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block: Add blk_bio_map_sg() helper

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Add a helper to map a bio to a scatterlist, modelled after
blk_rq_map_sg.

This helper is useful for any driver that wants to create
a scatterlist from its ->make_request_fn method.

Changes in v2:
 - Use __blk_segment_map_sg to avoid duplicated code
 - Add cocbook style function comment

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Tejun Heo <tj@kernel.org>
Cc: Shaohua Li <shli@kernel.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Asias He 2012-08-02 23:42:04 +02:00 committed by Jens Axboe
parent 963ab9e5da
commit 85b9f66a41
2 changed files with 39 additions and 0 deletions
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37
block/blk-merge.c
View file

@ -209,6 +209,43 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
}
EXPORT_SYMBOL(blk_rq_map_sg);
/**
* blk_bio_map_sg - map a bio to a scatterlist
* @q: request_queue in question
* @bio: bio being mapped
* @sglist: scatterlist being mapped
*
* Note:
* Caller must make sure sg can hold bio->bi_phys_segments entries
*
* Will return the number of sg entries setup
*/
int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
struct scatterlist *sglist)
{
struct bio_vec *bvec, *bvprv;
struct scatterlist *sg;
int nsegs, cluster;
unsigned long i;
nsegs = 0;
cluster = blk_queue_cluster(q);
bvprv = NULL;
sg = NULL;
bio_for_each_segment(bvec, bio, i) {
__blk_segment_map_sg(q, bvec, sglist, &bvprv, &sg,
&nsegs, &cluster);
} /* segments in bio */
if (sg)
sg_mark_end(sg);
BUG_ON(bio->bi_phys_segments && nsegs > bio->bi_phys_segments);
return nsegs;
}
EXPORT_SYMBOL(blk_bio_map_sg);
static inline int ll_new_hw_segment(struct request_queue *q,
struct request *req,
struct bio *bio)

2
include/linux/blkdev.h
View file

@ -894,6 +894,8 @@ extern void blk_queue_flush_queueable(struct request_queue *q, bool queueable);
extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
extern int blk_rq_map_sg(struct request_queue *, struct request *, struct scatterlist *);
extern int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
struct scatterlist *sglist);
extern void blk_dump_rq_flags(struct request *, char *);
extern long nr_blockdev_pages(void);