Re: [PATCH] block: Simplify the bio cloning implementation

On 06/26/18 18:13, Ming Lei wrote:

On Tue, Jun 26, 2018 at 03:26:24PM -0700, Bart Van Assche wrote:

quoted

There is no good reason to use different code paths for different
request operations. Hence remove the switch/case statement from
bio_clone_bioset().

Signed-off-by: Bart Van Assche <redacted>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <redacted>
---
  block/bio.c | 15 ++-------------
  1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index f7e3d88bd0b6..4c27cc9ea55e 100644
--- a/block/bio.c
+++ b/block/bio.c

@@ -691,19 +691,8 @@ struct bio *bio_clone_bioset(struct bio *bio_src, gfp_t gfp_mask,
  	bio->bi_iter.bi_sector	= bio_src->bi_iter.bi_sector;
  	bio->bi_iter.bi_size	= bio_src->bi_iter.bi_size;
  
-	switch (bio_op(bio)) {
-	case REQ_OP_DISCARD:
-	case REQ_OP_SECURE_ERASE:
-	case REQ_OP_WRITE_ZEROES:
-		break;
-	case REQ_OP_WRITE_SAME:
-		bio->bi_io_vec[bio->bi_vcnt++] = bio_src->bi_io_vec[0];
-		break;
-	default:
-		bio_for_each_segment(bv, bio_src, iter)
-			bio->bi_io_vec[bio->bi_vcnt++] = bv;
-		break;
-	}
+	bio_for_each_segment(bv, bio_src, iter)
+		bio->bi_io_vec[bio->bi_vcnt++] = bv;

The above change may not be correct for WRITE_SAME, since
bio_src->bi_iter.bi_size should be the actual bytes to write by drive.

Since bio_for_each_segment() neither modifies bio_src->bi_iter nor 
bio->bi_iter, the above patch retains the value copied into 
bio->bi_iter.bi_size before bio_for_each_segment() was called. In other 
words, bio_src->bi_iter.bi_size is not modified and the resulting 
bio->bi_iter.bi_size should be identical with or without this patch.

Also Christoph has killed bio_clone_bioset() already, and I think that is
correct thing to do, see:

	https://marc.info/?l=linux-block&m=152938432207215&w=2

Anyway, I'm fine with using Christoph's approach and dropping this patch.

Bart.