In dm-crypt, it need to map one bio to scatterlist for improving the
encryption efficiency. Thus this patch introduces the blk_bio_map_sg()
function to map one bio with scatterlists.
Signed-off-by: Baolin Wang <baolin.w...@linaro.org>
---
block/blk-merge.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 3 +++
2 files changed, 48 insertions(+)
diff --git a/block/blk-merge.c b/block/blk-merge.c
index de5716d8..281b9e5 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -374,6 +374,51 @@ single_segment:
}
/*
+ * map a bio to scatterlist, return number of sg entries setup.
+ */
+int blk_bio_map_sg(struct request_queue *q, struct bio *bio,
+ struct scatterlist *sglist,
+ struct scatterlist **sg)
+{
+ struct bio_vec bvec, bvprv = { NULL };
+ struct bvec_iter iter;
+ int nsegs, cluster;
+
+ nsegs = 0;
+ cluster = blk_queue_cluster(q);
+
+ if (bio->bi_rw & REQ_DISCARD) {
+ /*
+ * This is a hack - drivers should be neither modifying the
+ * biovec, nor relying on bi_vcnt - but because of
+ * blk_add_request_payload(), a discard bio may or may not have
+ * a payload we need to set up here (thank you Christoph) and
+ * bi_vcnt is really the only way of telling if we need to.
+ */
+
+ if (bio->bi_vcnt)
+ goto single_segment;
+
+ return 0;
+ }
+
+ if (bio->bi_rw & REQ_WRITE_SAME) {
+single_segment:
+ *sg = sglist;
+ bvec = bio_iovec(bio);
+ sg_set_page(*sg, bvec.bv_page, bvec.bv_len, bvec.bv_offset);
+ return 1;
+ }
+
+ bio_for_each_segment(bvec, bio, iter)
+ __blk_segment_map_sg(q, &bvec, sglist, &bvprv, sg,
+ &nsegs, &cluster);
+
+ return nsegs;
+}
+EXPORT_SYMBOL(blk_bio_map_sg);
+
+/*
* map a request to scatterlist, return number of sg entries setup. Caller
* must make sure sg can hold rq->nr_phys_segments entries
*/
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 3fe27f8..3ca90ac 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1004,6 +1004,9 @@ 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,
+ struct scatterlist **sg);
extern void blk_dump_rq_flags(struct request *, char *);
extern long nr_blockdev_pages(void);
--
1.7.9.5
--
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