/*
   * 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) || blk_discard_rq(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
  ");

  			rq->nr_sectors = rq->current_nr_sectors;
  		}
  	}
  }
  
  void blk_recalc_rq_segments(struct request *rq)
  {
  	int nr_phys_segs;

  	unsigned int phys_size;

  	struct bio_vec *bv, *bvprv = NULL;
  	int seg_size;

  	int cluster;
  	struct req_iterator iter;
  	int high, highprv = 1;
  	struct request_queue *q = rq->q;
  
  	if (!rq->bio)
  		return;

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

  	seg_size = 0;
  	phys_size = nr_phys_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_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;

  
  			seg_size += bv->bv_len;

  			bvprv = bv;
  			continue;
  		}
  new_segment:

  		if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
  			rq->bio->bi_seg_front_size = seg_size;

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

  	if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)
  		rq->bio->bi_seg_front_size = seg_size;
  	if (seg_size > rq->biotail->bi_seg_back_size)
  		rq->biotail->bi_seg_back_size = seg_size;

  	rq->nr_phys_segments = nr_phys_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_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 >
  	    q->max_segment_size)

  		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 > 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 (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
  	    (rq->data_len & q->dma_pad_mask)) {
  		unsigned int pad_len = (q->dma_pad_mask & ~rq->data_len) + 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 > 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_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 = 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 (!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 = 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 (!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 ((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)) {
  		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 > q->max_phys_segments)
  		return 0;

  	if (total_phys_segments > q->max_hw_segments)

  		return 0;
  
  	/* Merge is OK... */
  	req->nr_phys_segments = total_phys_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 (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;
  
  	/*
  	 * 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;

  		int cpu;

  		cpu = part_stat_lock();

  		part = disk_map_sector_rcu(req->rq_disk, req->sector);

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

  		part_stat_unlock();

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

  	if (blk_rq_cpu_valid(next))
  		req->cpu = next->cpu;

  
  	__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;
  }