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

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  [RFC 1/3] block: Introduce blk_bio_map_sg() to map one bio Baolin Wang <baolin.wang@linaro.org> - 2016-05-25 08:20 +0200
    Re: [RFC 1/3] block: Introduce blk_bio_map_sg() to map one bio Ming Lei <ming.lei@canonical.com> - 2016-05-25 11:00 +0200
      Re: [RFC 1/3] block: Introduce blk_bio_map_sg() to map one bio Baolin Wang <baolin.wang@linaro.org> - 2016-05-25 11:10 +0200

#1406659 — [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@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 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

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#1406759

On Wed, May 25, 2016 at 2:12 PM, Baolin Wang <baolin.wang@linaro.org> wrote:
> 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@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 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);

You can use __blk_bios_map_sg() to implement blk_bio_map_sg(),
then code duplication may be avoided.

> +
> +/*
>   * 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
>

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#1406763

On 25 May 2016 at 16:52, Ming Lei <ming.lei@canonical.com> wrote:
>>  /*
>> + * 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);
>
> You can use __blk_bios_map_sg() to implement blk_bio_map_sg(),
> then code duplication may be avoided.

OK. I'll re-factor the code to map one bio.

>
>> +
>> +/*
>>   * 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
>>



-- 
Baolin.wang
Best Regards

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