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>

2 files changed, 7 insertions, 15 deletions

diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index 2f30ca91e4fa..b2066fb5b10f 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -227,27 +227,23 @@ static void hib_init_batch(struct hib_bio_batch *hb)
 	hb->error = 0;
 }
 
-static void hib_end_io(struct bio *bio, int error)
+static void hib_end_io(struct bio *bio)
 {
 	struct hib_bio_batch *hb = bio->bi_private;
-	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct page *page = bio->bi_io_vec[0].bv_page;
 
-	if (!uptodate || error) {
+	if (bio->bi_error) {
 		printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
 				imajor(bio->bi_bdev->bd_inode),
 				iminor(bio->bi_bdev->bd_inode),
 				(unsigned long long)bio->bi_iter.bi_sector);
-
-		if (!error)
-			error = -EIO;
 	}
 
 	if (bio_data_dir(bio) == WRITE)
 		put_page(page);
 
-	if (error && !hb->error)
-		hb->error = error;
+	if (bio->bi_error && !hb->error)
+		hb->error = bio->bi_error;
 	if (atomic_dec_and_test(&hb->count))
 		wake_up(&hb->wait);
 
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index b3e6b39b6cf9..90e72a0c3047 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -778,9 +778,6 @@ static void blk_add_trace_bio(struct request_queue *q, struct bio *bio,
 	if (likely(!bt))
 		return;
 
-	if (!error && !bio_flagged(bio, BIO_UPTODATE))
-		error = EIO;
-
 	__blk_add_trace(bt, bio->bi_iter.bi_sector, bio->bi_iter.bi_size,
 			bio->bi_rw, what, error, 0, NULL);
 }
@@ -887,8 +884,7 @@ static void blk_add_trace_split(void *ignore,
 
 		__blk_add_trace(bt, bio->bi_iter.bi_sector,
 				bio->bi_iter.bi_size, bio->bi_rw, BLK_TA_SPLIT,
-				!bio_flagged(bio, BIO_UPTODATE),
-				sizeof(rpdu), &rpdu);
+				bio->bi_error, sizeof(rpdu), &rpdu);
 	}
 }
 
@@ -920,8 +916,8 @@ static void blk_add_trace_bio_remap(void *ignore,
 	r.sector_from = cpu_to_be64(from);
 
 	__blk_add_trace(bt, bio->bi_iter.bi_sector, bio->bi_iter.bi_size,
-			bio->bi_rw, BLK_TA_REMAP,
-			!bio_flagged(bio, BIO_UPTODATE), sizeof(r), &r);
+			bio->bi_rw, BLK_TA_REMAP, bio->bi_error,
+			sizeof(r), &r);
 }
 
 /**