/*
 * 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"

void blk_recalc_rq_sectors(struct request *rq, int nsect)
{
        if (blk_fs_request(rq)) {
                rq->hard_sector += nsect;
                rq->hard_nr_sectors -= nsect;

                /*
                 * Move the I/O submission pointers ahead if required.
                 */
                if ((rq->nr_sectors >= rq->hard_nr_sectors) &&
                    (rq->sector <= rq->hard_sector)) {
                        rq->sector = rq->hard_sector;
                        rq->nr_sectors = rq->hard_nr_sectors;
                        rq->hard_cur_sectors = bio_cur_sectors(rq->bio);
                        rq->current_nr_sectors = rq->hard_cur_sectors;
                        rq->buffer = bio_data(rq->bio);
                }

                /*
                 * if total number of sectors is less than the first segment
                 * size, something has gone terribly wrong
                 */
                if (rq->nr_sectors < rq->current_nr_sectors) {
                        printk(KERN_ERR "blk: request botched\n");
                        rq->nr_sectors = rq->current_nr_sectors;
                }
        }
}

void blk_recalc_rq_segments(struct request *rq)
{
        int nr_phys_segs;
        int nr_hw_segs;
        unsigned int phys_size;
        unsigned int hw_size;
        struct bio_vec *bv, *bvprv = NULL;
        int seg_size;
        int hw_seg_size;
        int cluster;
        struct req_iterator iter;
        int high, highprv = 1;
        struct request_queue *q = rq->q;

        if (!rq->bio)
                return;

        cluster = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);
        hw_seg_size = seg_size = 0;
        phys_size = hw_size = nr_phys_segs = nr_hw_segs = 0;
        rq_for_each_segment(bv, rq, iter) {
                /*
                 * 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) > q->bounce_pfn;
                if (high || highprv)
                        goto new_hw_segment;
                if (cluster) {
                        if (seg_size + bv->bv_len > q->max_segment_size)
                                goto new_segment;
                        if (!BIOVEC_PHYS_MERGEABLE(bvprv, bv))
                                goto new_segment;
                        if (!BIOVEC_SEG_BOUNDARY(q, bvprv, bv))
                                goto new_segment;
                        if (BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
                                goto new_hw_segment;

                        seg_size += bv->bv_len;
                        hw_seg_size += bv->bv_len;
                        bvprv = bv;
                        continue;
                }
new_segment:
                if (BIOVEC_VIRT_MERGEABLE(bvprv, bv) &&
                    !BIOVEC_VIRT_OVERSIZE(hw_seg_size + bv->bv_len))
                        hw_seg_size += bv->bv_len;
                else {
new_hw_segment:
                        if (nr_hw_segs == 1 &&
                            hw_seg_size > rq->bio->bi_hw_front_size)
                                rq->bio->bi_hw_front_size = hw_seg_size;
                        hw_seg_size = BIOVEC_VIRT_START_SIZE(bv) + bv->bv_len;
                        nr_hw_segs++;
                }

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

        if (nr_hw_segs == 1 &&
            hw_seg_size > rq->bio->bi_hw_front_size)
                rq->bio->bi_hw_front_size = hw_seg_size;
        if (hw_seg_size > rq->biotail->bi_hw_back_size)
                rq->biotail->bi_hw_back_size = hw_seg_size;
        rq->nr_phys_segments = nr_phys_segs;
        rq->nr_hw_segments = nr_hw_segs;
}

void blk_recount_segments(struct request_queue *q, struct bio *bio)
{
        struct request rq;
        struct bio *nxt = bio->bi_next;
        rq.q = q;
        rq.bio = rq.biotail = bio;
        bio->bi_next = NULL;
        blk_recalc_rq_segments(&rq);
        bio->bi_next = nxt;
        bio->bi_phys_segments = rq.nr_phys_segments;
        bio->bi_hw_segments = rq.nr_hw_segments;
        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 (!(q->queue_flags & (1 << QUEUE_FLAG_CLUSTER)))
                return 0;

        if (!BIOVEC_PHYS_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)))
                return 0;
        if (bio->bi_size + nxt->bi_size > q->max_segment_size)
                return 0;

        /*
         * bio and nxt are contigous 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;
}

static int blk_hw_contig_segment(struct request_queue *q, struct bio *bio,
                                 struct bio *nxt)
{
        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
                blk_recount_segments(q, bio);
        if (unlikely(!bio_flagged(nxt, BIO_SEG_VALID)))
                blk_recount_segments(q, nxt);
        if (!BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(nxt)) ||
            BIOVEC_VIRT_OVERSIZE(bio->bi_hw_back_size + nxt->bi_hw_front_size))
                return 0;
        if (bio->bi_hw_back_size + nxt->bi_hw_front_size > q->max_segment_size)
                return 0;

        return 1;
}

/*
 * 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 = q->queue_flags & (1 << QUEUE_FLAG_CLUSTER);

        /*
         * 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 > q->max_segment_size)
                                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 (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_mergeable(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 > q->max_phys_segments) {
                req->cmd_flags |= REQ_NOMERGE;
                if (req == q->last_merge)
                        q->last_merge = NULL;
                return 0;
        }

        /*
         * A hw segment is just getting larger, bump just the phys
         * counter.
         */
        req->nr_phys_segments += nr_phys_segs;
        return 1;
}

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

        if (req->nr_hw_segments + nr_hw_segs > q->max_hw_segments
            || req->nr_phys_segments + nr_phys_segs > q->max_phys_segments) {
                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_hw_segments += nr_hw_segs;
        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;
        int len;

        if (unlikely(blk_pc_request(req)))
                max_sectors = q->max_hw_sectors;
        else
                max_sectors = q->max_sectors;

        if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
                req->cmd_flags |= REQ_NOMERGE;
                if (req == q->last_merge)
                        q->last_merge = NULL;
                return 0;
        }
        if (unlikely(!bio_flagged(req->biotail, BIO_SEG_VALID)))
                blk_recount_segments(q, req->biotail);
        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
                blk_recount_segments(q, bio);
        len = req->biotail->bi_hw_back_size + bio->bi_hw_front_size;
        if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(req->biotail), __BVEC_START(bio))
            && !BIOVEC_VIRT_OVERSIZE(len)) {
                int mergeable =  ll_new_mergeable(q, req, bio);

                if (mergeable) {
                        if (req->nr_hw_segments == 1)
                                req->bio->bi_hw_front_size = len;
                        if (bio->bi_hw_segments == 1)
                                bio->bi_hw_back_size = len;
                }
                return mergeable;
        }

        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;
        int len;

        if (unlikely(blk_pc_request(req)))
                max_sectors = q->max_hw_sectors;
        else
                max_sectors = q->max_sectors;


        if (req->nr_sectors + bio_sectors(bio) > max_sectors) {
                req->cmd_flags |= REQ_NOMERGE;
                if (req == q->last_merge)
                        q->last_merge = NULL;
                return 0;
        }
        len = bio->bi_hw_back_size + req->bio->bi_hw_front_size;
        if (unlikely(!bio_flagged(bio, BIO_SEG_VALID)))
                blk_recount_segments(q, bio);
        if (unlikely(!bio_flagged(req->bio, BIO_SEG_VALID)))
                blk_recount_segments(q, req->bio);
        if (BIOVEC_VIRT_MERGEABLE(__BVEC_END(bio), __BVEC_START(req->bio)) &&
            !BIOVEC_VIRT_OVERSIZE(len)) {
                int mergeable =  ll_new_mergeable(q, req, bio);

                if (mergeable) {
                        if (bio->bi_hw_segments == 1)
                                bio->bi_hw_front_size = len;
                        if (req->nr_hw_segments == 1)
                                req->biotail->bi_hw_back_size = len;
                }
                return mergeable;
        }

        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;
        int total_hw_segments;

        /*
         * 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 ((req->nr_sectors + next->nr_sectors) > q->max_sectors)
                return 0;

        total_phys_segments = req->nr_phys_segments + next->nr_phys_segments;
        if (blk_phys_contig_segment(q, req->biotail, next->bio))
                total_phys_segments--;

        if (total_phys_segments > q->max_phys_segments)
                return 0;

        total_hw_segments = req->nr_hw_segments + next->nr_hw_segments;
        if (blk_hw_contig_segment(q, req->biotail, next->bio)) {
                int len = req->biotail->bi_hw_back_size +
                                next->bio->bi_hw_front_size;
                /*
                 * propagate the combined length to the end of the requests
                 */
                if (req->nr_hw_segments == 1)
                        req->bio->bi_hw_front_size = len;
                if (next->nr_hw_segments == 1)
                        next->biotail->bi_hw_back_size = len;
                total_hw_segments--;
        }

        if (total_hw_segments > q->max_hw_segments)
                return 0;

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

/*
 * 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 (req->sector + req->nr_sectors != next->sector)
                return 0;

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

        /*
         * 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->nr_sectors = req->hard_nr_sectors += next->hard_nr_sectors;

        elv_merge_requests(q, req, next);

        if (req->rq_disk) {
                struct hd_struct *part
                        = get_part(req->rq_disk, req->sector);
                disk_round_stats(req->rq_disk);
                req->rq_disk->in_flight--;
                if (part) {
                        part_round_stats(part);
                        part->in_flight--;
                }
        }

        req->ioprio = ioprio_best(req->ioprio, next->ioprio);

        __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;
}