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, 19 insertions, 16 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a9aadb2..a8c0de8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -703,7 +703,7 @@ static int btree_io_failed_hook(struct page *page, int failed_mirror)
 	return -EIO;	/* we fixed nothing */
 }
 
-static void end_workqueue_bio(struct bio *bio, int err)
+static void end_workqueue_bio(struct bio *bio)
 {
 	struct btrfs_end_io_wq *end_io_wq = bio->bi_private;
 	struct btrfs_fs_info *fs_info;
@@ -711,7 +711,7 @@ static void end_workqueue_bio(struct bio *bio, int err)
 	btrfs_work_func_t func;
 
 	fs_info = end_io_wq->info;
-	end_io_wq->error = err;
+	end_io_wq->error = bio->bi_error;
 
 	if (bio->bi_rw & REQ_WRITE) {
 		if (end_io_wq->metadata == BTRFS_WQ_ENDIO_METADATA) {
@@ -808,7 +808,8 @@ static void run_one_async_done(struct btrfs_work *work)
 
 	/* If an error occured we just want to clean up the bio and move on */
 	if (async->error) {
-		bio_endio(async->bio, async->error);
+		async->bio->bi_error = async->error;
+		bio_endio(async->bio);
 		return;
 	}
 
@@ -908,8 +909,10 @@ static int __btree_submit_bio_done(struct inode *inode, int rw, struct bio *bio,
 	 * submission context.  Just jump into btrfs_map_bio
 	 */
 	ret = btrfs_map_bio(BTRFS_I(inode)->root, rw, bio, mirror_num, 1);
-	if (ret)
-		bio_endio(bio, ret);
+	if (ret) {
+		bio->bi_error = ret;
+		bio_endio(bio);
+	}
 	return ret;
 }
 
@@ -960,10 +963,13 @@ static int btree_submit_bio_hook(struct inode *inode, int rw, struct bio *bio,
 					  __btree_submit_bio_done);
 	}
 
-	if (ret) {
+	if (ret)
+		goto out_w_error;
+	return 0;
+
 out_w_error:
-		bio_endio(bio, ret);
-	}
+	bio->bi_error = ret;
+	bio_endio(bio);
 	return ret;
 }
 
@@ -1735,16 +1741,15 @@ static void end_workqueue_fn(struct btrfs_work *work)
 {
 	struct bio *bio;
 	struct btrfs_end_io_wq *end_io_wq;
-	int error;
 
 	end_io_wq = container_of(work, struct btrfs_end_io_wq, work);
 	bio = end_io_wq->bio;
 
-	error = end_io_wq->error;
+	bio->bi_error = end_io_wq->error;
 	bio->bi_private = end_io_wq->private;
 	bio->bi_end_io = end_io_wq->end_io;
 	kmem_cache_free(btrfs_end_io_wq_cache, end_io_wq);
-	bio_endio(bio, error);
+	bio_endio(bio);
 }
 
 static int cleaner_kthread(void *arg)
@@ -3323,10 +3328,8 @@ static int write_dev_supers(struct btrfs_device *device,
  * endio for the write_dev_flush, this will wake anyone waiting
  * for the barrier when it is done
  */
-static void btrfs_end_empty_barrier(struct bio *bio, int err)
+static void btrfs_end_empty_barrier(struct bio *bio)
 {
-	if (err)
-		clear_bit(BIO_UPTODATE, &bio->bi_flags);
 	if (bio->bi_private)
 		complete(bio->bi_private);
 	bio_put(bio);
@@ -3354,8 +3357,8 @@ static int write_dev_flush(struct btrfs_device *device, int wait)
 
 		wait_for_completion(&device->flush_wait);
 
-		if (!bio_flagged(bio, BIO_UPTODATE)) {
-			ret = -EIO;
+		if (bio->bi_error) {
+			ret = bio->bi_error;
 			btrfs_dev_stat_inc_and_print(device,
 				BTRFS_DEV_STAT_FLUSH_ERRS);
 		}