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/*
* Functions to sequence FLUSH and FUA writes.
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/gfp.h>

#include "blk.h"

/* FLUSH/FUA sequences */
enum {
QUEUE_FSEQ_STARTED = (1 << 0), /* flushing in progress */
QUEUE_FSEQ_PREFLUSH = (1 << 1), /* pre-flushing in progress */
QUEUE_FSEQ_DATA = (1 << 2), /* data write in progress */
QUEUE_FSEQ_POSTFLUSH = (1 << 3), /* post-flushing in progress */
QUEUE_FSEQ_DONE = (1 << 4),
};

static struct request *queue_next_fseq(struct request_queue *q);

unsigned blk_flush_cur_seq(struct request_queue *q)
{
if (!q->flush_seq)
return 0;
return 1 << ffz(q->flush_seq);
}

static struct request *blk_flush_complete_seq(struct request_queue *q,
unsigned seq, int error)
{
struct request *next_rq = NULL;

if (error && !q->flush_err)
q->flush_err = error;

BUG_ON(q->flush_seq & seq);
q->flush_seq |= seq;

if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
/* not complete yet, queue the next flush sequence */
next_rq = queue_next_fseq(q);
} else {
/* complete this flush request */
__blk_end_request_all(q->orig_flush_rq, q->flush_err);
q->orig_flush_rq = NULL;
q->flush_seq = 0;

/* dispatch the next flush if there's one */
if (!list_empty(&q->pending_flushes)) {
next_rq = list_entry_rq(q->pending_flushes.next);
list_move(&next_rq->queuelist, &q->queue_head);
}
}
return next_rq;
}

static void blk_flush_complete_seq_end_io(struct request_queue *q,
unsigned seq, int error)
{
bool was_empty = elv_queue_empty(q);
struct request *next_rq;

next_rq = blk_flush_complete_seq(q, seq, error);

/*
* Moving a request silently to empty queue_head may stall the
* queue. Kick the queue in those cases. This function is called
* from request completion path and calling directly into
* request_fn may confuse the driver. Always use kblockd.
*/
if (was_empty && next_rq)
__blk_run_queue(q, true);
}

static void pre_flush_end_io(struct request *rq, int error)
{
elv_completed_request(rq->q, rq);
blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
}

static void flush_data_end_io(struct request *rq, int error)
{
elv_completed_request(rq->q, rq);
blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
}

static void post_flush_end_io(struct request *rq, int error)
{
elv_completed_request(rq->q, rq);
blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
}

static void init_flush_request(struct request *rq, struct gendisk *disk)
{
rq->cmd_type = REQ_TYPE_FS;
rq->cmd_flags = WRITE_FLUSH;
rq->rq_disk = disk;
}

static struct request *queue_next_fseq(struct request_queue *q)
{
struct request *orig_rq = q->orig_flush_rq;
struct request *rq = &q->flush_rq;

blk_rq_init(q, rq);

switch (blk_flush_cur_seq(q)) {
case QUEUE_FSEQ_PREFLUSH:
init_flush_request(rq, orig_rq->rq_disk);
rq->end_io = pre_flush_end_io;
break;
case QUEUE_FSEQ_DATA:
init_request_from_bio(rq, orig_rq->bio);
/*
* orig_rq->rq_disk may be different from
* bio->bi_bdev->bd_disk if orig_rq got here through
* remapping drivers. Make sure rq->rq_disk points
* to the same one as orig_rq.
*/
rq->rq_disk = orig_rq->rq_disk;
rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
rq->end_io = flush_data_end_io;
break;
case QUEUE_FSEQ_POSTFLUSH:
init_flush_request(rq, orig_rq->rq_disk);
rq->end_io = post_flush_end_io;
break;
default:
BUG();
}

elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
return rq;
}

struct request *blk_do_flush(struct request_queue *q, struct request *rq)
{
unsigned int fflags = q->flush_flags; /* may change, cache it */
bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
unsigned skip = 0;

/*
* Special case. If there's data but flush is not necessary,
* the request can be issued directly.
*
* Flush w/o data should be able to be issued directly too but
* currently some drivers assume that rq->bio contains
* non-zero data if it isn't NULL and empty FLUSH requests
* getting here usually have bio's without data.
*/
if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
rq->cmd_flags &= ~REQ_FLUSH;
if (!has_fua)
rq->cmd_flags &= ~REQ_FUA;
return rq;
}

/*
* Sequenced flushes can't be processed in parallel. If
* another one is already in progress, queue for later
* processing.
*/
if (q->flush_seq) {
list_move_tail(&rq->queuelist, &q->pending_flushes);
return NULL;
}

/*
* Start a new flush sequence
*/
q->flush_err = 0;
q->flush_seq |= QUEUE_FSEQ_STARTED;

/* adjust FLUSH/FUA of the original request and stash it away */
rq->cmd_flags &= ~REQ_FLUSH;
if (!has_fua)
rq->cmd_flags &= ~REQ_FUA;
blk_dequeue_request(rq);
q->orig_flush_rq = rq;

/* skip unneded sequences and return the first one */
if (!do_preflush)
skip |= QUEUE_FSEQ_PREFLUSH;
if (!blk_rq_sectors(rq))
skip |= QUEUE_FSEQ_DATA;
if (!do_postflush)
skip |= QUEUE_FSEQ_POSTFLUSH;
return blk_flush_complete_seq(q, skip, 0);
}

static void bio_end_flush(struct bio *bio, int err)
{
if (err)
clear_bit(BIO_UPTODATE, &bio->bi_flags);
if (bio->bi_private)
complete(bio->bi_private);
bio_put(bio);
}

/**
* blkdev_issue_flush - queue a flush
* @bdev: blockdev to issue flush for
* @gfp_mask: memory allocation flags (for bio_alloc)
* @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. If WAIT flag is not passed then caller may check only what
* request was pushed in some internal queue for later handling.
*/
int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
sector_t *error_sector)
{
DECLARE_COMPLETION_ONSTACK(wait);
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;

/*
* some block devices may not have their queue correctly set up here
* (e.g. loop device without a backing file) and so issuing a flush
* here will panic. Ensure there is a request function before issuing
* the flush.
*/
if (!q->make_request_fn)
return -ENXIO;

bio = bio_alloc(gfp_mask, 0);
bio->bi_end_io = bio_end_flush;
bio->bi_bdev = bdev;
bio->bi_private = &wait;

bio_get(bio);
submit_bio(WRITE_FLUSH, 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 blk_rq_pos(rq).
*/
if (error_sector)
               *error_sector = bio->bi_sector;

if (!bio_flagged(bio, BIO_UPTODATE))
ret = -EIO;

bio_put(bio);
return ret;
}
EXPORT_SYMBOL(blkdev_issue_flush);
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