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Commit e4c93811 authored by Alasdair G Kergon's avatar Alasdair G Kergon
Browse files

dm: refactor bio cloning 



Refactor part of the bio splitting and cloning code to try to make it
easier to understand.

Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 14fe594d

drivers/md/dm.c

+96 −68
Original line number Diff line number Diff line
@@ -1087,7 +1087,7 @@ static void clone_split_bio(struct dm_target_io *tio, struct bio *bio, 
 */

static void clone_bio(struct dm_target_io *tio, struct bio *bio,

		      sector_t sector, unsigned short idx,

		      unsigned short bv_count, unsigned int len)

		      unsigned short bv_count, unsigned len)

{

	struct bio *clone = &tio->clone;

	unsigned trim = 0;
@@ -1159,17 +1159,23 @@ static int __send_empty_flush(struct clone_info *ci) 
	return 0;

}



static void __clone_and_map_data_bio(struct clone_info *ci,

				     struct dm_target *ti)

static void __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,

				     sector_t sector, int nr_iovecs,

				     unsigned short idx, unsigned short bv_count,

				     unsigned offset, unsigned len,

				     unsigned split_bvec)

{

	struct bio *bio = ci->bio;

	struct dm_target_io *tio;



	tio = alloc_tio(ci, ti, bio->bi_max_vecs, 0);

	clone_bio(tio, bio, ci->sector, ci->idx, bio->bi_vcnt - ci->idx,

		  ci->sector_count);

	tio = alloc_tio(ci, ti, nr_iovecs, 0);



	if (split_bvec)

		clone_split_bio(tio, bio, sector, idx, offset, len);

	else

		clone_bio(tio, bio, sector, idx, bv_count, len);



	__map_bio(tio);

	ci->sector_count = 0;

}



typedef unsigned (*get_num_bios_fn)(struct dm_target *ti);
@@ -1238,65 +1244,35 @@ static int __send_write_same(struct clone_info *ci) 
	return __send_changing_extent_only(ci, get_num_write_same_bios, NULL);

}



static int __split_and_process_non_flush(struct clone_info *ci)

{

	struct bio *bio = ci->bio;

	struct dm_target *ti;

	sector_t len = 0, max;

	struct dm_target_io *tio;



	if (unlikely(bio->bi_rw & REQ_DISCARD))

		return __send_discard(ci);

	else if (unlikely(bio->bi_rw & REQ_WRITE_SAME))

		return __send_write_same(ci);



	ti = dm_table_find_target(ci->map, ci->sector);

	if (!dm_target_is_valid(ti))

		return -EIO;



	max = max_io_len(ci->sector, ti);



	if (ci->sector_count <= max) {

		/*

		 * Optimise for the simple case where we can do all of

		 * the remaining io with a single clone.

		 */

		__clone_and_map_data_bio(ci, ti);



	} else if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {

/*

		 * There are some bvecs that don't span targets.

		 * Do as many of these as possible.

 * Find maximum number of sectors / bvecs we can process with a single bio.

 */

		int i;

		sector_t remaining = max;

		sector_t bv_len;

static sector_t __len_within_target(struct clone_info *ci, sector_t max, int *idx)

{

	struct bio *bio = ci->bio;

	sector_t bv_len, total_len = 0;



		for (i = ci->idx; remaining && (i < bio->bi_vcnt); i++) {

			bv_len = to_sector(bio->bi_io_vec[i].bv_len);

	for (*idx = ci->idx; max && (*idx < bio->bi_vcnt); (*idx)++) {

		bv_len = to_sector(bio->bi_io_vec[*idx].bv_len);



			if (bv_len > remaining)

		if (bv_len > max)

			break;



			remaining -= bv_len;

			len += bv_len;

		max -= bv_len;

		total_len += bv_len;

	}



		tio = alloc_tio(ci, ti, bio->bi_max_vecs, 0);

		clone_bio(tio, bio, ci->sector, ci->idx, i - ci->idx, len);

		__map_bio(tio);



		ci->sector += len;

		ci->sector_count -= len;

		ci->idx = i;

	return total_len;

}



	} else {

		/*

		 * Handle a bvec that must be split between two or more targets.

		 */

static int __split_bvec_across_targets(struct clone_info *ci,

				       struct dm_target *ti, sector_t max)

{

	struct bio *bio = ci->bio;

	struct bio_vec *bv = bio->bi_io_vec + ci->idx;

	sector_t remaining = to_sector(bv->bv_len);

		unsigned int offset = 0;

	unsigned offset = 0;

	sector_t len;



	do {

		if (offset) {
@@ -1309,11 +1285,8 @@ static int __split_and_process_non_flush(struct clone_info *ci) 


		len = min(remaining, max);



			tio = alloc_tio(ci, ti, 1, 0);

			clone_split_bio(tio, bio, ci->sector, ci->idx,

					bv->bv_offset + offset, len);



			__map_bio(tio);

		__clone_and_map_data_bio(ci, ti, ci->sector, 1, ci->idx, 0,

					 bv->bv_offset + offset, len, 1);



		ci->sector += len;

		ci->sector_count -= len;
@@ -1321,11 +1294,66 @@ static int __split_and_process_non_flush(struct clone_info *ci) 
	} while (remaining -= len);



	ci->idx++;



	return 0;

}



/*

 * Select the correct strategy for processing a non-flush bio.

 */

static int __split_and_process_non_flush(struct clone_info *ci)

{

	struct bio *bio = ci->bio;

	struct dm_target *ti;

	sector_t len, max;

	int idx;



	if (unlikely(bio->bi_rw & REQ_DISCARD))

		return __send_discard(ci);

	else if (unlikely(bio->bi_rw & REQ_WRITE_SAME))

		return __send_write_same(ci);



	ti = dm_table_find_target(ci->map, ci->sector);

	if (!dm_target_is_valid(ti))

		return -EIO;



	max = max_io_len(ci->sector, ti);



	/*

	 * Optimise for the simple case where we can do all of

	 * the remaining io with a single clone.

	 */

	if (ci->sector_count <= max) {

		__clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,

					 ci->idx, bio->bi_vcnt - ci->idx, 0,

					 ci->sector_count, 0);

		ci->sector_count = 0;

		return 0;

	}



	/*

	 * There are some bvecs that don't span targets.

	 * Do as many of these as possible.

	 */

	if (to_sector(bio->bi_io_vec[ci->idx].bv_len) <= max) {

		len = __len_within_target(ci, max, &idx);



		__clone_and_map_data_bio(ci, ti, ci->sector, bio->bi_max_vecs,

					 ci->idx, idx - ci->idx, 0, len, 0);



		ci->sector += len;

		ci->sector_count -= len;

		ci->idx = idx;



		return 0;

	}



	/*

	 * Handle a bvec that must be split between two or more targets.

	 */

	return __split_bvec_across_targets(ci, ti, max);

}



/*

 * Entry point to split a bio into clones and submit them to the targets.

 */