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, 8 insertions, 7 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 627ed0c593fb..7ef15b947b91 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -143,9 +143,7 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
                           unsigned int nbytes, int error)
 {
         if (error)
-                clear_bit(BIO_UPTODATE, &bio->bi_flags);
-        else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
-                error = -EIO;
+                bio->bi_error = error;
 
         if (unlikely(rq->cmd_flags & REQ_QUIET))
                 set_bit(BIO_QUIET, &bio->bi_flags);
@@ -154,7 +152,7 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
 
         /* don't actually finish bio if it's part of flush sequence */
         if (bio->bi_iter.bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ))
-                bio_endio(bio, error);
+                bio_endio(bio);
 }
 
 void blk_dump_rq_flags(struct request *rq, char *msg)
@@ -1620,7 +1618,8 @@ static void blk_queue_bio(struct request_queue *q, struct bio *bio)
         blk_queue_bounce(q, &bio);
 
         if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
-                bio_endio(bio, -EIO);
+                bio->bi_error = -EIO;
+                bio_endio(bio);
                 return;
         }
 
@@ -1673,7 +1672,8 @@ get_rq:
          */
         req = get_request(q, rw_flags, bio, GFP_NOIO);
         if (IS_ERR(req)) {
-                bio_endio(bio, PTR_ERR(req));   /* @q is dead */
+                bio->bi_error = PTR_ERR(req);
+                bio_endio(bio);
                 goto out_unlock;
         }
 
@@ -1896,7 +1896,8 @@ generic_make_request_checks(struct bio *bio)
         return true;
 
 end_io:
-        bio_endio(bio, err);
+        bio->bi_error = err;
+        bio_endio(bio);
         return false;
 }