/*
 * 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/scatterlist.h>

#include "blk.h"

static unsigned int __blk_recalc_rq_segments(struct request_queue *q,
                                             struct bio *bio)
{
        unsigned int phys_size;
        struct bio_vec *bv, *bvprv = NULL;
        int cluster, i, high, highprv = 1;
        unsigned int seg_size, nr_phys_segs;
        struct bio *fbio, *bbio;

        if (!bio)
                return 0;

        fbio = bio;
        cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
        seg_size = 0;
        phys_size = nr_phys_segs = 0;
        for_each_bio(bio) {
                bio_for_each_segment(bv, bio, i) {
                        /*
                         * the trick here is making sure that a high page is
                         * never considered part of another segment, since that
                         * might change with the bounce page.
                         */
                        high = page_to_pfn(bv->bv_page) > queue_bounce_pfn(q);
                        if (high || highprv)
                                goto new_segment;
                        if (cluster) {
                                if (seg_size + bv->bv_len
                                    > queue_max_segment_size(q))
                                        goto new_segment;
                                if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
                                        goto new_segment;
                                if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
                                        goto new_segment;

                                seg_size += bv->bv_len;
                                bvprv = bv;
                                continue;
                        }
new_segment:
                        if (nr_phys_segs == 1 && seg_size >
                            fbio->bi_seg_front_size)
                                fbio->bi_seg_front_size = seg_size;

                        nr_phys_segs++;
                        bvprv = bv;
                        seg_size = bv->bv_len;
                        highprv = high;
                }
                bbio = bio;
        }

        if (nr_phys_segs == 1 && seg_size > fbio->bi_seg_front_size)
                fbio->bi_seg_front_size = seg_size;
        if (seg_size > bbio->bi_seg_back_size)
                bbio->bi_seg_back_size = seg_size;

        return nr_phys_segs;
}

void blk_recalc_rq_segments(struct request *rq)
{
        rq->nr_phys_segments = __blk_recalc_rq_segments(rq->q, rq->bio);
}

void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
        struct bio *nxt = bio->bi_next;

        bio->bi_next = NULL;
        bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio);
        bio->bi_next = nxt;
        bio->bi_flags |= (1 << BIO_SEG_VALID);
}
EXPORT_SYMBOL(blk_recount_segments);

static int blk_phys_contig_segment(struct request_queue *q, struct bio *bio,
                                   struct bio *nxt)
{
        if (!test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags))
                return 0;

        if (bio->bi_seg_back_size + nxt->bi_seg_front_size >
            queue_max_segment_size(q))
                return 0;

        if (!bio_has_data(bio))
                return 1;

        if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
                return 0;

        /*
         * bio and nxt are contiguous in memory; check if the queue allows
         * these two to be merged into one
         */
        if (BIO_SEG_BOUNDARY(q, bio, nxt))
                return 1;

        return 0;
}

/*
 * 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 bio_vec *bvec, *bvprv;
        struct req_iterator iter;
        struct scatterlist *sg;
        int nsegs, cluster;

        nsegs = 0;
        cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);

        /*
         * for each bio in rq
         */
        bvprv = NULL;
        sg = NULL;
        rq_for_each_segment(bvec, rq, iter) {
                int nbytes = bvec->bv_len;

                if (bvprv && cluster) {
                        if (sg->length + nbytes > queue_max_segment_size(q))
                                goto new_segment;

                        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bvec))
                                goto new_segment;
                        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bvec))
                                goto new_segment;

                        sg->length += nbytes;
                } else {
new_segment:
                        if (!sg)
                                sg = sglist;
                        else {
                                /*
                                 * 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->page_link &= ~0x02;
                                sg = sg_next(sg);
                        }

                        sg_set_page(sg, bvec->bv_page, nbytes, bvec->bv_offset);
                        nsegs++;
                }
                bvprv = bvec;
        } /* segments in rq */


        if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
            (blk_rq_bytes(rq) & q->dma_pad_mask)) {
                unsigned int pad_len =
                        (q->dma_pad_mask & ~blk_rq_bytes(rq)) + 1;

                sg->length += pad_len;
                rq->extra_len += pad_len;
        }

        if (q->dma_drain_size && q->dma_drain_needed(rq)) {
                if (rq->cmd_flags & REQ_RW)
                        memset(q->dma_drain_buffer, 0, q->dma_drain_size);

                sg->page_link &= ~0x02;
                sg = sg_next(sg);
                sg_set_page(sg, virt_to_page(q->dma_drain_buffer),
                            q->dma_drain_size,
                            ((unsigned long)q->dma_drain_buffer) &
                            (PAGE_SIZE - 1));
                nsegs++;
                rq->extra_len += q->dma_drain_size;
        }

        if (sg)
                sg_mark_end(sg);

        return nsegs;
}
EXPORT_SYMBOL(blk_rq_map_sg);

static inline int ll_new_hw_segment(struct request_queue *q,
                                    struct request *req,
                                    struct bio *bio)
{
        int nr_phys_segs = bio_phys_segments(q, bio);

        if (req->nr_phys_segments + nr_phys_segs > queue_max_hw_segments(q) ||
            req->nr_phys_segments + nr_phys_segs > queue_max_phys_segments(q)) {
                req->cmd_flags |= REQ_NOMERGE;
                if (req == q->last_merge)
                        q->last_merge = NULL;
                return 0;
        }

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

int ll_back_merge_fn(struct request_queue *q, struct request *req,
                     struct bio *bio)
{
        unsigned short max_sectors;

        if (unlikely(blk_pc_request(req)))
                max_sectors = queue_max_hw_sectors(q);
        else
                max_sectors = queue_max_sectors(q);

        if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
                req->cmd_flags |= REQ_NOMERGE;
                if (req == q->last_merge)
                        q->last_merge = NULL;
                return 0;
        }
        if (!bio_flagged(req->biotail, BIO_SEG_VALID))
                blk_recount_segments(q, req->biotail);
        if (!bio_flagged(bio, BIO_SEG_VALID))
                blk_recount_segments(q, bio);

        return ll_new_hw_segment(q, req, bio);
}

int ll_front_merge_fn(struct request_queue *q, struct request *req,
                      struct bio *bio)
{
        unsigned short max_sectors;

        if (unlikely(blk_pc_request(req)))
                max_sectors = queue_max_hw_sectors(q);
        else
                max_sectors = queue_max_sectors(q);


        if (blk_rq_sectors(req) + bio_sectors(bio) > max_sectors) {
                req->cmd_flags |= REQ_NOMERGE;
                if (req == q->last_merge)
                        q->last_merge = NULL;
                return 0;
        }
        if (!bio_flagged(bio, BIO_SEG_VALID))
                blk_recount_segments(q, bio);
        if (!bio_flagged(req->bio, BIO_SEG_VALID))
                blk_recount_segments(q, req->bio);

        return ll_new_hw_segment(q, req, bio);
}

static int ll_merge_requests_fn(struct request_queue *q, struct request *req,
                                struct request *next)
{
        int total_phys_segments;
        unsigned int seg_size =
                req->biotail->bi_seg_back_size + next->bio->bi_seg_front_size;

        /*
         * First check if the either of the requests are re-queued
         * requests.  Can't merge them if they are.
         */
        if (req->special || next->special)
                return 0;

        /*
         * Will it become too large?
         */
        if ((blk_rq_sectors(req) + blk_rq_sectors(next)) > queue_max_sectors(q))
                return 0;

        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
        if (blk_phys_contig_segment(q, req->biotail, next->bio)) {
                if (req->nr_phys_segments == 1)
                        req->bio->bi_seg_front_size = seg_size;
                if (next->nr_phys_segments == 1)
                        next->biotail->bi_seg_back_size = seg_size;
                total_phys_segments--;
        }

        if (total_phys_segments > queue_max_phys_segments(q))
                return 0;

        if (total_phys_segments > queue_max_hw_segments(q))
                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)
{
        unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
        struct bio *bio;

        if (rq->cmd_flags & REQ_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_rw & REQ_FAILFAST_MASK) &&
                             (bio->bi_rw & REQ_FAILFAST_MASK) != ff);
                bio->bi_rw |= ff;
        }
        rq->cmd_flags |= REQ_MIXED_MERGE;
}

static void blk_account_io_merge(struct request *req)
{
        if (blk_do_io_stat(req)) {
                struct hd_struct *part;
                int cpu;

                cpu = part_stat_lock();
                part = disk_map_sector_rcu(req->rq_disk, blk_rq_pos(req));

                part_round_stats(cpu, part);
                part_dec_in_flight(part, rq_data_dir(req));

                part_stat_unlock();
        }
}

/*
 * Has to be called with the request spinlock acquired
 */
static int attempt_merge(struct request_queue *q, struct request *req,
                          struct request *next)
{
        if (!rq_mergeable(req) || !rq_mergeable(next))
                return 0;

        /*
         * not contiguous
         */
        if (blk_rq_pos(req) + blk_rq_sectors(req) != blk_rq_pos(next))
                return 0;

        if (rq_data_dir(req) != rq_data_dir(next)
            || req->rq_disk != next->rq_disk
            || next->special)
                return 0;

        if (blk_integrity_rq(req) != blk_integrity_rq(next))
                return 0;

        /*
         * 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.
         */
        if (!ll_merge_requests_fn(q, req, next))
                return 0;

        /*
         * 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->cmd_flags | next->cmd_flags) & REQ_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 of
         * the merged requests to be the current request
         * for accounting purposes.
         */
        if (time_after(req->start_time, next->start_time))
                req->start_time = next->start_time;

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

        req->__data_len += blk_rq_bytes(next);

        elv_merge_requests(q, req, next);

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

        req->ioprio = ioprio_best(req->ioprio, next->ioprio);
        if (blk_rq_cpu_valid(next))
                req->cpu = next->cpu;

        /* owner-ship of bio passed from next to req */
        next->bio = NULL;
        __blk_put_request(q, next);
        return 1;
}

int 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 0;
}

int 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 0;
}