Re: [PATCH 01/17] block: export bio_split_rw

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On 2022/9/1 15:42, Christoph Hellwig wrote:
bio_split_rw can be used by file systems to split and incoming write
bio into multiple bios fitting the hardware limit for use as ZONE_APPEND
bios.  Export it for initial use in btrfs.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
  block/blk-merge.c   | 3 ++-
  include/linux/bio.h | 4 ++++
  2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/block/blk-merge.c b/block/blk-merge.c
index ff04e9290715a..e68295462977b 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -267,7 +267,7 @@ static bool bvec_split_segs(struct queue_limits *lim, const struct bio_vec *bv,
   * responsible for ensuring that @bs is only destroyed after processing of the
   * split bio has finished.
   */
-static struct bio *bio_split_rw(struct bio *bio, struct queue_limits *lim,
+struct bio *bio_split_rw(struct bio *bio, struct queue_limits *lim,

I found the queue_limits structure pretty scary, while we only have very
limited members used in this case:

- lim->virt_boundary_mask
  Used in bvec_gap_to_prev()

- lim->max_segments

- lim->seg_boundary_mask
- lim->max_segment_size
  Used in bvec_split_segs()

- lim->logical_block_size

Not familiar with block layer, thus I'm wondering do btrfs really need a
full queue_limits structure to call bio_split_rw().

Or can we have a simplified wrapper?

IIRC inside btrfs we only need two cases for bio split:

- Split for stripe boundary

- Split for OE/zoned boundary

Thanks,
Qu

  		unsigned *segs, struct bio_set *bs, unsigned max_bytes)
  {
  	struct bio_vec bv, bvprv, *bvprvp = NULL;
@@ -317,6 +317,7 @@ static struct bio *bio_split_rw(struct bio *bio, struct queue_limits *lim,
  	bio_clear_polled(bio);
  	return bio_split(bio, bytes >> SECTOR_SHIFT, GFP_NOIO, bs);
  }
+EXPORT_SYMBOL_GPL(bio_split_rw);

  /**
   * __bio_split_to_limits - split a bio to fit the queue limits
diff --git a/include/linux/bio.h b/include/linux/bio.h
index ca22b06700a94..46890f8235401 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -12,6 +12,8 @@

  #define BIO_MAX_VECS		256U

+struct queue_limits;
+
  static inline unsigned int bio_max_segs(unsigned int nr_segs)
  {
  	return min(nr_segs, BIO_MAX_VECS);
@@ -375,6 +377,8 @@ static inline void bip_set_seed(struct bio_integrity_payload *bip,
  void bio_trim(struct bio *bio, sector_t offset, sector_t size);
  extern struct bio *bio_split(struct bio *bio, int sectors,
  			     gfp_t gfp, struct bio_set *bs);
+struct bio *bio_split_rw(struct bio *bio, struct queue_limits *lim,
+		unsigned *segs, struct bio_set *bs, unsigned max_bytes);

  /**
   * bio_next_split - get next @sectors from a bio, splitting if necessary




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