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block: Generic bio chaining

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This adds a generic mechanism for chaining bio completions. This is
going to be used for a bio_split() replacement, and it turns out to be
very useful in a fair amount of driver code - a fair number of drivers
were implementing this in their own roundabout ways, often painfully.

Note that this means it's no longer to call bio_endio() more than once
on the same bio! This can cause problems for drivers that save/restore
bi_end_io. Arguably they shouldn't be saving/restoring bi_end_io at all
- in all but the simplest cases they'd be better off just cloning the
bio, and immutable biovecs is making bio cloning cheaper. But for now,
we add a bio_endio_nodec() for these cases.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Kent Overstreet
2013-11-23 18:34:15 -08:00
parent e90abc8ec3
commit 196d38bccf
9 changed files with 90 additions and 11 deletions
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8
drivers/md/dm-thin.c
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@@ -611,8 +611,10 @@ static void cell_defer_no_holder(struct thin_c *tc, struct dm_bio_prison_cell *c
static void process_prepared_mapping_fail(struct dm_thin_new_mapping *m)
{
if (m->bio)
if (m->bio) {
m->bio->bi_end_io = m->saved_bi_end_io;
atomic_inc(&m->bio->bi_remaining);
}
cell_error(m->tc->pool, m->cell);
list_del(&m->list);
mempool_free(m, m->tc->pool->mapping_pool);
@@ -626,8 +628,10 @@ static void process_prepared_mapping(struct dm_thin_new_mapping *m)
int r;
bio = m->bio;
if (bio)
if (bio) {
bio->bi_end_io = m->saved_bi_end_io;
atomic_inc(&bio->bi_remaining);
}
if (m->err) {
cell_error(pool, m->cell);