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, 6 insertions, 7 deletions

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 745d2342651a..e1639c8c14d5 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -285,7 +285,7 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio);
 /*
  * Asynchronous IO callback. 
  */
-static void dio_bio_end_aio(struct bio *bio, int error)
+static void dio_bio_end_aio(struct bio *bio)
 {
         struct dio *dio = bio->bi_private;
         unsigned long remaining;
@@ -318,7 +318,7 @@ static void dio_bio_end_aio(struct bio *bio, int error)
  * During I/O bi_private points at the dio.  After I/O, bi_private is used to
  * implement a singly-linked list of completed BIOs, at dio->bio_list.
  */
-static void dio_bio_end_io(struct bio *bio, int error)
+static void dio_bio_end_io(struct bio *bio)
 {
         struct dio *dio = bio->bi_private;
         unsigned long flags;
@@ -345,9 +345,9 @@ void dio_end_io(struct bio *bio, int error)
         struct dio *dio = bio->bi_private;
 
         if (dio->is_async)
-                dio_bio_end_aio(bio, error);
+                dio_bio_end_aio(bio);
         else
-                dio_bio_end_io(bio, error);
+                dio_bio_end_io(bio);
 }
 EXPORT_SYMBOL_GPL(dio_end_io);
 
@@ -457,11 +457,10 @@ static struct bio *dio_await_one(struct dio *dio)
  */
 static int dio_bio_complete(struct dio *dio, struct bio *bio)
 {
-        const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
         struct bio_vec *bvec;
         unsigned i;
 
-        if (!uptodate)
+        if (bio->bi_error)
                 dio->io_error = -EIO;
 
         if (dio->is_async && dio->rw == READ) {
@@ -476,7 +475,7 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
                 }
                 bio_put(bio);
         }
-        return uptodate ? 0 : -EIO;
+        return bio->bi_error;
 }
 
 /*