path);
        cond_resched();
        goto again;
    }
out:
    trans->adding_csums = 0;
    btrfs_free_path(path);
    return ret;

fail_unlock:
    goto out;
}