[linux-block.git] / block / blk-merge.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Functions related to segment and merge handling
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/blk-integrity.h>
#include <linux/scatterlist.h>
#include <linux/part_stat.h>
#include <linux/blk-cgroup.h>

#include <trace/events/block.h>

#include "blk.h"
#include "blk-mq-sched.h"
#include "blk-rq-qos.h"
#include "blk-throttle.h"

static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
{
        *bv = mp_bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
}

static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
{
        struct bvec_iter iter = bio->bi_iter;
        int idx;

        bio_get_first_bvec(bio, bv);
        if (bv->bv_len == bio->bi_iter.bi_size)
                return;         /* this bio only has a single bvec */

        bio_advance_iter(bio, &iter, iter.bi_size);

        if (!iter.bi_bvec_done)
                idx = iter.bi_idx - 1;
        else    /* in the middle of bvec */
                idx = iter.bi_idx;

        *bv = bio->bi_io_vec[idx];

        /*
         * iter.bi_bvec_done records actual length of the last bvec
         * if this bio ends in the middle of one io vector
         */
        if (iter.bi_bvec_done)
                bv->bv_len = iter.bi_bvec_done;
}

static inline bool bio_will_gap(struct request_queue *q,
                struct request *prev_rq, struct bio *prev, struct bio *next)
{
        struct bio_vec pb, nb;

        if (!bio_has_data(prev) || !queue_virt_boundary(q))
                return false;

        /*
         * Don't merge if the 1st bio starts with non-zero offset, otherwise it
         * is quite difficult to respect the sg gap limit.  We work hard to
         * merge a huge number of small single bios in case of mkfs.
         */
        if (prev_rq)
                bio_get_first_bvec(prev_rq->bio, &pb);
        else
                bio_get_first_bvec(prev, &pb);
        if (pb.bv_offset & queue_virt_boundary(q))
                return true;

        /*
         * We don't need to worry about the situation that the merged segment
         * ends in unaligned virt boundary:
         *
         * - if 'pb' ends aligned, the merged segment ends aligned
         * - if 'pb' ends unaligned, the next bio must include
         *   one single bvec of 'nb', otherwise the 'nb' can't
         *   merge with 'pb'
         */
        bio_get_last_bvec(prev, &pb);
        bio_get_first_bvec(next, &nb);
        if (biovec_phys_mergeable(q, &pb, &nb))
                return false;
        return __bvec_gap_to_prev(&q->limits, &pb, nb.bv_offset);
}

static inline bool req_gap_back_merge(struct request *req, struct bio *bio)
{
        return bio_will_gap(req->q, req, req->biotail, bio);
}

static inline bool req_gap_front_merge(struct request *req, struct bio *bio)
{
        return bio_will_gap(req->q, NULL, bio, req->bio);
}

/*
 * The max size one bio can handle is UINT_MAX becasue bvec_iter.bi_size
 * is defined as 'unsigned int', meantime it has to be aligned to with the
 * logical block size, which is the minimum accepted unit by hardware.
 */
static unsigned int bio_allowed_max_sectors(const struct queue_limits *lim)
{
        return round_down(UINT_MAX, lim->logical_block_size) >> SECTOR_SHIFT;
}

static struct bio *bio_split_discard(struct bio *bio,
                                     const struct queue_limits *lim,
                                     unsigned *nsegs, struct bio_set *bs)
{
        unsigned int max_discard_sectors, granularity;
        sector_t tmp;
        unsigned split_sectors;

        *nsegs = 1;

        /* Zero-sector (unknown) and one-sector granularities are the same.  */
        granularity = max(lim->discard_granularity >> 9, 1U);

        max_discard_sectors =
                min(lim->max_discard_sectors, bio_allowed_max_sectors(lim));
        max_discard_sectors -= max_discard_sectors % granularity;

        if (unlikely(!max_discard_sectors)) {
                /* XXX: warn */
                return NULL;
        }

        if (bio_sectors(bio) <= max_discard_sectors)
                return NULL;

        split_sectors = max_discard_sectors;

        /*
         * If the next starting sector would be misaligned, stop the discard at
         * the previous aligned sector.
         */
        tmp = bio->bi_iter.bi_sector + split_sectors -
                ((lim->discard_alignment >> 9) % granularity);
        tmp = sector_div(tmp, granularity);

        if (split_sectors > tmp)
                split_sectors -= tmp;

        return bio_split(bio, split_sectors, GFP_NOIO, bs);
}

static struct bio *bio_split_write_zeroes(struct bio *bio,
                                          const struct queue_limits *lim,
                                          unsigned *nsegs, struct bio_set *bs)
{
        *nsegs = 0;
        if (!lim->max_write_zeroes_sectors)
                return NULL;
        if (bio_sectors(bio) <= lim->max_write_zeroes_sectors)
                return NULL;
        return bio_split(bio, lim->max_write_zeroes_sectors, GFP_NOIO, bs);
}

/*
 * Return the maximum number of sectors from the start of a bio that may be
 * submitted as a single request to a block device. If enough sectors remain,
 * align the end to the physical block size. Otherwise align the end to the
 * logical block size. This approach minimizes the number of non-aligned
 * requests that are submitted to a block device if the start of a bio is not
 * aligned to a physical block boundary.
 */
static inline unsigned get_max_io_size(struct bio *bio,
                                       const struct queue_limits *lim)
{
        unsigned pbs = lim->physical_block_size >> SECTOR_SHIFT;
        unsigned lbs = lim->logical_block_size >> SECTOR_SHIFT;
        unsigned max_sectors = lim->max_sectors, start, end;

        if (lim->chunk_sectors) {
                max_sectors = min(max_sectors,
                        blk_chunk_sectors_left(bio->bi_iter.bi_sector,
                                               lim->chunk_sectors));
        }

        start = bio->bi_iter.bi_sector & (pbs - 1);
        end = (start + max_sectors) & ~(pbs - 1);
        if (end > start)
                return end - start;
        return max_sectors & ~(lbs - 1);
}

/**
 * get_max_segment_size() - maximum number of bytes to add as a single segment
 * @lim: Request queue limits.
 * @start_page: See below.
 * @offset: Offset from @start_page where to add a segment.
 *
 * Returns the maximum number of bytes that can be added as a single segment.
 */
static inline unsigned get_max_segment_size(const struct queue_limits *lim,
                struct page *start_page, unsigned long offset)
{
        unsigned long mask = lim->seg_boundary_mask;

        offset = mask & (page_to_phys(start_page) + offset);

        /*
         * Prevent an overflow if mask = ULONG_MAX and offset = 0 by adding 1
         * after having calculated the minimum.
         */
        return min(mask - offset, (unsigned long)lim->max_segment_size - 1) + 1;
}

/**
 * bvec_split_segs - verify whether or not a bvec should be split in the middle
 * @lim:      [in] queue limits to split based on
 * @bv:       [in] bvec to examine
 * @nsegs:    [in,out] Number of segments in the bio being built. Incremented
 *            by the number of segments from @bv that may be appended to that
 *            bio without exceeding @max_segs
 * @bytes:    [in,out] Number of bytes in the bio being built. Incremented
 *            by the number of bytes from @bv that may be appended to that
 *            bio without exceeding @max_bytes
 * @max_segs: [in] upper bound for *@nsegs
 * @max_bytes: [in] upper bound for *@bytes
 *
 * When splitting a bio, it can happen that a bvec is encountered that is too
 * big to fit in a single segment and hence that it has to be split in the
 * middle. This function verifies whether or not that should happen. The value
 * %true is returned if and only if appending the entire @bv to a bio with
 * *@nsegs segments and *@sectors sectors would make that bio unacceptable for
 * the block driver.
 */
static bool bvec_split_segs(const struct queue_limits *lim,
                const struct bio_vec *bv, unsigned *nsegs, unsigned *bytes,
                unsigned max_segs, unsigned max_bytes)
{
        unsigned max_len = min(max_bytes, UINT_MAX) - *bytes;
        unsigned len = min(bv->bv_len, max_len);
        unsigned total_len = 0;
        unsigned seg_size = 0;

        while (len && *nsegs < max_segs) {
                seg_size = get_max_segment_size(lim, bv->bv_page,
                                                bv->bv_offset + total_len);
                seg_size = min(seg_size, len);

                (*nsegs)++;
                total_len += seg_size;
                len -= seg_size;

                if ((bv->bv_offset + total_len) & lim->virt_boundary_mask)
                        break;
        }

        *bytes += total_len;

        /* tell the caller to split the bvec if it is too big to fit */
        return len > 0 || bv->bv_len > max_len;
}

/**
 * bio_split_rw - split a bio in two bios
 * @bio:  [in] bio to be split
 * @lim:  [in] queue limits to split based on
 * @segs: [out] number of segments in the bio with the first half of the sectors
 * @bs:   [in] bio set to allocate the clone from
 * @max_bytes: [in] maximum number of bytes per bio
 *
 * Clone @bio, update the bi_iter of the clone to represent the first sectors
 * of @bio and update @bio->bi_iter to represent the remaining sectors. The
 * following is guaranteed for the cloned bio:
 * - That it has at most @max_bytes worth of data
 * - That it has at most queue_max_segments(@q) segments.
 *
 * Except for discard requests the cloned bio will point at the bi_io_vec of
 * the original bio. It is the responsibility of the caller to ensure that the
 * original bio is not freed before the cloned bio. The caller is also
 * responsible for ensuring that @bs is only destroyed after processing of the
 * split bio has finished.
 */
static struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
                unsigned *segs, struct bio_set *bs, unsigned max_bytes)
{
        struct bio_vec bv, bvprv, *bvprvp = NULL;
        struct bvec_iter iter;
        unsigned nsegs = 0, bytes = 0;

        bio_for_each_bvec(bv, bio, iter) {
                /*
                 * If the queue doesn't support SG gaps and adding this
                 * offset would create a gap, disallow it.
                 */
                if (bvprvp && bvec_gap_to_prev(lim, bvprvp, bv.bv_offset))
                        goto split;

                if (nsegs < lim->max_segments &&
                    bytes + bv.bv_len <= max_bytes &&
                    bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
                        nsegs++;
                        bytes += bv.bv_len;
                } else {
                        if (bvec_split_segs(lim, &bv, &nsegs, &bytes,
                                        lim->max_segments, max_bytes))
                                goto split;
                }

                bvprv = bv;
                bvprvp = &bvprv;
        }

        *segs = nsegs;
        return NULL;
split:
        /*
         * We can't sanely support splitting for a REQ_NOWAIT bio. End it
         * with EAGAIN if splitting is required and return an error pointer.
         */
        if (bio->bi_opf & REQ_NOWAIT) {
                bio->bi_status = BLK_STS_AGAIN;
                bio_endio(bio);
                return ERR_PTR(-EAGAIN);
        }

        *segs = nsegs;

        /*
         * Individual bvecs might not be logical block aligned. Round down the
         * split size so that each bio is properly block size aligned, even if
         * we do not use the full hardware limits.
         */
        bytes = ALIGN_DOWN(bytes, lim->logical_block_size);

        /*
         * Bio splitting may cause subtle trouble such as hang when doing sync
         * iopoll in direct IO routine. Given performance gain of iopoll for
         * big IO can be trival, disable iopoll when split needed.
         */
        bio_clear_polled(bio);
        return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
}

/**
 * __bio_split_to_limits - split a bio to fit the queue limits
 * @bio:     bio to be split
 * @lim:     queue limits to split based on
 * @nr_segs: returns the number of segments in the returned bio
 *
 * Check if @bio needs splitting based on the queue limits, and if so split off
 * a bio fitting the limits from the beginning of @bio and return it.  @bio is
 * shortened to the remainder and re-submitted.
 *
 * The split bio is allocated from @q->bio_split, which is provided by the
 * block layer.
 */
struct bio *__bio_split_to_limits(struct bio *bio,
                                  const struct queue_limits *lim,
                                  unsigned int *nr_segs)
{
        struct bio_set *bs = &bio->bi_bdev->bd_disk->bio_split;
        struct bio *split;

        switch (bio_op(bio)) {
        case REQ_OP_DISCARD:
        case REQ_OP_SECURE_ERASE:
                split = bio_split_discard(bio, lim, nr_segs, bs);
                break;
        case REQ_OP_WRITE_ZEROES:
                split = bio_split_write_zeroes(bio, lim, nr_segs, bs);
                break;
        default:
                split = bio_split_rw(bio, lim, nr_segs, bs,
                                get_max_io_size(bio, lim) << SECTOR_SHIFT);
                if (IS_ERR(split))
                        return NULL;
                break;
        }

        if (split) {
                /* there isn't chance to merge the split bio */
                split->bi_opf |= REQ_NOMERGE;

                blkcg_bio_issue_init(split);
                bio_chain(split, bio);
                trace_block_split(split, bio->bi_iter.bi_sector);
                submit_bio_noacct(bio);
                return split;
        }
        return bio;
}

/**
 * bio_split_to_limits - split a bio to fit the queue limits
 * @bio:     bio to be split
 *
 * Check if @bio needs splitting based on the queue limits of @bio->bi_bdev, and
 * if so split off a bio fitting the limits from the beginning of @bio and
 * return it.  @bio is shortened to the remainder and re-submitted.
 *
 * The split bio is allocated from @q->bio_split, which is provided by the
 * block layer.
 */
struct bio *bio_split_to_limits(struct bio *bio)
{
        const struct queue_limits *lim = &bdev_get_queue(bio->bi_bdev)->limits;
        unsigned int nr_segs;

        if (bio_may_exceed_limits(bio, lim))
                return __bio_split_to_limits(bio, lim, &nr_segs);
        return bio;
}
EXPORT_SYMBOL(bio_split_to_limits);

unsigned int blk_recalc_rq_segments(struct request *rq)
{
        unsigned int nr_phys_segs = 0;
        unsigned int bytes = 0;
        struct req_iterator iter;
        struct bio_vec bv;

        if (!rq->bio)
                return 0;

        switch (bio_op(rq->bio)) {
        case REQ_OP_DISCARD:
        case REQ_OP_SECURE_ERASE:
                if (queue_max_discard_segments(rq->q) > 1) {
                        struct bio *bio = rq->bio;

                        for_each_bio(bio)
                                nr_phys_segs++;
                        return nr_phys_segs;
                }
                return 1;
        case REQ_OP_WRITE_ZEROES:
                return 0;
        default:
                break;
        }

        rq_for_each_bvec(bv, rq, iter)
                bvec_split_segs(&rq->q->limits, &bv, &nr_phys_segs, &bytes,
                                UINT_MAX, UINT_MAX);
        return nr_phys_segs;
}

static inline struct scatterlist *blk_next_sg(struct scatterlist **sg,
                struct scatterlist *sglist)
{
        if (!*sg)
                return sglist;

        /*
         * If the driver previously mapped a shorter list, we could see a
         * termination bit prematurely unless it fully inits the sg table
         * on each mapping. We KNOW that there must be more entries here
         * or the driver would be buggy, so force clear the termination bit
         * to avoid doing a full sg_init_table() in drivers for each command.
         */
        sg_unmark_end(*sg);
        return sg_next(*sg);
}

static unsigned blk_bvec_map_sg(struct request_queue *q,
                struct bio_vec *bvec, struct scatterlist *sglist,
                struct scatterlist **sg)
{
        unsigned nbytes = bvec->bv_len;
        unsigned nsegs = 0, total = 0;

        while (nbytes > 0) {
                unsigned offset = bvec->bv_offset + total;
                unsigned len = min(get_max_segment_size(&q->limits,
                                   bvec->bv_page, offset), nbytes);
                struct page *page = bvec->bv_page;

                /*
                 * Unfortunately a fair number of drivers barf on scatterlists
                 * that have an offset larger than PAGE_SIZE, despite other
                 * subsystems dealing with that invariant just fine.  For now
                 * stick to the legacy format where we never present those from
                 * the block layer, but the code below should be removed once
                 * these offenders (mostly MMC/SD drivers) are fixed.
                 */
                page += (offset >> PAGE_SHIFT);
                offset &= ~PAGE_MASK;

                *sg = blk_next_sg(sg, sglist);
                sg_set_page(*sg, page, len, offset);

                total += len;
                nbytes -= len;
                nsegs++;
        }

        return nsegs;
}

static inline int __blk_bvec_map_sg(struct bio_vec bv,
                struct scatterlist *sglist, struct scatterlist **sg)
{
        *sg = blk_next_sg(sg, sglist);
        sg_set_page(*sg, bv.bv_page, bv.bv_len, bv.bv_offset);
        return 1;
}

/* only try to merge bvecs into one sg if they are from two bios */
static inline bool
__blk_segment_map_sg_merge(struct request_queue *q, struct bio_vec *bvec,
                           struct bio_vec *bvprv, struct scatterlist **sg)
{

        int nbytes = bvec->bv_len;

        if (!*sg)
                return false;

        if ((*sg)->length + nbytes > queue_max_segment_size(q))
                return false;

        if (!biovec_phys_mergeable(q, bvprv, bvec))
                return false;

        (*sg)->length += nbytes;

        return true;
}

static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
                             struct scatterlist *sglist,
                             struct scatterlist **sg)
{
        struct bio_vec bvec, bvprv = { NULL };
        struct bvec_iter iter;
        int nsegs = 0;
        bool new_bio = false;

        for_each_bio(bio) {
                bio_for_each_bvec(bvec, bio, iter) {
                        /*
                         * Only try to merge bvecs from two bios given we
                         * have done bio internal merge when adding pages
                         * to bio
                         */
                        if (new_bio &&
                            __blk_segment_map_sg_merge(q, &bvec, &bvprv, sg))
                                goto next_bvec;

                        if (bvec.bv_offset + bvec.bv_len <= PAGE_SIZE)
                                nsegs += __blk_bvec_map_sg(bvec, sglist, sg);
                        else
                                nsegs += blk_bvec_map_sg(q, &bvec, sglist, sg);
 next_bvec:
                        new_bio = false;
                }
                if (likely(bio->bi_iter.bi_size)) {
                        bvprv = bvec;
                        new_bio = true;
                }
        }

        return nsegs;
}

/*
 * map a request to scatterlist, return number of sg entries setup. Caller
 * must make sure sg can hold rq->nr_phys_segments entries
 */
int __blk_rq_map_sg(struct request_queue *q, struct request *rq,
                struct scatterlist *sglist, struct scatterlist **last_sg)
{
        int nsegs = 0;

        if (rq->rq_flags & RQF_SPECIAL_PAYLOAD)
                nsegs = __blk_bvec_map_sg(rq->special_vec, sglist, last_sg);
        else if (rq->bio)
                nsegs = __blk_bios_map_sg(q, rq->bio, sglist, last_sg);

        if (*last_sg)
                sg_mark_end(*last_sg);

        /*
         * Something must have been wrong if the figured number of
         * segment is bigger than number of req's physical segments
         */
        WARN_ON(nsegs > blk_rq_nr_phys_segments(rq));

        return nsegs;
}
EXPORT_SYMBOL(__blk_rq_map_sg);

static inline unsigned int blk_rq_get_max_segments(struct request *rq)
{
        if (req_op(rq) == REQ_OP_DISCARD)
                return queue_max_discard_segments(rq->q);
        return queue_max_segments(rq->q);
}

static inline unsigned int blk_rq_get_max_sectors(struct request *rq,
                                                  sector_t offset)
{
        struct request_queue *q = rq->q;
        unsigned int max_sectors;

        if (blk_rq_is_passthrough(rq))
                return q->limits.max_hw_sectors;

        max_sectors = blk_queue_get_max_sectors(q, req_op(rq));
        if (!q->limits.chunk_sectors ||
            req_op(rq) == REQ_OP_DISCARD ||
            req_op(rq) == REQ_OP_SECURE_ERASE)
                return max_sectors;
        return min(max_sectors,
                   blk_chunk_sectors_left(offset, q->limits.chunk_sectors));
}

static inline int ll_new_hw_segment(struct request *req, struct bio *bio,
                unsigned int nr_phys_segs)
{
        if (!blk_cgroup_mergeable(req, bio))
                goto no_merge;

        if (blk_integrity_merge_bio(req->q, req, bio) == false)
                goto no_merge;

        /* discard request merge won't add new segment */
        if (req_op(req) == REQ_OP_DISCARD)
                return 1;

        if (req->nr_phys_segments + nr_phys_segs > blk_rq_get_max_segments(req))
                goto no_merge;

        /*
         * This will form the start of a new hw segment.  Bump both
         * counters.
         */
        req->nr_phys_segments += nr_phys_segs;
        return 1;

no_merge:
        req_set_nomerge(req->q, req);
        return 0;
}

int ll_back_merge_fn(struct request *req, struct bio *bio, unsigned int nr_segs)
{
        if (req_gap_back_merge(req, bio))
                return 0;
        if (blk_integrity_rq(req) &&
            integrity_req_gap_back_merge(req, bio))
                return 0;
        if (!bio_crypt_ctx_back_mergeable(req, bio))
                return 0;
        if (blk_rq_sectors(req) + bio_sectors(bio) >
            blk_rq_get_max_sectors(req, blk_rq_pos(req))) {
                req_set_nomerge(req->q, req);
                return 0;
        }

        return ll_new_hw_segment(req, bio, nr_segs);
}

static int ll_front_merge_fn(struct request *req, struct bio *bio,
                unsigned int nr_segs)
{
        if (req_gap_front_merge(req, bio))
                return 0;
        if (blk_integrity_rq(req) &&
            integrity_req_gap_front_merge(req, bio))
                return 0;
        if (!bio_crypt_ctx_front_mergeable(req, bio))
                return 0;
        if (blk_rq_sectors(req) + bio_sectors(bio) >
            blk_rq_get_max_sectors(req, bio->bi_iter.bi_sector)) {
                req_set_nomerge(req->q, req);
                return 0;
        }

        return ll_new_hw_segment(req, bio, nr_segs);
}

static bool req_attempt_discard_merge(struct request_queue *q, struct request *req,
                struct request *next)
{
        unsigned short segments = blk_rq_nr_discard_segments(req);

        if (segments >= queue_max_discard_segments(q))
                goto no_merge;
        if (blk_rq_sectors(req) + bio_sectors(next->bio) >
            blk_rq_get_max_sectors(req, blk_rq_pos(req)))
                goto no_merge;

        req->nr_phys_segments = segments + blk_rq_nr_discard_segments(next);
        return true;
no_merge:
        req_set_nomerge(q, req);
        return false;
}

static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
                                struct request *next)
{
        int total_phys_segments;

        if (req_gap_back_merge(req, next->bio))
                return 0;

        /*
         * Will it become too large?
         */
        if ((blk_rq_sectors(req) + blk_rq_sectors(next)) >
            blk_rq_get_max_sectors(req, blk_rq_pos(req)))
                return 0;

        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
        if (total_phys_segments > blk_rq_get_max_segments(req))
                return 0;

        if (!blk_cgroup_mergeable(req, next->bio))
                return 0;

        if (blk_integrity_merge_rq(q, req, next) == false)
                return 0;

        if (!bio_crypt_ctx_merge_rq(req, next))
                return 0;

        /* Merge is OK... */
        req->nr_phys_segments = total_phys_segments;
        return 1;
}

/**
 * blk_rq_set_mixed_merge - mark a request as mixed merge
 * @rq: request to mark as mixed merge
 *
 * Description:
 *     @rq is about to be mixed merged.  Make sure the attributes
 *     which can be mixed are set in each bio and mark @rq as mixed
 *     merged.
 */
void blk_rq_set_mixed_merge(struct request *rq)
{
        blk_opf_t ff = rq->cmd_flags & REQ_FAILFAST_MASK;
        struct bio *bio;

        if (rq->rq_flags & RQF_MIXED_MERGE)
                return;

        /*
         * @rq will no longer represent mixable attributes for all the
         * contained bios.  It will just track those of the first one.
         * Distributes the attributs to each bio.
         */
        for (bio = rq->bio; bio; bio = bio->bi_next) {
                WARN_ON_ONCE((bio->bi_opf & REQ_FAILFAST_MASK) &&
                             (bio->bi_opf & REQ_FAILFAST_MASK) != ff);
                bio->bi_opf |= ff;
        }
        rq->rq_flags |= RQF_MIXED_MERGE;
}

static void blk_account_io_merge_request(struct request *req)
{
        if (blk_do_io_stat(req)) {
                part_stat_lock();
                part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
                part_stat_unlock();
        }
}

static enum elv_merge blk_try_req_merge(struct request *req,
                                        struct request *next)
{
        if (blk_discard_mergable(req))
                return ELEVATOR_DISCARD_MERGE;
        else if (blk_rq_pos(req) + blk_rq_sectors(req) == blk_rq_pos(next))
                return ELEVATOR_BACK_MERGE;

        return ELEVATOR_NO_MERGE;
}

/*
 * For non-mq, this has to be called with the request spinlock acquired.
 * For mq with scheduling, the appropriate queue wide lock should be held.
 */
static struct request *attempt_merge(struct request_queue *q,
                                     struct request *req, struct request *next)
{
        if (!rq_mergeable(req) || !rq_mergeable(next))
                return NULL;

        if (req_op(req) != req_op(next))
                return NULL;

        if (rq_data_dir(req) != rq_data_dir(next))
                return NULL;

        if (req->ioprio != next->ioprio)
                return NULL;

        /*
         * If we are allowed to merge, then append bio list
         * from next to rq and release next. merge_requests_fn
         * will have updated segment counts, update sector
         * counts here. Handle DISCARDs separately, as they
         * have separate settings.
         */

        switch (blk_try_req_merge(req, next)) {
        case ELEVATOR_DISCARD_MERGE:
                if (!req_attempt_discard_merge(q, req, next))
                        return NULL;
                break;
        case ELEVATOR_BACK_MERGE:
                if (!ll_merge_requests_fn(q, req, next))
                        return NULL;
                break;
        default:
                return NULL;
        }

        /*
         * If failfast settings disagree or any of the two is already
         * a mixed merge, mark both as mixed before proceeding.  This
         * makes sure that all involved bios have mixable attributes
         * set properly.
         */
        if (((req->rq_flags | next->rq_flags) & RQF_MIXED_MERGE) ||
            (req->cmd_flags & REQ_FAILFAST_MASK) !=
            (next->cmd_flags & REQ_FAILFAST_MASK)) {
                blk_rq_set_mixed_merge(req);
                blk_rq_set_mixed_merge(next);
        }

        /*
         * At this point we have either done a back merge or front merge. We
         * need the smaller start_time_ns of the merged requests to be the
         * current request for accounting purposes.
         */
        if (next->start_time_ns < req->start_time_ns)
                req->start_time_ns = next->start_time_ns;

        req->biotail->bi_next = next->bio;
        req->biotail = next->biotail;

        req->__data_len += blk_rq_bytes(next);

        if (!blk_discard_mergable(req))
                elv_merge_requests(q, req, next);

        /*
         * 'next' is going away, so update stats accordingly
         */
        blk_account_io_merge_request(next);

        trace_block_rq_merge(next);

        /*
         * ownership of bio passed from next to req, return 'next' for
         * the caller to free
         */
        next->bio = NULL;
        return next;
}

static struct request *attempt_back_merge(struct request_queue *q,
                struct request *rq)
{
        struct request *next = elv_latter_request(q, rq);

        if (next)
                return attempt_merge(q, rq, next);

        return NULL;
}

static struct request *attempt_front_merge(struct request_queue *q,
                struct request *rq)
{
        struct request *prev = elv_former_request(q, rq);

        if (prev)
                return attempt_merge(q, prev, rq);

        return NULL;
}

/*
 * Try to merge 'next' into 'rq'. Return true if the merge happened, false
 * otherwise. The caller is responsible for freeing 'next' if the merge
 * happened.
 */
bool blk_attempt_req_merge(struct request_queue *q, struct request *rq,
                           struct request *next)
{
        return attempt_merge(q, rq, next);
}

bool blk_rq_merge_ok(struct request *rq, struct bio *bio)
{
        if (!rq_mergeable(rq) || !bio_mergeable(bio))
                return false;

        if (req_op(rq) != bio_op(bio))
                return false;

        /* different data direction or already started, don't merge */
        if (bio_data_dir(bio) != rq_data_dir(rq))
                return false;

        /* don't merge across cgroup boundaries */
        if (!blk_cgroup_mergeable(rq, bio))
                return false;

        /* only merge integrity protected bio into ditto rq */
        if (blk_integrity_merge_bio(rq->q, rq, bio) == false)
                return false;

        /* Only merge if the crypt contexts are compatible */
        if (!bio_crypt_rq_ctx_compatible(rq, bio))
                return false;

        if (rq->ioprio != bio_prio(bio))
                return false;

        return true;
}

enum elv_merge blk_try_merge(struct request *rq, struct bio *bio)
{
        if (blk_discard_mergable(rq))
                return ELEVATOR_DISCARD_MERGE;
        else if (blk_rq_pos(rq) + blk_rq_sectors(rq) == bio->bi_iter.bi_sector)
                return ELEVATOR_BACK_MERGE;
        else if (blk_rq_pos(rq) - bio_sectors(bio) == bio->bi_iter.bi_sector)
                return ELEVATOR_FRONT_MERGE;
        return ELEVATOR_NO_MERGE;
}

static void blk_account_io_merge_bio(struct request *req)
{
        if (!blk_do_io_stat(req))
                return;

        part_stat_lock();
        part_stat_inc(req->part, merges[op_stat_group(req_op(req))]);
        part_stat_unlock();
}

enum bio_merge_status {
        BIO_MERGE_OK,
        BIO_MERGE_NONE,
        BIO_MERGE_FAILED,
};

static enum bio_merge_status bio_attempt_back_merge(struct request *req,
                struct bio *bio, unsigned int nr_segs)
{
        const blk_opf_t ff = bio->bi_opf & REQ_FAILFAST_MASK;

        if (!ll_back_merge_fn(req, bio, nr_segs))
                return BIO_MERGE_FAILED;

        trace_block_bio_backmerge(bio);
        rq_qos_merge(req->q, req, bio);

        if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
                blk_rq_set_mixed_merge(req);

        req->biotail->bi_next = bio;
        req->biotail = bio;
        req->__data_len += bio->bi_iter.bi_size;

        bio_crypt_free_ctx(bio);

        blk_account_io_merge_bio(req);
        return BIO_MERGE_OK;
}

static enum bio_merge_status bio_attempt_front_merge(struct request *req,
                struct bio *bio, unsigned int nr_segs)
{
        const blk_opf_t ff = bio->bi_opf & REQ_FAILFAST_MASK;

        if (!ll_front_merge_fn(req, bio, nr_segs))
                return BIO_MERGE_FAILED;

        trace_block_bio_frontmerge(bio);
        rq_qos_merge(req->q, req, bio);

        if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
                blk_rq_set_mixed_merge(req);

        bio->bi_next = req->bio;
        req->bio = bio;

        req->__sector = bio->bi_iter.bi_sector;
        req->__data_len += bio->bi_iter.bi_size;

        bio_crypt_do_front_merge(req, bio);

        blk_account_io_merge_bio(req);
        return BIO_MERGE_OK;
}

static enum bio_merge_status bio_attempt_discard_merge(struct request_queue *q,
                struct request *req, struct bio *bio)
{
        unsigned short segments = blk_rq_nr_discard_segments(req);

        if (segments >= queue_max_discard_segments(q))
                goto no_merge;
        if (blk_rq_sectors(req) + bio_sectors(bio) >
            blk_rq_get_max_sectors(req, blk_rq_pos(req)))
                goto no_merge;

        rq_qos_merge(q, req, bio);

        req->biotail->bi_next = bio;
        req->biotail = bio;
        req->__data_len += bio->bi_iter.bi_size;
        req->nr_phys_segments = segments + 1;

        blk_account_io_merge_bio(req);
        return BIO_MERGE_OK;
no_merge:
        req_set_nomerge(q, req);
        return BIO_MERGE_FAILED;
}

static enum bio_merge_status blk_attempt_bio_merge(struct request_queue *q,
                                                   struct request *rq,
                                                   struct bio *bio,
                                                   unsigned int nr_segs,
                                                   bool sched_allow_merge)
{
        if (!blk_rq_merge_ok(rq, bio))
                return BIO_MERGE_NONE;

        switch (blk_try_merge(rq, bio)) {
        case ELEVATOR_BACK_MERGE:
                if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
                        return bio_attempt_back_merge(rq, bio, nr_segs);
                break;
        case ELEVATOR_FRONT_MERGE:
                if (!sched_allow_merge || blk_mq_sched_allow_merge(q, rq, bio))
                        return bio_attempt_front_merge(rq, bio, nr_segs);
                break;
        case ELEVATOR_DISCARD_MERGE:
                return bio_attempt_discard_merge(q, rq, bio);
        default:
                return BIO_MERGE_NONE;
        }

        return BIO_MERGE_FAILED;
}

/**
 * blk_attempt_plug_merge - try to merge with %current's plugged list
 * @q: request_queue new bio is being queued at
 * @bio: new bio being queued
 * @nr_segs: number of segments in @bio
 * from the passed in @q already in the plug list
 *
 * Determine whether @bio being queued on @q can be merged with the previous
 * request on %current's plugged list.  Returns %true if merge was successful,
 * otherwise %false.
 *
 * Plugging coalesces IOs from the same issuer for the same purpose without
 * going through @q->queue_lock.  As such it's more of an issuing mechanism
 * than scheduling, and the request, while may have elvpriv data, is not
 * added on the elevator at this point.  In addition, we don't have
 * reliable access to the elevator outside queue lock.  Only check basic
 * merging parameters without querying the elevator.
 *
 * Caller must ensure !blk_queue_nomerges(q) beforehand.
 */
bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
                unsigned int nr_segs)
{
        struct blk_plug *plug;
        struct request *rq;

        plug = blk_mq_plug(bio);
        if (!plug || rq_list_empty(plug->mq_list))
                return false;

        rq_list_for_each(&plug->mq_list, rq) {
                if (rq->q == q) {
                        if (blk_attempt_bio_merge(q, rq, bio, nr_segs, false) ==
                            BIO_MERGE_OK)
                                return true;
                        break;
                }

                /*
                 * Only keep iterating plug list for merges if we have multiple
                 * queues
                 */
                if (!plug->multiple_queues)
                        break;
        }
        return false;
}

/*
 * Iterate list of requests and see if we can merge this bio with any
 * of them.
 */
bool blk_bio_list_merge(struct request_queue *q, struct list_head *list,
                        struct bio *bio, unsigned int nr_segs)
{
        struct request *rq;
        int checked = 8;

        list_for_each_entry_reverse(rq, list, queuelist) {
                if (!checked--)
                        break;

                switch (blk_attempt_bio_merge(q, rq, bio, nr_segs, true)) {
                case BIO_MERGE_NONE:
                        continue;
                case BIO_MERGE_OK:
                        return true;
                case BIO_MERGE_FAILED:
                        return false;
                }

        }

        return false;
}
EXPORT_SYMBOL_GPL(blk_bio_list_merge);

bool blk_mq_sched_try_merge(struct request_queue *q, struct bio *bio,
                unsigned int nr_segs, struct request **merged_request)
{
        struct request *rq;

        switch (elv_merge(q, &rq, bio)) {
        case ELEVATOR_BACK_MERGE:
                if (!blk_mq_sched_allow_merge(q, rq, bio))
                        return false;
                if (bio_attempt_back_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
                        return false;
                *merged_request = attempt_back_merge(q, rq);
                if (!*merged_request)
                        elv_merged_request(q, rq, ELEVATOR_BACK_MERGE);
                return true;
        case ELEVATOR_FRONT_MERGE:
                if (!blk_mq_sched_allow_merge(q, rq, bio))
                        return false;
                if (bio_attempt_front_merge(rq, bio, nr_segs) != BIO_MERGE_OK)
                        return false;
                *merged_request = attempt_front_merge(q, rq);
                if (!*merged_request)
                        elv_merged_request(q, rq, ELEVATOR_FRONT_MERGE);
                return true;
        case ELEVATOR_DISCARD_MERGE:
                return bio_attempt_discard_merge(q, rq, bio) == BIO_MERGE_OK;
        default:
                return false;
        }
}
EXPORT_SYMBOL_GPL(blk_mq_sched_try_merge);