- btrfs_item_key_to_cpu(leaf, &key, slot);
- if (isize <= key.offset)
- return 0;
- new_item_span = isize - key.offset;
- blocks = (new_item_span + root->sectorsize - 1) / root->sectorsize;
- new_item_size = blocks * BTRFS_CRC32_SIZE;
- if (new_item_size >= btrfs_item_size_nr(leaf, slot))
- return 0;
- ret = btrfs_truncate_item(trans, root, path, new_item_size, 1);
- BUG_ON(ret);
- return ret;
+ 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;
+
+ ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
+ if (ret > 0) {
+ if (path->slots[0] == 0)
+ goto out;
+ path->slots[0]--;
+ }
+ 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;
+ csum_end += key.offset;
+
+ /* this csum ends before we start, we're done */
+ if (csum_end <= bytenr)
+ break;
+
+ /* delete the entire item, it is inside our range */
+ if (key.offset >= bytenr && csum_end <= end_byte) {
+ ret = btrfs_del_item(trans, root, path);
+ BUG_ON(ret);
+ } 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;
+ offset *= csum_size;
+
+ shift_len = (len / blocksize) * 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(root, path, &key, bytenr, len);
+ BUG_ON(ret);
+ }
+ btrfs_release_path(path);
+ }
+out:
+ btrfs_free_path(path);
+ return 0;