[RFC 03/12] bio: add bio_set_errno

[Andreas Gruenbacher <agruenba@redhat.com>]

Add a bio_set_errno(bio, errno) helper that sets bio->bi_status to
errno_to_blk_status(errno) if errno != 0.  Replace instances of this
pattern in the code with a call to the new helper.

The WRITE_ONCE() in bio_set_errno() ensures that the compiler won't
reorder things in a weird way, but it isn't needed to prevent tearing
because a single-byte field like bi_status cannot tear.

Created with Coccinelle using the following semantic patch:

@@
struct bio *bio;
expression errno;
@@
- if (errno)
-	bio->bi_status = errno_to_blk_status(errno);
+ bio_set_errno(bio, errno);

@@
struct bio *bio;
expression errno;
@@
- if (unlikely(errno))
-	bio->bi_status = errno_to_blk_status(errno);
+ bio_set_errno(bio, errno);

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 drivers/block/drbd/drbd_req.c | 3 +--
 drivers/nvdimm/pmem.c         | 3 +--
 include/linux/bio.h           | 8 ++++++++
 3 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index d15826f6ee81..bd4bc882cc5a 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -176,8 +176,7 @@ void start_new_tl_epoch(struct drbd_connection *connection)
 void complete_master_bio(struct drbd_device *device,
 		struct bio_and_error *m)
 {
-	if (unlikely(m->error))
-		m->bio->bi_status = errno_to_blk_status(m->error);
+	bio_set_errno(m->bio, m->error);
 	bio_endio(m->bio);
 	dec_ap_bio(device);
 }
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 05785ff21a8b..a2f8b5a85326 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -232,8 +232,7 @@ static void pmem_submit_bio(struct bio *bio)
 	if (bio->bi_opf & REQ_FUA)
 		ret = nvdimm_flush(nd_region, bio);
 
-	if (ret)
-		bio->bi_status = errno_to_blk_status(ret);
+	bio_set_errno(bio, ret);
 
 	bio_endio(bio);
 }
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 16c1c85613b7..38ebf03036cb 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -389,6 +389,14 @@ static inline void bio_wouldblock_error(struct bio *bio)
 	bio_endio(bio);
 }
 
+blk_status_t errno_to_blk_status(int errno);
+
+static inline void bio_set_errno(struct bio *bio, int errno)
+{
+	if (errno)
+		WRITE_ONCE(bio->bi_status, errno_to_blk_status(errno));
+}
+
 /*
  * Calculate number of bvec segments that should be allocated to fit data
  * pointed by @iter. If @iter is backed by bvec it's going to be reused
-- 
2.51.0