/*
 * 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 "volumes.h"
#include "print-tree.h"
#include "compression.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_SIZE))

#define MAX_ORDERED_SUM_BYTES(r) ((PAGE_SIZE - \
                                   sizeof(struct btrfs_ordered_sum)) / \
                                   sizeof(u32) * (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;
        file_key.type = 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;
}

static 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;
        file_key.type = 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 (found_key.type != 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;
                } else if (csum_offset > csums_in_item) {
                        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;
        file_key.type = BTRFS_EXTENT_DATA_KEY;
        ret = btrfs_search_slot(trans, root, &file_key, path, ins_len, cow);
        return ret;
}

static void btrfs_io_bio_endio_readpage(struct btrfs_io_bio *bio, int err)
{
        kfree(bio->csum_allocated);
}

static int __btrfs_lookup_bio_sums(struct btrfs_root *root,
                                   struct inode *inode, struct bio *bio,
                                   u64 logical_offset, u32 *dst, int dio)
{
        struct bio_vec *bvec = bio->bi_io_vec;
        struct btrfs_io_bio *btrfs_bio = btrfs_io_bio(bio);
        struct btrfs_csum_item *item = NULL;
        struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
        struct btrfs_path *path;
        u8 *csum;
        u64 offset = 0;
        u64 item_start_offset = 0;
        u64 item_last_offset = 0;
        u64 disk_bytenr;
        u64 page_bytes_left;
        u32 diff;
        int nblocks;
        int bio_index = 0;
        int count;
        u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);

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

        nblocks = bio->bi_iter.bi_size >> inode->i_sb->s_blocksize_bits;
        if (!dst) {
                if (nblocks * csum_size > BTRFS_BIO_INLINE_CSUM_SIZE) {
                        btrfs_bio->csum_allocated = kmalloc_array(nblocks,
                                        csum_size, GFP_NOFS);
                        if (!btrfs_bio->csum_allocated) {
                                btrfs_free_path(path);
                                return -ENOMEM;
                        }
                        btrfs_bio->csum = btrfs_bio->csum_allocated;
                        btrfs_bio->end_io = btrfs_io_bio_endio_readpage;
                } else {
                        btrfs_bio->csum = btrfs_bio->csum_inline;
                }
                csum = btrfs_bio->csum;
        } else {
                csum = (u8 *)dst;
        }

        if (bio->bi_iter.bi_size > PAGE_SIZE * 8)
                path->reada = READA_FORWARD;

        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_iter.bi_sector << 9;
        if (dio)
                offset = logical_offset;

        page_bytes_left = bvec->bv_len;
        while (bio_index < bio->bi_vcnt) {
                if (!dio)
                        offset = page_offset(bvec->bv_page) + bvec->bv_offset;
                count = btrfs_find_ordered_sum(inode, offset, disk_bytenr,
                                               (u32 *)csum, nblocks);
                if (count)
                        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)) {
                                count = 1;
                                memset(csum, 0, csum_size);
                                if (BTRFS_I(inode)->root->root_key.objectid ==
                                    BTRFS_DATA_RELOC_TREE_OBJECTID) {
                                        set_extent_bits(io_tree, offset,
                                                offset + root->sectorsize - 1,
                                                EXTENT_NODATASUM, GFP_NOFS);
                                } else {
                                        btrfs_info(BTRFS_I(inode)->root->fs_info,
                                                   "no csum found for inode %llu start %llu",
                                               btrfs_ino(inode), 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;
                count = min_t(int, nblocks, (item_last_offset - disk_bytenr) >>
                                            inode->i_sb->s_blocksize_bits);
                read_extent_buffer(path->nodes[0], csum,
                                   ((unsigned long)item) + diff,
                                   csum_size * count);
found:
                csum += count * csum_size;
                nblocks -= count;

                while (count--) {
                        disk_bytenr += root->sectorsize;
                        offset += root->sectorsize;
                        page_bytes_left -= root->sectorsize;
                        if (!page_bytes_left) {
                                bio_index++;
                                /*
                                 * make sure we're still inside the
                                 * bio before we update page_bytes_left
                                 */
                                if (bio_index >= bio->bi_vcnt) {
                                        WARN_ON_ONCE(count);
                                        goto done;
                                }
                                bvec++;
                                page_bytes_left = bvec->bv_len;
                        }

                }
        }

done:
        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_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);

        ASSERT(IS_ALIGNED(start, root->sectorsize) &&
               IS_ALIGNED(end + 1, root->sectorsize));

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

        if (search_commit) {
                path->skip_locking = 1;
                path->reada = READA_FORWARD;
                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 ||
                    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;
                        }

                        sums->bytenr = start;
                        sums->len = (int)size;

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

                        read_extent_buffer(path->nodes[0],
                                           sums->sums,
                                           ((unsigned long)item) + offset,
                                           csum_size * size);

                        start += root->sectorsize * size;
                        list_add_tail(&sums->list, &tmplist);
                }
                path->slots[0]++;
        }
        ret = 0;
fail:
        while (ret < 0 && !list_empty(&tmplist)) {
                sums = list_entry(tmplist.next, 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_ordered_extent *ordered;
        char *data;
        struct bio_vec *bvec = bio->bi_io_vec;
        int bio_index = 0;
        int index;
        int nr_sectors;
        int i;
        unsigned long total_bytes = 0;
        unsigned long this_sum_bytes = 0;
        u64 offset;

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

        sums->len = bio->bi_iter.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 = (u64)bio->bi_iter.bi_sector << 9;
        index = 0;

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

                data = kmap_atomic(bvec->bv_page);

                nr_sectors = BTRFS_BYTES_TO_BLKS(root->fs_info,
                                                bvec->bv_len + root->sectorsize
                                                - 1);

                for (i = 0; i < nr_sectors; i++) {
                        if (offset >= ordered->file_offset + ordered->len ||
                                offset < ordered->file_offset) {
                                unsigned long bytes_left;

                                kunmap_atomic(data);
                                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_iter.bi_size - total_bytes;

                                sums = kzalloc(btrfs_ordered_sum_size(root, bytes_left),
                                        GFP_NOFS);
                                BUG_ON(!sums); /* -ENOMEM */
                                sums->len = bytes_left;
                                ordered = btrfs_lookup_ordered_extent(inode,
                                                                offset);
                                ASSERT(ordered); /* Logic error */
                                sums->bytenr = ((u64)bio->bi_iter.bi_sector << 9)
                                        + total_bytes;
                                index = 0;

                                data = kmap_atomic(bvec->bv_page);
                        }

                        sums->sums[index] = ~(u32)0;
                        sums->sums[index]
                                = btrfs_csum_data(data + bvec->bv_offset
                                                + (i * root->sectorsize),
                                                sums->sums[index],
                                                root->sectorsize);
                        btrfs_csum_final(sums->sums[index],
                                        (char *)(sums->sums + index));
                        index++;
                        offset += root->sectorsize;
                        this_sum_bytes += root->sectorsize;
                        total_bytes += root->sectorsize;
                }

                kunmap_atomic(data);

                bio_index++;
                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_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(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(root, path, new_size, 0);

                key->offset = end_byte;
                btrfs_set_item_key_safe(root->fs_info, 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(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)
{
        struct btrfs_key file_key;
        struct btrfs_key found_key;
        struct btrfs_path *path;
        struct btrfs_csum_item *item;
        struct btrfs_csum_item *item_end;
        struct extent_buffer *leaf = NULL;
        u64 next_offset;
        u64 total_bytes = 0;
        u64 csum_offset;
        u64 bytenr;
        u32 nritems;
        u32 ins_size;
        int index = 0;
        int found_next;
        int ret;
        u16 csum_size = btrfs_super_csum_size(root->fs_info->super_copy);

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
again:
        next_offset = (u64)-1;
        found_next = 0;
        bytenr = sums->bytenr + total_bytes;
        file_key.objectid = BTRFS_EXTENT_CSUM_OBJECTID;
        file_key.offset = bytenr;
        file_key.type = BTRFS_EXTENT_CSUM_KEY;

        item = btrfs_lookup_csum(trans, root, path, bytenr, 1);
        if (!IS_ERR(item)) {
                ret = 0;
                leaf = path->nodes[0];
                item_end = btrfs_item_ptr(leaf, path->slots[0],
                                          struct btrfs_csum_item);
                item_end = (struct btrfs_csum_item *)((char *)item_end +
                           btrfs_item_size_nr(leaf, path->slots[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 (!nritems || (path->slots[0] >= nritems - 1)) {
                        ret = btrfs_next_leaf(root, path);
                        if (ret == 1)
                                found_next = 1;
                        if (ret != 0)
                                goto insert;
                        slot = path->slots[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 (found_key.type != 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) {
                int extend_nr;
                u64 tmp;
                u32 diff;
                u32 free_space;

                if (btrfs_leaf_free_space(root, leaf) <
                                 sizeof(struct btrfs_item) + csum_size * 2)
                        goto insert;

                free_space = btrfs_leaf_free_space(root, leaf) -
                                         sizeof(struct btrfs_item) - csum_size;
                tmp = sums->len - total_bytes;
                tmp >>= root->fs_info->sb->s_blocksize_bits;
                WARN_ON(tmp < 1);

                extend_nr = max_t(int, 1, (int)tmp);
                diff = (csum_offset + extend_nr) * csum_size;
                diff = min(diff, MAX_CSUM_ITEMS(root, csum_size) * csum_size);

                diff = diff - btrfs_item_size_nr(leaf, path->slots[0]);
                diff = min(free_space, diff);
                diff /= csum_size;
                diff *= csum_size;

                btrfs_extend_item(root, path, diff);
                ret = 0;
                goto csum;
        }

insert:
        btrfs_release_path(path);
        csum_offset = 0;
        if (found_next) {
                u64 tmp;

                tmp = sums->len - total_bytes;
                tmp >>= root->fs_info->sb->s_blocksize_bits;
                tmp = min(tmp, (next_offset - file_key.offset) >>
                                         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 (WARN_ON(ret != 0))
                goto fail_unlock;
        leaf = path->nodes[0];
csum:
        item = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_csum_item);
        item_end = (struct btrfs_csum_item *)((unsigned char *)item +
                                      btrfs_item_size_nr(leaf, path->slots[0]));
        item = (struct btrfs_csum_item *)((unsigned char *)item +
                                          csum_offset * csum_size);
found:
        ins_size = (u32)(sums->len - total_bytes) >>
                   root->fs_info->sb->s_blocksize_bits;
        ins_size *= csum_size;
        ins_size = min_t(u32, (unsigned long)item_end - (unsigned long)item,
                              ins_size);
        write_extent_buffer(leaf, sums->sums + index, (unsigned long)item,
                            ins_size);

        ins_size /= csum_size;
        total_bytes += ins_size * root->sectorsize;
        index += ins_size;

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

fail_unlock:
        goto out;
}

void btrfs_extent_item_to_extent_map(struct inode *inode,
                                     const struct btrfs_path *path,
                                     struct btrfs_file_extent_item *fi,
                                     const bool new_inline,
                                     struct extent_map *em)
{
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct extent_buffer *leaf = path->nodes[0];
        const int slot = path->slots[0];
        struct btrfs_key key;
        u64 extent_start, extent_end;
        u64 bytenr;
        u8 type = btrfs_file_extent_type(leaf, fi);
        int compress_type = btrfs_file_extent_compression(leaf, fi);

        em->bdev = root->fs_info->fs_devices->latest_bdev;
        btrfs_item_key_to_cpu(leaf, &key, slot);
        extent_start = key.offset;

        if (type == BTRFS_FILE_EXTENT_REG ||
            type == BTRFS_FILE_EXTENT_PREALLOC) {
                extent_end = extent_start +
                        btrfs_file_extent_num_bytes(leaf, fi);
        } else if (type == BTRFS_FILE_EXTENT_INLINE) {
                size_t size;
                size = btrfs_file_extent_inline_len(leaf, slot, fi);
                extent_end = ALIGN(extent_start + size, root->sectorsize);
        }

        em->ram_bytes = btrfs_file_extent_ram_bytes(leaf, fi);
        if (type == BTRFS_FILE_EXTENT_REG ||
            type == BTRFS_FILE_EXTENT_PREALLOC) {
                em->start = extent_start;
                em->len = extent_end - extent_start;
                em->orig_start = extent_start -
                        btrfs_file_extent_offset(leaf, fi);
                em->orig_block_len = btrfs_file_extent_disk_num_bytes(leaf, fi);
                bytenr = btrfs_file_extent_disk_bytenr(leaf, fi);
                if (bytenr == 0) {
                        em->block_start = EXTENT_MAP_HOLE;
                        return;
                }
                if (compress_type != BTRFS_COMPRESS_NONE) {
                        set_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                        em->compress_type = compress_type;
                        em->block_start = bytenr;
                        em->block_len = em->orig_block_len;
                } else {
                        bytenr += btrfs_file_extent_offset(leaf, fi);
                        em->block_start = bytenr;
                        em->block_len = em->len;
                        if (type == BTRFS_FILE_EXTENT_PREALLOC)
                                set_bit(EXTENT_FLAG_PREALLOC, &em->flags);
                }
        } else if (type == BTRFS_FILE_EXTENT_INLINE) {
                em->block_start = EXTENT_MAP_INLINE;
                em->start = extent_start;
                em->len = extent_end - extent_start;
                /*
                 * Initialize orig_start and block_len with the same values
                 * as in inode.c:btrfs_get_extent().
                 */
                em->orig_start = EXTENT_MAP_HOLE;
                em->block_len = (u64)-1;
                if (!new_inline && compress_type != BTRFS_COMPRESS_NONE) {
                        set_bit(EXTENT_FLAG_COMPRESSED, &em->flags);
                        em->compress_type = compress_type;
                }
        } else {
                btrfs_err(root->fs_info,
                          "unknown file extent item type %d, inode %llu, offset %llu, root %llu",
                          type, btrfs_ino(inode), extent_start,
                          root->root_key.objectid);
        }
}