[PATCH V2 2/3] block: don't initialize bi_vcnt for cloned bio in bio_iov_bvec_set()

[Ming Lei <ming.lei@redhat.com>]

bio_iov_bvec_set() creates a cloned bio that borrows a bvec array from
an iov_iter. For cloned bios, bi_vcnt is meaningless because iteration
is controlled entirely by bi_iter (bi_idx, bi_size, bi_bvec_done), not
by bi_vcnt. Remove the incorrect bi_vcnt assignment.

Explicitly initialize bi_iter.bi_idx to 0 to ensure iteration starts
at the first bvec. While bi_idx is typically already zero from bio
initialization, making this explicit improves clarity and correctness.

This change also avoids accessing iter->nr_segs, which is an iov_iter
implementation detail that block code should not depend on.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/bio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 0e936288034e..2359c0723b88 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1165,8 +1165,8 @@ void bio_iov_bvec_set(struct bio *bio, const struct iov_iter *iter)
 {
 	WARN_ON_ONCE(bio->bi_max_vecs);
 
-	bio->bi_vcnt = iter->nr_segs;
 	bio->bi_io_vec = (struct bio_vec *)iter->bvec;
+	bio->bi_iter.bi_idx = 0;
 	bio->bi_iter.bi_bvec_done = iter->iov_offset;
 	bio->bi_iter.bi_size = iov_iter_count(iter);
 	bio_set_flag(bio, BIO_CLONED);
-- 
2.47.0