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dm: refactor bio cloning

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

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
This commit is contained in:
Alasdair G Kergon 2013-03-01 22:45:47 +00:00
parent 14fe594d67
commit e4c938111f
1 changed files with 96 additions and 68 deletions
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164
drivers/md/dm.c
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@ -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);
@ -1238,12 +1244,69 @@ static int __send_write_same(struct clone_info *ci)
return __send_changing_extent_only(ci, get_num_write_same_bios, NULL);
}
/*
* Find maximum number of sectors / bvecs we can process with a single bio.
*/
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 (*idx = ci->idx; max && (*idx < bio->bi_vcnt); (*idx)++) {
bv_len = to_sector(bio->bi_io_vec[*idx].bv_len);
if (bv_len > max)
break;
max -= bv_len;
total_len += bv_len;
}
return total_len;
}
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 offset = 0;
sector_t len;
do {
if (offset) {
ti = dm_table_find_target(ci->map, ci->sector);
if (!dm_target_is_valid(ti))
return -EIO;
max = max_io_len(ci->sector, ti);
}
len = min(remaining, max);
__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;
offset += to_bytes(len);
} 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 = 0, max;
struct dm_target_io *tio;
sector_t len, max;
int idx;
if (unlikely(bio->bi_rw & REQ_DISCARD))
return __send_discard(ci);
@ -1256,74 +1319,39 @@ static int __split_and_process_non_flush(struct clone_info *ci)
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) {
/*
* 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);
__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;
}
} 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.
*/
int i;
sector_t remaining = max;
sector_t bv_len;
/*
* 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);
for (i = ci->idx; remaining && (i < bio->bi_vcnt); i++) {
bv_len = to_sector(bio->bi_io_vec[i].bv_len);
if (bv_len > remaining)
break;
remaining -= bv_len;
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);
__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 = i;
ci->idx = idx;
} else {
/*
* Handle a bvec that must be split between two or more targets.
*/
struct bio_vec *bv = bio->bi_io_vec + ci->idx;
sector_t remaining = to_sector(bv->bv_len);
unsigned int offset = 0;
do {
if (offset) {
ti = dm_table_find_target(ci->map, ci->sector);
if (!dm_target_is_valid(ti))
return -EIO;
max = max_io_len(ci->sector, ti);
}
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);
ci->sector += len;
ci->sector_count -= len;
offset += to_bytes(len);
} while (remaining -= len);
ci->idx++;
return 0;
}
return 0;
/*
* Handle a bvec that must be split between two or more targets.
*/
return __split_bvec_across_targets(ci, ti, max);
}
/*