block: add a bi_error field to struct bio

Currently we have two different ways to signal an I/O error on a BIO:

 (1) by clearing the BIO_UPTODATE flag
 (2) by returning a Linux errno value to the bi_end_io callback

The first one has the drawback of only communicating a single possible
error (-EIO), and the second one has the drawback of not beeing persistent
when bios are queued up, and are not passed along from child to parent
bio in the ever more popular chaining scenario.  Having both mechanisms
available has the additional drawback of utterly confusing driver authors
and introducing bugs where various I/O submitters only deal with one of
them, and the others have to add boilerplate code to deal with both kinds
of error returns.

So add a new bi_error field to store an errno value directly in struct
bio and remove the existing mechanisms to clean all this up.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 11 insertions, 12 deletions

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index fbe7c104531c..8f2ca18c71f4 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5741,23 +5741,23 @@ int btrfs_rmap_block(struct btrfs_mapping_tree *map_tree,
 	return 0;
 }
 
-static inline void btrfs_end_bbio(struct btrfs_bio *bbio, struct bio *bio, int err)
+static inline void btrfs_end_bbio(struct btrfs_bio *bbio, struct bio *bio)
 {
 	bio->bi_private = bbio->private;
 	bio->bi_end_io = bbio->end_io;
-	bio_endio(bio, err);
+	bio_endio(bio);
 
 	btrfs_put_bbio(bbio);
 }
 
-static void btrfs_end_bio(struct bio *bio, int err)
+static void btrfs_end_bio(struct bio *bio)
 {
 	struct btrfs_bio *bbio = bio->bi_private;
 	int is_orig_bio = 0;
 
-	if (err) {
+	if (bio->bi_error) {
 		atomic_inc(&bbio->error);
-		if (err == -EIO || err == -EREMOTEIO) {
+		if (bio->bi_error == -EIO || bio->bi_error == -EREMOTEIO) {
 			unsigned int stripe_index =
 				btrfs_io_bio(bio)->stripe_index;
 			struct btrfs_device *dev;
@@ -5795,17 +5795,16 @@ static void btrfs_end_bio(struct bio *bio, int err)
 		 * beyond the tolerance of the btrfs bio
 		 */
 		if (atomic_read(&bbio->error) > bbio->max_errors) {
-			err = -EIO;
+			bio->bi_error = -EIO;
 		} else {
 			/*
 			 * this bio is actually up to date, we didn't
 			 * go over the max number of errors
 			 */
-			set_bit(BIO_UPTODATE, &bio->bi_flags);
-			err = 0;
+			bio->bi_error = 0;
 		}
 
-		btrfs_end_bbio(bbio, bio, err);
+		btrfs_end_bbio(bbio, bio);
 	} else if (!is_orig_bio) {
 		bio_put(bio);
 	}
@@ -5826,7 +5825,7 @@ static noinline void btrfs_schedule_bio(struct btrfs_root *root,
 	struct btrfs_pending_bios *pending_bios;
 
 	if (device->missing || !device->bdev) {
-		bio_endio(bio, -EIO);
+		bio_io_error(bio);
 		return;
 	}
 
@@ -5973,8 +5972,8 @@ static void bbio_error(struct btrfs_bio *bbio, struct bio *bio, u64 logical)
 
 		btrfs_io_bio(bio)->mirror_num = bbio->mirror_num;
 		bio->bi_iter.bi_sector = logical >> 9;
-
-		btrfs_end_bbio(bbio, bio, -EIO);
+		bio->bi_error = -EIO;
+		btrfs_end_bbio(bbio, bio);
 	}
 }