extern int bio_get_nr_vecs(struct block_device *);
struct rq_map_data;
extern struct bio *bio_map_user_iov(struct request_queue *,
- struct block_device *,
const struct iov_iter *, gfp_t);
extern void bio_unmap_user(struct bio *);
extern struct bio *bio_map_kern(struct request_queue *, void *, unsigned int,