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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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fs/bio.c
+70 -6
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@@ -273,6 +273,7 @@ void bio_init(struct bio *bio)
{
memset(bio, 0, sizeof(*bio));
bio->bi_flags = 1 << BIO_UPTODATE;
atomic_set(&bio->bi_remaining, 1);
atomic_set(&bio->bi_cnt, 1);
}
EXPORT_SYMBOL(bio_init);
@@ -295,9 +296,35 @@ void bio_reset(struct bio *bio)
memset(bio, 0, BIO_RESET_BYTES);
bio->bi_flags = flags|(1 << BIO_UPTODATE);
atomic_set(&bio->bi_remaining, 1);
}
EXPORT_SYMBOL(bio_reset);
static void bio_chain_endio(struct bio *bio, int error)
{
bio_endio(bio->bi_private, error);
bio_put(bio);
}
/**
* bio_chain - chain bio completions
*
* The caller won't have a bi_end_io called when @bio completes - instead,
* @parent's bi_end_io won't be called until both @parent and @bio have
* completed; the chained bio will also be freed when it completes.
*
* The caller must not set bi_private or bi_end_io in @bio.
*/
void bio_chain(struct bio *bio, struct bio *parent)
{
BUG_ON(bio->bi_private || bio->bi_end_io);
bio->bi_private = parent;
bio->bi_end_io = bio_chain_endio;
atomic_inc(&parent->bi_remaining);
}
EXPORT_SYMBOL(bio_chain);
static void bio_alloc_rescue(struct work_struct *work)
{
struct bio_set *bs = container_of(work, struct bio_set, rescue_work);
@@ -1719,16 +1746,53 @@ EXPORT_SYMBOL(bio_flush_dcache_pages);
**/
void bio_endio(struct bio *bio, int error)
{
if (error)
clear_bit(BIO_UPTODATE, &bio->bi_flags);
else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
error = -EIO;
while (bio) {
BUG_ON(atomic_read(&bio->bi_remaining) <= 0);
if (bio->bi_end_io)
bio->bi_end_io(bio, error);
if (error)
clear_bit(BIO_UPTODATE, &bio->bi_flags);
else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
error = -EIO;
if (!atomic_dec_and_test(&bio->bi_remaining))
return;
/*
* Need to have a real endio function for chained bios,
* otherwise various corner cases will break (like stacking
* block devices that save/restore bi_end_io) - however, we want
* to avoid unbounded recursion and blowing the stack. Tail call
* optimization would handle this, but compiling with frame
* pointers also disables gcc's sibling call optimization.
*/
if (bio->bi_end_io == bio_chain_endio) {
struct bio *parent = bio->bi_private;
bio_put(bio);
bio = parent;
} else {
if (bio->bi_end_io)
bio->bi_end_io(bio, error);
bio = NULL;
}
}
}
EXPORT_SYMBOL(bio_endio);
/**
* bio_endio_nodec - end I/O on a bio, without decrementing bi_remaining
* @bio: bio
* @error: error, if any
*
* For code that has saved and restored bi_end_io; thing hard before using this
* function, probably you should've cloned the entire bio.
**/
void bio_endio_nodec(struct bio *bio, int error)
{
atomic_inc(&bio->bi_remaining);
bio_endio(bio, error);
}
EXPORT_SYMBOL(bio_endio_nodec);
void bio_pair_release(struct bio_pair *bp)
{
if (atomic_dec_and_test(&bp->cnt)) {