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linux/block/blk-barrier.c
David Woodhouse e17fc0a1cc Allow elevators to sort/merge discard requests 
But blkdev_issue_discard() still emits requests which are interpreted as
soft barriers, because naïve callers might otherwise issue subsequent
writes to those same sectors, which might cross on the queue (if they're
reallocated quickly enough).

Callers still _can_ issue non-barrier discard requests, but they have to
take care of queue ordering for themselves.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09 08:56:02 +02:00

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/*
* Functions related to barrier IO handling
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include "blk.h"
/**
* blk_queue_ordered - does this queue support ordered writes
* @q: the request queue
* @ordered: one of QUEUE_ORDERED_*
* @prepare_flush_fn: rq setup helper for cache flush ordered writes
*
* Description:
* For journalled file systems, doing ordered writes on a commit
* block instead of explicitly doing wait_on_buffer (which is bad
* for performance) can be a big win. Block drivers supporting this
* feature should call this function and indicate so.
*
**/
int blk_queue_ordered(struct request_queue *q, unsigned ordered,
prepare_flush_fn *prepare_flush_fn)
{
if (ordered & (QUEUE_ORDERED_PREFLUSH | QUEUE_ORDERED_POSTFLUSH) &&
prepare_flush_fn == NULL) {
printk(KERN_ERR "%s: prepare_flush_fn required\n", __func__);
return -EINVAL;
}
if (ordered != QUEUE_ORDERED_NONE &&
ordered != QUEUE_ORDERED_DRAIN &&
ordered != QUEUE_ORDERED_DRAIN_FLUSH &&
ordered != QUEUE_ORDERED_DRAIN_FUA &&
ordered != QUEUE_ORDERED_TAG &&
ordered != QUEUE_ORDERED_TAG_FLUSH &&
ordered != QUEUE_ORDERED_TAG_FUA) {
printk(KERN_ERR "blk_queue_ordered: bad value %d\n", ordered);
return -EINVAL;
}
q->ordered = ordered;
q->next_ordered = ordered;
q->prepare_flush_fn = prepare_flush_fn;
return 0;
}
EXPORT_SYMBOL(blk_queue_ordered);
/*
* Cache flushing for ordered writes handling
*/
unsigned blk_ordered_cur_seq(struct request_queue *q)
{
if (!q->ordseq)
return 0;
return 1 << ffz(q->ordseq);
}
unsigned blk_ordered_req_seq(struct request *rq)
{
struct request_queue *q = rq->q;
BUG_ON(q->ordseq == 0);
if (rq == &q->pre_flush_rq)
return QUEUE_ORDSEQ_PREFLUSH;
if (rq == &q->bar_rq)
return QUEUE_ORDSEQ_BAR;
if (rq == &q->post_flush_rq)
return QUEUE_ORDSEQ_POSTFLUSH;
/*
* !fs requests don't need to follow barrier ordering. Always
* put them at the front. This fixes the following deadlock.
*
* http://thread.gmane.org/gmane.linux.kernel/537473
*/
if (!blk_fs_request(rq))
return QUEUE_ORDSEQ_DRAIN;
if ((rq->cmd_flags & REQ_ORDERED_COLOR) ==
(q->orig_bar_rq->cmd_flags & REQ_ORDERED_COLOR))
return QUEUE_ORDSEQ_DRAIN;
else
return QUEUE_ORDSEQ_DONE;
}
void blk_ordered_complete_seq(struct request_queue *q, unsigned seq, int error)
{
struct request *rq;
if (error && !q->orderr)
q->orderr = error;
BUG_ON(q->ordseq & seq);
q->ordseq |= seq;
if (blk_ordered_cur_seq(q) != QUEUE_ORDSEQ_DONE)
return;
/*
* Okay, sequence complete.
*/
q->ordseq = 0;
rq = q->orig_bar_rq;
if (__blk_end_request(rq, q->orderr, blk_rq_bytes(rq)))
BUG();
}
static void pre_flush_end_io(struct request *rq, int error)
{
elv_completed_request(rq->q, rq);
blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_PREFLUSH, error);
}
static void bar_end_io(struct request *rq, int error)
{
elv_completed_request(rq->q, rq);
blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_BAR, error);
}
static void post_flush_end_io(struct request *rq, int error)
{
elv_completed_request(rq->q, rq);
blk_ordered_complete_seq(rq->q, QUEUE_ORDSEQ_POSTFLUSH, error);
}
static void queue_flush(struct request_queue *q, unsigned which)
{
struct request *rq;
rq_end_io_fn *end_io;
if (which == QUEUE_ORDERED_PREFLUSH) {
rq = &q->pre_flush_rq;
end_io = pre_flush_end_io;
} else {
rq = &q->post_flush_rq;
end_io = post_flush_end_io;
}
blk_rq_init(q, rq);
rq->cmd_flags = REQ_HARDBARRIER;
rq->rq_disk = q->bar_rq.rq_disk;
rq->end_io = end_io;
q->prepare_flush_fn(q, rq);
elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
}
static inline struct request *start_ordered(struct request_queue *q,
struct request *rq)
{
q->orderr = 0;
q->ordered = q->next_ordered;
q->ordseq |= QUEUE_ORDSEQ_STARTED;
/*
* Prep proxy barrier request.
*/
blkdev_dequeue_request(rq);
q->orig_bar_rq = rq;
rq = &q->bar_rq;
blk_rq_init(q, rq);
if (bio_data_dir(q->orig_bar_rq->bio) == WRITE)
rq->cmd_flags |= REQ_RW;
if (q->ordered & QUEUE_ORDERED_FUA)
rq->cmd_flags |= REQ_FUA;
init_request_from_bio(rq, q->orig_bar_rq->bio);
rq->end_io = bar_end_io;
/*
* Queue ordered sequence. As we stack them at the head, we
* need to queue in reverse order. Note that we rely on that
* no fs request uses ELEVATOR_INSERT_FRONT and thus no fs
* request gets inbetween ordered sequence. If this request is
* an empty barrier, we don't need to do a postflush ever since
* there will be no data written between the pre and post flush.
* Hence a single flush will suffice.
*/
if ((q->ordered & QUEUE_ORDERED_POSTFLUSH) && !blk_empty_barrier(rq))
queue_flush(q, QUEUE_ORDERED_POSTFLUSH);
else
q->ordseq |= QUEUE_ORDSEQ_POSTFLUSH;
elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
if (q->ordered & QUEUE_ORDERED_PREFLUSH) {
queue_flush(q, QUEUE_ORDERED_PREFLUSH);
rq = &q->pre_flush_rq;
} else
q->ordseq |= QUEUE_ORDSEQ_PREFLUSH;
if ((q->ordered & QUEUE_ORDERED_TAG) || q->in_flight == 0)
q->ordseq |= QUEUE_ORDSEQ_DRAIN;
else
rq = NULL;
return rq;
}
int blk_do_ordered(struct request_queue *q, struct request **rqp)
{
struct request *rq = *rqp;
const int is_barrier = blk_fs_request(rq) && blk_barrier_rq(rq);
if (!q->ordseq) {
if (!is_barrier)
return 1;
if (q->next_ordered != QUEUE_ORDERED_NONE) {
*rqp = start_ordered(q, rq);
return 1;
} else {
/*
* This can happen when the queue switches to
* ORDERED_NONE while this request is on it.
*/
blkdev_dequeue_request(rq);
if (__blk_end_request(rq, -EOPNOTSUPP,
blk_rq_bytes(rq)))
BUG();
*rqp = NULL;
return 0;
}
}
/*
* Ordered sequence in progress
*/
/* Special requests are not subject to ordering rules. */
if (!blk_fs_request(rq) &&
rq != &q->pre_flush_rq && rq != &q->post_flush_rq)
return 1;
if (q->ordered & QUEUE_ORDERED_TAG) {
/* Ordered by tag. Blocking the next barrier is enough. */
if (is_barrier && rq != &q->bar_rq)
*rqp = NULL;
} else {
/* Ordered by draining. Wait for turn. */
WARN_ON(blk_ordered_req_seq(rq) < blk_ordered_cur_seq(q));
if (blk_ordered_req_seq(rq) > blk_ordered_cur_seq(q))
*rqp = NULL;
}
return 1;
}
static void bio_end_empty_barrier(struct bio *bio, int err)
{
if (err) {
if (err == -EOPNOTSUPP)
set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
clear_bit(BIO_UPTODATE, &bio->bi_flags);
}
complete(bio->bi_private);
}
/**
* blkdev_issue_flush - queue a flush
* @bdev: blockdev to issue flush for
* @error_sector: error sector
*
* Description:
* Issue a flush for the block device in question. Caller can supply
* room for storing the error offset in case of a flush error, if they
* wish to. Caller must run wait_for_completion() on its own.
*/
int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector)
{
DECLARE_COMPLETION_ONSTACK(wait);
struct request_queue *q;
struct bio *bio;
int ret;
if (bdev->bd_disk == NULL)
return -ENXIO;
q = bdev_get_queue(bdev);
if (!q)
return -ENXIO;
bio = bio_alloc(GFP_KERNEL, 0);
if (!bio)
return -ENOMEM;
bio->bi_end_io = bio_end_empty_barrier;
bio->bi_private = &wait;
bio->bi_bdev = bdev;
submit_bio(WRITE_BARRIER, bio);
wait_for_completion(&wait);
/*
* The driver must store the error location in ->bi_sector, if
* it supports it. For non-stacked drivers, this should be copied
* from rq->sector.
*/
if (error_sector)
*error_sector = bio->bi_sector;
ret = 0;
if (bio_flagged(bio, BIO_EOPNOTSUPP))
ret = -EOPNOTSUPP;
else if (!bio_flagged(bio, BIO_UPTODATE))
ret = -EIO;
bio_put(bio);
return ret;
}
EXPORT_SYMBOL(blkdev_issue_flush);
static void blkdev_discard_end_io(struct bio *bio, int err)
{
if (err) {
if (err == -EOPNOTSUPP)
set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
clear_bit(BIO_UPTODATE, &bio->bi_flags);
}
bio_put(bio);
}
/**
* blkdev_issue_discard - queue a discard
* @bdev: blockdev to issue discard for
* @sector: start sector
* @nr_sects: number of sectors to discard
*
* Description:
* Issue a discard request for the sectors in question. Does not wait.
*/
int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
unsigned nr_sects)
{
struct request_queue *q;
struct bio *bio;
int ret = 0;
if (bdev->bd_disk == NULL)
return -ENXIO;
q = bdev_get_queue(bdev);
if (!q)
return -ENXIO;
if (!q->prepare_discard_fn)
return -EOPNOTSUPP;
while (nr_sects && !ret) {
bio = bio_alloc(GFP_KERNEL, 0);
if (!bio)
return -ENOMEM;
bio->bi_end_io = blkdev_discard_end_io;
bio->bi_bdev = bdev;
bio->bi_sector = sector;
if (nr_sects > q->max_hw_sectors) {
bio->bi_size = q->max_hw_sectors << 9;
nr_sects -= q->max_hw_sectors;
sector += q->max_hw_sectors;
} else {
bio->bi_size = nr_sects << 9;
nr_sects = 0;
}
bio_get(bio);
submit_bio(DISCARD_BARRIER, bio);
/* Check if it failed immediately */
if (bio_flagged(bio, BIO_EOPNOTSUPP))
ret = -EOPNOTSUPP;
else if (!bio_flagged(bio, BIO_UPTODATE))
ret = -EIO;
bio_put(bio);
}
return ret;
}
EXPORT_SYMBOL(blkdev_issue_discard);
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