Re: No way to break bio_for_each_segment_all() macro?

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

On Sat, Apr 06, 2019 at 09:53:07AM +0800, Qu Wenruo wrote:
> Hi,
> 
> I'm looking into a strange behavior that we can't break
> bio_for_each_segment_all() after commit 6dc4f100c175 ("block: allow
> bio_for_each_segment_all() to iterate over multi-page bvec").
> 
> It's screwing up all bio_for_each_segment_all() call with error out branch.
> 

Please test the following patch:

--

diff --git a/include/linux/bio.h b/include/linux/bio.h
index bb6090aa165d..7bd7e64e02f8 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -120,19 +120,15 @@ static inline bool bio_full(struct bio *bio)
 	return bio->bi_vcnt >= bio->bi_max_vecs;
 }
 
-#define mp_bvec_for_each_segment(bv, bvl, i, iter_all)			\
-	for (bv = bvec_init_iter_all(&iter_all);			\
-		(iter_all.done < (bvl)->bv_len) &&			\
-		(mp_bvec_next_segment((bvl), &iter_all), 1);		\
-		iter_all.done += bv->bv_len, i += 1)
-
 /*
  * drivers should _never_ use the all version - the bio may have been split
  * before it got to the driver and the driver won't own all of it
  */
-#define bio_for_each_segment_all(bvl, bio, i, iter_all)		\
-	for (i = 0, iter_all.idx = 0; iter_all.idx < (bio)->bi_vcnt; iter_all.idx++)	\
-		mp_bvec_for_each_segment(bvl, &((bio)->bi_io_vec[iter_all.idx]), i, iter_all)
+#define bio_for_each_segment_all(bvl, bio, i, iter_all)			\
+	for (i = 0, bvl = bvec_init_iter_all(&iter_all);		\
+		iter_all.idx < (bio)->bi_vcnt &&			\
+		(mp_bvec_advance(&((bio)->bi_io_vec[iter_all.idx]),	\
+				 &iter_all), 1); i++)
 
 static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
 				    unsigned bytes)
diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index f6275c4da13a..6e4996dfc847 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -48,7 +48,7 @@ struct bvec_iter {
 struct bvec_iter_all {
 	struct bio_vec	bv;
 	int		idx;
-	unsigned	done;
+	unsigned	bv_done;
 };
 
 static inline struct page *bvec_nth_page(struct page *page, int idx)
@@ -145,18 +145,18 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 
 static inline struct bio_vec *bvec_init_iter_all(struct bvec_iter_all *iter_all)
 {
-	iter_all->bv.bv_page = NULL;
-	iter_all->done = 0;
+	iter_all->bv_done = 0;
+	iter_all->idx = 0;
 
 	return &iter_all->bv;
 }
 
-static inline void mp_bvec_next_segment(const struct bio_vec *bvec,
-					struct bvec_iter_all *iter_all)
+static inline void mp_bvec_advance(const struct bio_vec *bvec,
+				   struct bvec_iter_all *iter_all)
 {
 	struct bio_vec *bv = &iter_all->bv;
 
-	if (bv->bv_page) {
+	if (iter_all->bv_done) {
 		bv->bv_page = nth_page(bv->bv_page, 1);
 		bv->bv_offset = 0;
 	} else {
@@ -164,7 +164,13 @@ static inline void mp_bvec_next_segment(const struct bio_vec *bvec,
 		bv->bv_offset = bvec->bv_offset;
 	}
 	bv->bv_len = min_t(unsigned int, PAGE_SIZE - bv->bv_offset,
-			   bvec->bv_len - iter_all->done);
+			   bvec->bv_len - iter_all->bv_done);
+	iter_all->bv_done += bv->bv_len;
+
+	if (iter_all->bv_done == bvec->bv_len) {
+		iter_all->idx++;
+		iter_all->bv_done = 0;
+	}
 }
 
 /*

Thanks,
Ming