/*
   * 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);

  	/*
  	 * 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(root, 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
  ",
  					       (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, 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, 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;
  	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);
  			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);

  	} 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);

  
  		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)

  				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);
  			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(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;

  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;

  		ret = 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:

  	btrfs_free_path(path);

  	return ret;

  
  fail_unlock:

  	goto out;

  }