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, 4 insertions, 7 deletions

diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
index ad1b049ae2ab..e9d17488d5e3 100644
--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -146,16 +146,16 @@ static void put_io_block(struct log_writes_c *lc)
         }
 }
 
-static void log_end_io(struct bio *bio, int err)
+static void log_end_io(struct bio *bio)
 {
         struct log_writes_c *lc = bio->bi_private;
         struct bio_vec *bvec;
         int i;
 
-        if (err) {
+        if (bio->bi_error) {
                 unsigned long flags;
 
-                DMERR("Error writing log block, error=%d", err);
+                DMERR("Error writing log block, error=%d", bio->bi_error);
                 spin_lock_irqsave(&lc->blocks_lock, flags);
                 lc->logging_enabled = false;
                 spin_unlock_irqrestore(&lc->blocks_lock, flags);
@@ -205,7 +205,6 @@ static int write_metadata(struct log_writes_c *lc, void *entry,
         bio->bi_bdev = lc->logdev->bdev;
         bio->bi_end_io = log_end_io;
         bio->bi_private = lc;
-        set_bit(BIO_UPTODATE, &bio->bi_flags);
 
         page = alloc_page(GFP_KERNEL);
         if (!page) {
@@ -270,7 +269,6 @@ static int log_one_block(struct log_writes_c *lc,
         bio->bi_bdev = lc->logdev->bdev;
         bio->bi_end_io = log_end_io;
         bio->bi_private = lc;
-        set_bit(BIO_UPTODATE, &bio->bi_flags);
 
         for (i = 0; i < block->vec_cnt; i++) {
                 /*
@@ -292,7 +290,6 @@ static int log_one_block(struct log_writes_c *lc,
                         bio->bi_bdev = lc->logdev->bdev;
                         bio->bi_end_io = log_end_io;
                         bio->bi_private = lc;
-                        set_bit(BIO_UPTODATE, &bio->bi_flags);
 
                         ret = bio_add_page(bio, block->vecs[i].bv_page,
                                            block->vecs[i].bv_len, 0);
@@ -606,7 +603,7 @@ static int log_writes_map(struct dm_target *ti, struct bio *bio)
                 WARN_ON(flush_bio || fua_bio);
                 if (lc->device_supports_discard)
                         goto map_bio;
-                bio_endio(bio, 0);
+                bio_endio(bio);
                 return DM_MAPIO_SUBMITTED;
         }