rbd: Refactor bio cloning

					unsigned int len,

					gfp_t gfpmask)

{

	struct bio_vec bv;

	struct bvec_iter iter;

	struct bvec_iter end_iter;

	unsigned int resid;

	unsigned int voff;

	unsigned short vcnt;

	struct bio *bio;

	/* Handle the easy case for the caller */

	if (!offset && len == bio_src->bi_iter.bi_size)

		return bio_clone(bio_src, gfpmask);

	if (WARN_ON_ONCE(!len))

		return NULL;

	if (WARN_ON_ONCE(len > bio_src->bi_iter.bi_size))

		return NULL;

	if (WARN_ON_ONCE(offset > bio_src->bi_iter.bi_size - len))

		return NULL;

	/* Find first affected segment... */

	resid = offset;

	bio_for_each_segment(bv, bio_src, iter) {

		if (resid < bv.bv_len)

			break;

		resid -= bv.bv_len;

	}

	voff = resid;

	/* ...and the last affected segment */

	resid += len;

	__bio_for_each_segment(bv, bio_src, end_iter, iter) {

		if (resid <= bv.bv_len)

			break;

		resid -= bv.bv_len;

	}

	vcnt = end_iter.bi_idx = iter.bi_idx + 1;

	/* Build the clone */

	bio = bio_alloc(gfpmask, (unsigned int) vcnt);

	bio = bio_clone(bio_src, gfpmask);

	if (!bio)

		return NULL;	/* ENOMEM */

	bio->bi_bdev = bio_src->bi_bdev;

	bio->bi_iter.bi_sector = bio_src->bi_iter.bi_sector +

		(offset >> SECTOR_SHIFT);

	bio->bi_rw = bio_src->bi_rw;

	bio->bi_flags |= 1 << BIO_CLONED;

	/*

	 * Copy over our part of the bio_vec, then update the first

	 * and last (or only) entries.

	 */

	memcpy(&bio->bi_io_vec[0], &bio_src->bi_io_vec[iter.bi_idx],

			vcnt * sizeof (struct bio_vec));

	bio->bi_io_vec[0].bv_offset += voff;

	if (vcnt > 1) {

		bio->bi_io_vec[0].bv_len -= voff;

		bio->bi_io_vec[vcnt - 1].bv_len = resid;

	} else {

		bio->bi_io_vec[0].bv_len = len;

	}

	bio->bi_vcnt = vcnt;

	bio_advance(bio, offset);

	bio->bi_iter.bi_size = len;

	return bio;