block: remove bio_rewind_iter()

It is pointed that bio_rewind_iter() is one very bad API[1]:

1) bio size may not be restored after rewinding

2) it causes some bogus change, such as 5151842b9d8732 (block: reset
bi_iter.bi_done after splitting bio)

3) rewinding really makes things complicated wrt. bio splitting

4) unnecessary updating of .bi_done in fast path

[1] https://marc.info/?t=153549924200005&r=1&w=2

So this patch takes Kent's suggestion to restore one bio into its original
state via saving bio iterator(struct bvec_iter) in bio_integrity_prep(),
given now bio_rewind_iter() is only used by bio integrity code.

Cc: Dmitry Monakhov <[email protected]>
Cc: Hannes Reinecke <[email protected]>
Suggested-by: Kent Overstreet <[email protected]>
Acked-by: Kent Overstreet <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

2 files changed, 4 insertions, 21 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 51371740d2a8..14b4fa266357 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -170,27 +170,11 @@ static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 {
 	iter->bi_sector += bytes >> 9;
 
-	if (bio_no_advance_iter(bio)) {
+	if (bio_no_advance_iter(bio))
 		iter->bi_size -= bytes;
-		iter->bi_done += bytes;
-	} else {
+	else
 		bvec_iter_advance(bio->bi_io_vec, iter, bytes);
 		/* TODO: It is reasonable to complete bio with error here. */
-	}
-}
-
-static inline bool bio_rewind_iter(struct bio *bio, struct bvec_iter *iter,
-		unsigned int bytes)
-{
-	iter->bi_sector -= bytes >> 9;
-
-	if (bio_no_advance_iter(bio)) {
-		iter->bi_size += bytes;
-		iter->bi_done -= bytes;
-		return true;
-	}
-
-	return bvec_iter_rewind(bio->bi_io_vec, iter, bytes);
 }
 
 #define __bio_for_each_segment(bvl, bio, iter, start)			\
@@ -353,6 +337,8 @@ struct bio_integrity_payload {
 	unsigned short		bip_max_vcnt;	/* integrity bio_vec slots */
 	unsigned short		bip_flags;	/* control flags */
 
+	struct bvec_iter	bio_iter;	/* for rewinding parent bio */
+
 	struct work_struct	bip_work;	/* I/O completion */
 
 	struct bio_vec		*bip_vec;
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index fe7a22dd133b..02c73c6aa805 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -40,8 +40,6 @@ struct bvec_iter {
 
 	unsigned int		bi_idx;		/* current index into bvl_vec */
 
-	unsigned int            bi_done;	/* number of bytes completed */
-
 	unsigned int            bi_bvec_done;	/* number of bytes completed in
 						   current bvec */
 };
@@ -85,7 +83,6 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 		bytes -= len;
 		iter->bi_size -= len;
 		iter->bi_bvec_done += len;
-		iter->bi_done += len;
 
 		if (iter->bi_bvec_done == __bvec_iter_bvec(bv, *iter)->bv_len) {
 			iter->bi_bvec_done = 0;