linux-kernel - [RFC 1/3] block: Introduce blk_bio_map

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Message-Id: <abe693fad3abb0adfc0cf9ca5b3d287fdb0f2d5b.1464144791.git.baolin.wang@linaro.org>
Date:	Wed, 25 May 2016 14:12:29 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	axboe@...nel.dk, agk@...hat.com, snitzer@...hat.com,
	dm-devel@...hat.com, herbert@...dor.apana.org.au,
	davem@...emloft.net
Cc:	ebiggers3@...il.com, js1304@...il.com, tadeusz.struk@...el.com,
	smueller@...onox.de, standby24x7@...il.com, shli@...nel.org,
	dan.j.williams@...el.com, martin.petersen@...cle.com,
	sagig@...lanox.com, kent.overstreet@...il.com,
	keith.busch@...el.com, tj@...nel.org, ming.lei@...onical.com,
	broonie@...nel.org, arnd@...db.de, linux-crypto@...r.kernel.org,
	linux-block@...r.kernel.org, linux-raid@...r.kernel.org,
	linux-kernel@...r.kernel.org, baolin.wang@...aro.org
Subject: [RFC 1/3] block: Introduce blk_bio_map_sg() to map one bio

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.

Signed-off-by: Baolin Wang <baolin.wang@...aro.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 2613531..9b92af4 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -417,6 +417,51 @@ 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 1fd8fdf..e5de4f8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1013,6 +1013,9 @@ 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,
+			  struct scatterlist **sg);
 extern void blk_dump_rq_flags(struct request *, char *);
 extern long nr_blockdev_pages(void);
 
-- 
1.7.9.5