[RFC v2 1/3] block: Introduce blk_bio_map_sg() to map one bio

From: Baolin Wang
Date: Fri May 27 2016 - 07:12:08 EST


In dm-crypt, it need to map one bio to scatterlist for improving the
hardware engine encryption efficiency. Thus this patch introduces the
blk_bio_map_sg() function to map one bio with scatterlists.

For avoiding the duplicated code in __blk_bios_map_sg() function, add
one parameter to distinguish bio map or request map.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxx>
---
block/blk-merge.c | 36 +++++++++++++++++++++++++++++++-----
include/linux/blkdev.h | 2 ++
2 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 2613531..badae44 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -376,7 +376,7 @@ new_segment:

static int __blk_bios_map_sg(struct request_queue *q, struct bio *bio,
struct scatterlist *sglist,
- struct scatterlist **sg)
+ struct scatterlist **sg, bool single_bio)
{
struct bio_vec bvec, bvprv = { NULL };
struct bvec_iter iter;
@@ -408,13 +408,39 @@ single_segment:
return 1;
}

- for_each_bio(bio)
+ if (!single_bio) {
+ for_each_bio(bio)
+ bio_for_each_segment(bvec, bio, iter)
+ __blk_segment_map_sg(q, &bvec, sglist, &bvprv,
+ sg, &nsegs, &cluster);
+ } else {
bio_for_each_segment(bvec, bio, iter)
- __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
- &nsegs, &cluster);
+ __blk_segment_map_sg(q, &bvec, sglist, &bvprv,
+ sg, &nsegs, &cluster);
+ }
+
+ return nsegs;
+}
+
+/*
+ * Map a bio to scatterlist, return number of sg entries setup. Caller must
+ * make sure sg can hold bio segments entries.
+ */
+int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
+ struct scatterlist *sglist)
+{
+ struct scatterlist *sg = NULL;
+ int nsegs = 0;
+
+ if (bio)
+ nsegs = __blk_bios_map_sg(q, bio, sglist, &sg, true);
+
+ if (sg)
+ sg_mark_end(sg);

return nsegs;
}
+EXPORT_SYMBOL(blk_bio_map_sg);

/*
* map a request to scatterlist, return number of sg entries setup. Caller
@@ -427,7 +453,7 @@ int blk_rq_map_sg(struct request_queue *q, struct request *rq,
int nsegs = 0;

if (rq->bio)
- nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg);
+ nsegs = __blk_bios_map_sg(q, rq->bio, sglist, &sg, false);

if (unlikely(rq->cmd_flags & REQ_COPY_USER) &&
(blk_rq_bytes(rq) & q->dma_pad_mask)) {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1fd8fdf..5868062 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1013,6 +1013,8 @@ extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fu
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);

--
1.7.9.5