diff --git a/include/block/block_int.h b/include/block/block_int.h
index a48731d..1666066 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -156,8 +156,11 @@
 
     const char *protocol_name;
     int (*bdrv_truncate)(BlockDriverState *bs, int64_t offset);
+
     int64_t (*bdrv_getlength)(BlockDriverState *bs);
+    bool has_variable_length;
     int64_t (*bdrv_get_allocated_file_size)(BlockDriverState *bs);
+
     int (*bdrv_write_compressed)(BlockDriverState *bs, int64_t sector_num,
                                  const uint8_t *buf, int nb_sectors);