+/*
+ * Find checksums for logical bytenr range [disk_bytenr, disk_bytenr + len) and
+ * estore the result to @dst.
+ *
+ * Return >0 for the number of sectors we found.
+ * Return 0 for the range [disk_bytenr, disk_bytenr + sectorsize) has no csum
+ * for it. Caller may want to try next sector until one range is hit.
+ * Return <0 for fatal error.
+ */
+static int search_csum_tree(struct btrfs_fs_info *fs_info,
+ struct btrfs_path *path, u64 disk_bytenr,
+ u64 len, u8 *dst)
+{
+ struct btrfs_csum_item *item = NULL;
+ struct btrfs_key key;
+ const u32 sectorsize = fs_info->sectorsize;
+ const u32 csum_size = fs_info->csum_size;
+ u32 itemsize;
+ int ret;
+ u64 csum_start;
+ u64 csum_len;
+
+ ASSERT(IS_ALIGNED(disk_bytenr, sectorsize) &&
+ IS_ALIGNED(len, sectorsize));
+
+ /* Check if the current csum item covers disk_bytenr */
+ if (path->nodes[0]) {
+ item = btrfs_item_ptr(path->nodes[0], path->slots[0],
+ struct btrfs_csum_item);
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+ itemsize = btrfs_item_size_nr(path->nodes[0], path->slots[0]);
+
+ csum_start = key.offset;
+ csum_len = (itemsize / csum_size) * sectorsize;
+
+ if (in_range(disk_bytenr, csum_start, csum_len))
+ goto found;
+ }
+
+ /* Current item doesn't contain the desired range, search again */
+ btrfs_release_path(path);
+ item = btrfs_lookup_csum(NULL, fs_info->csum_root, path, disk_bytenr, 0);
+ if (IS_ERR(item)) {
+ ret = PTR_ERR(item);
+ goto out;
+ }
+ btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
+ itemsize = btrfs_item_size_nr(path->nodes[0], path->slots[0]);
+
+ csum_start = key.offset;
+ csum_len = (itemsize / csum_size) * sectorsize;
+ ASSERT(in_range(disk_bytenr, csum_start, csum_len));
+
+found:
+ ret = (min(csum_start + csum_len, disk_bytenr + len) -
+ disk_bytenr) >> fs_info->sectorsize_bits;
+ read_extent_buffer(path->nodes[0], dst, (unsigned long)item,
+ ret * csum_size);
+out:
+ if (ret == -ENOENT)
+ ret = 0;
+ return ret;
+}
+
+/*
+ * Locate the file_offset of @cur_disk_bytenr of a @bio.
+ *
+ * Bio of btrfs represents read range of
+ * [bi_sector << 9, bi_sector << 9 + bi_size).
+ * Knowing this, we can iterate through each bvec to locate the page belong to
+ * @cur_disk_bytenr and get the file offset.
+ *
+ * @inode is used to determine if the bvec page really belongs to @inode.
+ *
+ * Return 0 if we can't find the file offset
+ * Return >0 if we find the file offset and restore it to @file_offset_ret
+ */
+static int search_file_offset_in_bio(struct bio *bio, struct inode *inode,
+ u64 disk_bytenr, u64 *file_offset_ret)
+{
+ struct bvec_iter iter;
+ struct bio_vec bvec;
+ u64 cur = bio->bi_iter.bi_sector << SECTOR_SHIFT;
+ int ret = 0;
+
+ bio_for_each_segment(bvec, bio, iter) {
+ struct page *page = bvec.bv_page;
+
+ if (cur > disk_bytenr)
+ break;
+ if (cur + bvec.bv_len <= disk_bytenr) {
+ cur += bvec.bv_len;
+ continue;
+ }
+ ASSERT(in_range(disk_bytenr, cur, bvec.bv_len));
+ if (page->mapping && page->mapping->host &&
+ page->mapping->host == inode) {
+ ret = 1;
+ *file_offset_ret = page_offset(page) + bvec.bv_offset +
+ disk_bytenr - cur;
+ break;
+ }
+ }
+ return ret;
+}
+