From: Yu Kuai <yukuai3@huawei.com>

No functional changes are intended, some drivers like mdraid will split
bio by internal processing, prepare to unify bio split codes.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 block/blk-merge.c   | 60 +++++++++++++++++++++++++++++----------------
 include/linux/bio.h |  2 ++
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index 70d704615be5..c45d5e43e172 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -104,35 +104,49 @@ static unsigned int bio_allowed_max_sectors(const struct queue_limits *lim)
 	return round_down(UINT_MAX, lim->logical_block_size) >> SECTOR_SHIFT;
 }
 
-static struct bio *bio_submit_split(struct bio *bio, int split_sectors)
+/**
+ * bio_submit_split - Submit a bio, splitting it at a designated sector
+ * @bio:           the original bio to be submitted and split
+ * @split_sectors: the sector count (from the start of @bio) at which to split
+ * @bs:            the bio set used for allocating the new split bio
+ *
+ * The original bio is modified to contain the remaining sectors and submitted.
+ * The caller is responsible for submitting the returned bio.
+ *
+ * If succeed, the newly allocated bio representing the initial part will be
+ * returned, on failure NULL will be returned and original bio will fail.
+ */
+struct bio *bio_submit_split(struct bio *bio, int split_sectors,
+			     struct bio_set *bs)
 {
+	struct bio *split;
+
 	if (unlikely(split_sectors < 0))
 		goto error;
 
-	if (split_sectors) {
-		struct bio *split;
+	if (!split_sectors)
+		return bio;
 
-		split = bio_split(bio, split_sectors, GFP_NOIO,
-				&bio->bi_bdev->bd_disk->bio_split);
-		if (IS_ERR(split)) {
-			split_sectors = PTR_ERR(split);
-			goto error;
-		}
-		split->bi_opf |= REQ_NOMERGE;
-		blkcg_bio_issue_init(split);
-		bio_chain(split, bio);
-		trace_block_split(split, bio->bi_iter.bi_sector);
-		WARN_ON_ONCE(bio_zone_write_plugging(bio));
-		submit_bio_noacct(bio);
-		return split;
+	split = bio_split(bio, split_sectors, GFP_NOIO, bs);
+	if (IS_ERR(split)) {
+		split_sectors = PTR_ERR(split);
+		goto error;
 	}
 
-	return bio;
+	split->bi_opf |= REQ_NOMERGE;
+	blkcg_bio_issue_init(split);
+	bio_chain(split, bio);
+	trace_block_split(split, bio->bi_iter.bi_sector);
+	WARN_ON_ONCE(bio_zone_write_plugging(bio));
+	submit_bio_noacct(bio);
+	return split;
+
 error:
 	bio->bi_status = errno_to_blk_status(split_sectors);
 	bio_endio(bio);
 	return NULL;
 }
+EXPORT_SYMBOL_GPL(bio_submit_split);
 
 struct bio *bio_split_discard(struct bio *bio, const struct queue_limits *lim,
 		unsigned *nsegs)
@@ -167,7 +181,8 @@ struct bio *bio_split_discard(struct bio *bio, const struct queue_limits *lim,
 	if (split_sectors > tmp)
 		split_sectors -= tmp;
 
-	return bio_submit_split(bio, split_sectors);
+	return bio_submit_split(bio, split_sectors,
+				&bio->bi_bdev->bd_disk->bio_split);
 }
 
 static inline unsigned int blk_boundary_sectors(const struct queue_limits *lim,
@@ -357,7 +372,8 @@ struct bio *bio_split_rw(struct bio *bio, const struct queue_limits *lim,
 {
 	return bio_submit_split(bio,
 		bio_split_rw_at(bio, lim, nr_segs,
-			get_max_io_size(bio, lim) << SECTOR_SHIFT));
+			get_max_io_size(bio, lim) << SECTOR_SHIFT),
+			&bio->bi_bdev->bd_disk->bio_split);
 }
 
 /*
@@ -376,7 +392,8 @@ struct bio *bio_split_zone_append(struct bio *bio,
 			lim->max_zone_append_sectors << SECTOR_SHIFT);
 	if (WARN_ON_ONCE(split_sectors > 0))
 		split_sectors = -EINVAL;
-	return bio_submit_split(bio, split_sectors);
+	return bio_submit_split(bio, split_sectors,
+				&bio->bi_bdev->bd_disk->bio_split);
 }
 
 struct bio *bio_split_write_zeroes(struct bio *bio,
@@ -396,7 +413,8 @@ struct bio *bio_split_write_zeroes(struct bio *bio,
 		return bio;
 	if (bio_sectors(bio) <= max_sectors)
 		return bio;
-	return bio_submit_split(bio, max_sectors);
+	return bio_submit_split(bio, max_sectors,
+				&bio->bi_bdev->bd_disk->bio_split);
 }
 
 /**
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 46ffac5caab7..2233261be5e8 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -324,6 +324,8 @@ extern struct bio *bio_split(struct bio *bio, int sectors,
 			     gfp_t gfp, struct bio_set *bs);
 int bio_split_rw_at(struct bio *bio, const struct queue_limits *lim,
 		unsigned *segs, unsigned max_bytes);
+struct bio *bio_submit_split(struct bio *bio, int split_sectors,
+			     struct bio_set *bs);
 
 /**
  * bio_next_split - get next @sectors from a bio, splitting if necessary
-- 
2.39.2

On Mon, Aug 25, 2025 at 05:36:54PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> No functional changes are intended, some drivers like mdraid will split
> bio by internal processing, prepare to unify bio split codes.

Maybe name the exported helper bio_submit_split_bioset and keep
bio_submit_split() as a wrapper that passes the default split
bioset to keep the code a bit tidyer in blk-merge.c?

> +struct bio *bio_submit_split(struct bio *bio, int split_sectors,
> +			     struct bio_set *bs)
>  {
> +	struct bio *split;
> +
>  	if (unlikely(split_sectors < 0))
>  		goto error;
>  
> -	if (split_sectors) {
> -		struct bio *split;
> +	if (!split_sectors)
> +		return bio;
>  
> -		split = bio_split(bio, split_sectors, GFP_NOIO,
> -				&bio->bi_bdev->bd_disk->bio_split);
> -		if (IS_ERR(split)) {
> -			split_sectors = PTR_ERR(split);
> -			goto error;
> -		}
> -		split->bi_opf |= REQ_NOMERGE;
> -		blkcg_bio_issue_init(split);
> -		bio_chain(split, bio);
> -		trace_block_split(split, bio->bi_iter.bi_sector);
> -		WARN_ON_ONCE(bio_zone_write_plugging(bio));
> -		submit_bio_noacct(bio);

Maybe skip the reformatting which makes this much harder to read?
If you think it is useful it can be done in a separate patch.

Hi,

在 2025/08/25 18:53, Christoph Hellwig 写道:
> On Mon, Aug 25, 2025 at 05:36:54PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> No functional changes are intended, some drivers like mdraid will split
>> bio by internal processing, prepare to unify bio split codes.
> 
> Maybe name the exported helper bio_submit_split_bioset and keep
> bio_submit_split() as a wrapper that passes the default split
> bioset to keep the code a bit tidyer in blk-merge.c?
> 
Sure.

>> +struct bio *bio_submit_split(struct bio *bio, int split_sectors,
>> +			     struct bio_set *bs)
>>   {
>> +	struct bio *split;
>> +
>>   	if (unlikely(split_sectors < 0))
>>   		goto error;
>>   
>> -	if (split_sectors) {
>> -		struct bio *split;
>> +	if (!split_sectors)
>> +		return bio;
>>   
>> -		split = bio_split(bio, split_sectors, GFP_NOIO,
>> -				&bio->bi_bdev->bd_disk->bio_split);
>> -		if (IS_ERR(split)) {
>> -			split_sectors = PTR_ERR(split);
>> -			goto error;
>> -		}
>> -		split->bi_opf |= REQ_NOMERGE;
>> -		blkcg_bio_issue_init(split);
>> -		bio_chain(split, bio);
>> -		trace_block_split(split, bio->bi_iter.bi_sector);
>> -		WARN_ON_ONCE(bio_zone_write_plugging(bio));
>> -		submit_bio_noacct(bio);
> 
> Maybe skip the reformatting which makes this much harder to read?
> If you think it is useful it can be done in a separate patch.
> 
Please ignore this, I'll skip this.

Thanks for the review!
Kuai

> .
>