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, 14 insertions, 10 deletions

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index ce62324c78e7..302266ec2cdb 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -152,7 +152,7 @@ fail:
  * The compressed pages are freed here, and it must be run
  * in process context
  */
-static void end_compressed_bio_read(struct bio *bio, int err)
+static void end_compressed_bio_read(struct bio *bio)
 {
         struct compressed_bio *cb = bio->bi_private;
         struct inode *inode;
@@ -160,7 +160,7 @@ static void end_compressed_bio_read(struct bio *bio, int err)
         unsigned long index;
         int ret;
 
-        if (err)
+        if (bio->bi_error)
                 cb->errors = 1;
 
         /* if there are more bios still pending for this compressed
@@ -210,7 +210,7 @@ csum_failed:
                 bio_for_each_segment_all(bvec, cb->orig_bio, i)
                         SetPageChecked(bvec->bv_page);
 
-                bio_endio(cb->orig_bio, 0);
+                bio_endio(cb->orig_bio);
         }
 
         /* finally free the cb struct */
@@ -266,7 +266,7 @@ static noinline void end_compressed_writeback(struct inode *inode,
  * This also calls the writeback end hooks for the file pages so that
  * metadata and checksums can be updated in the file.
  */
-static void end_compressed_bio_write(struct bio *bio, int err)
+static void end_compressed_bio_write(struct bio *bio)
 {
         struct extent_io_tree *tree;
         struct compressed_bio *cb = bio->bi_private;
@@ -274,7 +274,7 @@ static void end_compressed_bio_write(struct bio *bio, int err)
         struct page *page;
         unsigned long index;
 
-        if (err)
+        if (bio->bi_error)
                 cb->errors = 1;
 
         /* if there are more bios still pending for this compressed
@@ -293,7 +293,7 @@ static void end_compressed_bio_write(struct bio *bio, int err)
                                          cb->start,
                                          cb->start + cb->len - 1,
                                          NULL,
-                                         err ? 0 : 1);
+                                         bio->bi_error ? 0 : 1);
         cb->compressed_pages[0]->mapping = NULL;
 
         end_compressed_writeback(inode, cb);
@@ -697,8 +697,10 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
                         ret = btrfs_map_bio(root, READ, comp_bio,
                                             mirror_num, 0);
-                        if (ret)
-                                bio_endio(comp_bio, ret);
+                        if (ret) {
+                                bio->bi_error = ret;
+                                bio_endio(comp_bio);
+                        }
 
                         bio_put(comp_bio);
 
@@ -724,8 +726,10 @@ int btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
         }
 
         ret = btrfs_map_bio(root, READ, comp_bio, mirror_num, 0);
-        if (ret)
-                bio_endio(comp_bio, ret);
+        if (ret) {
+                bio->bi_error = ret;
+                bio_endio(comp_bio);
+        }
 
         bio_put(comp_bio);
         return 0;