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, 5 insertions, 7 deletions

diff --git a/mm/page_io.c b/mm/page_io.c
index 520baa4b..338ce68 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -43,12 +43,11 @@ static struct bio *get_swap_bio(gfp_t gfp_flags,
 	return bio;
 }
 
-void end_swap_bio_write(struct bio *bio, int err)
+void end_swap_bio_write(struct bio *bio)
 {
-	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct page *page = bio->bi_io_vec[0].bv_page;
 
-	if (!uptodate) {
+	if (bio->bi_error) {
 		SetPageError(page);
 		/*
 		 * We failed to write the page out to swap-space.
@@ -69,12 +68,11 @@ void end_swap_bio_write(struct bio *bio, int err)
 	bio_put(bio);
 }
 
-static void end_swap_bio_read(struct bio *bio, int err)
+static void end_swap_bio_read(struct bio *bio)
 {
-	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	struct page *page = bio->bi_io_vec[0].bv_page;
 
-	if (!uptodate) {
+	if (bio->bi_error) {
 		SetPageError(page);
 		ClearPageUptodate(page);
 		printk(KERN_ALERT "Read-error on swap-device (%u:%u:%Lu)\n",
@@ -254,7 +252,7 @@ static sector_t swap_page_sector(struct page *page)
 }
 
 int __swap_writepage(struct page *page, struct writeback_control *wbc,
-	void (*end_write_func)(struct bio *, int))
+		bio_end_io_t end_write_func)
 {
 	struct bio *bio;
 	int ret, rw = WRITE;