Add mddev_bio_split_at_reshape_offset() so personalities can share
reshape-offset bio splitting instead of open-coding the same helper in
multiple places.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
---
 drivers/md/md.c | 39 +++++++++++++++++++++++++++++++++++++++
 drivers/md/md.h |  4 ++++
 2 files changed, 43 insertions(+)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 5b001e3e4cec..d222e365141b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -9301,6 +9301,45 @@ void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
 }
 EXPORT_SYMBOL_GPL(md_submit_discard_bio);
 
+struct bio *mddev_bio_split_at_reshape_offset(struct mddev *mddev,
+					      struct bio *bio,
+					      unsigned int *max_sectors,
+					      struct bio_set *bs)
+{
+	sector_t boundary;
+	sector_t start;
+	sector_t end;
+	unsigned int split_sectors;
+
+	split_sectors = bio_sectors(bio);
+	if (max_sectors && *max_sectors && *max_sectors < split_sectors)
+		split_sectors = *max_sectors;
+
+	if (!test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
+		goto split;
+
+	boundary = mddev->reshape_position;
+	start = bio->bi_iter.bi_sector;
+	end = bio_end_sector(bio);
+	if (start >= boundary || end <= boundary)
+		goto split;
+
+	if (boundary - start < split_sectors)
+		split_sectors = boundary - start;
+
+split:
+	if (max_sectors)
+		*max_sectors = split_sectors;
+	if (split_sectors < bio_sectors(bio)) {
+		bio = bio_submit_split_bioset(bio, split_sectors, bs);
+		if (bio)
+			bio->bi_opf |= REQ_NOMERGE;
+	}
+
+	return bio;
+}
+EXPORT_SYMBOL_GPL(mddev_bio_split_at_reshape_offset);
+
 static void md_bitmap_prepare_range(struct mddev *mddev, sector_t *offset,
 				    unsigned long *sectors)
 {
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 82a36bdaeaaa..7247eeca5aa4 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -920,6 +920,10 @@ extern void md_error(struct mddev *mddev, struct md_rdev *rdev);
 extern void md_finish_reshape(struct mddev *mddev);
 void md_submit_discard_bio(struct mddev *mddev, struct md_rdev *rdev,
 			struct bio *bio, sector_t start, sector_t size);
+struct bio *mddev_bio_split_at_reshape_offset(struct mddev *mddev,
+					      struct bio *bio,
+					      unsigned int *max_sectors,
+					      struct bio_set *bs);
 void md_account_bio(struct mddev *mddev, struct bio **bio);
 void md_free_cloned_bio(struct bio *bio);
 
-- 
2.51.0