Re: [dm-devel] [PATCH 4/9] block: Make generic_make_request handle arbitrary sized bios

Mike Christie
2013-11-05T00:05:32Z

On 11/04/2013 03:36 PM, Kent Overstreet wrote:
> @@ -1822,6 +1820,14 @@ void generic_make_request(struct bio *bio)
> */
> blk_queue_bounce(q, &bio);
>
> + if (!blk_queue_largebios(q))
> + split = blk_bio_segment_split(q, bio, q->bio_split);

Is it assumed bios coming down this path are created using bio_add_page?
If not, does blk_bio_segment_split need a queue_max_sectors or
queue_max_hw_sectors check? I only saw a segment count check below.

> +
> +struct bio *blk_bio_segment_split(struct request_queue *q, struct bio *bio,
> + struct bio_set *bs)
> +{
> + struct bio *split;
> + struct bio_vec bv, bvprv;
> + struct bvec_iter iter;
> + unsigned seg_size = 0, nsegs = 0;
> + int prev = 0;
> +
> + struct bvec_merge_data bvm = {
> + .bi_bdev = bio->bi_bdev,
> + .bi_sector = bio->bi_iter.bi_sector,
> + .bi_size = 0,
> + .bi_rw = bio->bi_rw,
> + };
> +
> + if (bio->bi_rw & REQ_DISCARD)
> + return blk_bio_discard_split(q, bio, bs);
> +
> + if (bio->bi_rw & REQ_WRITE_SAME)
> + return blk_bio_write_same_split(q, bio, bs);
> +
> + bio_for_each_segment(bv, bio, iter) {
> + if (q->merge_bvec_fn &&
> + q->merge_bvec_fn(q, &bvm, &bv) < (int) bv.bv_len)
> + goto split;
> +
> + bvm.bi_size += bv.bv_len;
> +
> + if (prev && blk_queue_cluster(q)) {
> + if (seg_size + bv.bv_len > queue_max_segment_size(q))
> + goto new_segment;
> + if (!BIOVEC_PHYS_MERGEABLE(&bvprv, &bv))
> + goto new_segment;
> + if (!BIOVEC_SEG_BOUNDARY(q, &bvprv, &bv))
> + goto new_segment;
> +
> + seg_size += bv.bv_len;
> + bvprv = bv;
> + prev = 1;
> + continue;
> + }
> +new_segment:
> + if (nsegs == queue_max_segments(q))
> + goto split;
> +
> + nsegs++;
> + bvprv = bv;
> + prev = 1;
> + seg_size = bv.bv_len;
> + }
> +
> + return NULL;
> +split:
> + split = bio_clone_bioset(bio, GFP_NOIO, bs);
> +
> + split->bi_iter.bi_size -= iter.bi_size;
> + bio->bi_iter = iter;
> +
> + if (bio_integrity(bio)) {
> + bio_integrity_advance(bio, split->bi_iter.bi_size);
> + bio_integrity_trim(split, 0, bio_sectors(split));
> + }
> +
> + return split;
> +}