static void do_region(const blk_opf_t opf, unsigned int region,
		      struct dm_io_region *where, struct dpages *dp,
		      struct io *io)
static void do_region(const blk_opf_t opf, unsigned int region,
		      struct dm_io_region *where, struct dpages *dp,
		      struct io *io, unsigned short ioprio)