/*
 * 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);