block: loop: pass multi-page bvec to iov_iter

		     loff_t pos, bool rw)

{

	struct iov_iter iter;

	struct req_iterator rq_iter;

	struct bio_vec *bvec;

	struct request *rq = blk_mq_rq_from_pdu(cmd);

	struct bio *bio = rq->bio;

	struct file *file = lo->lo_backing_file;

	struct bio_vec tmp;

	unsigned int offset;

	int segments = 0;

	int nr_bvec = 0;

	int ret;

	rq_for_each_bvec(tmp, rq, rq_iter)

		nr_bvec++;

	if (rq->bio != rq->biotail) {

		struct req_iterator iter;

		struct bio_vec tmp;

		__rq_for_each_bio(bio, rq)

			segments += bio_segments(bio);

		bvec = kmalloc_array(segments, sizeof(struct bio_vec),

		bvec = kmalloc_array(nr_bvec, sizeof(struct bio_vec),

				     GFP_NOIO);

		if (!bvec)

			return -EIO;

		/*

		 * The bios of the request may be started from the middle of

		 * the 'bvec' because of bio splitting, so we can't directly

		 * copy bio->bi_iov_vec to new bvec. The rq_for_each_segment

		 * copy bio->bi_iov_vec to new bvec. The rq_for_each_bvec

		 * API will take care of all details for us.

		 */

		rq_for_each_segment(tmp, rq, iter) {

		rq_for_each_bvec(tmp, rq, rq_iter) {

			*bvec = tmp;

			bvec++;

		}

		 */

		offset = bio->bi_iter.bi_bvec_done;

		bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);

		segments = bio_segments(bio);

	}

	atomic_set(&cmd->ref, 2);

	iov_iter_bvec(&iter, rw, bvec, segments, blk_rq_bytes(rq));

	iov_iter_bvec(&iter, rw, bvec, nr_bvec, blk_rq_bytes(rq));

	iter.iov_offset = offset;

	cmd->iocb.ki_pos = pos;