[PATCH] partial bio completion notification

Make bio->bi_end_io() take bytes_done and actual error as argument. This
enables partial completion of bio's, which is important for latency
reasons (bio can be huge, for slow media we want page-by-page
completions).

I think I got most of the bi_end_io() functions out there, but I might
have missed a few. For the record, if you don't care about partial
completions and just want to be notified when the entire bio completes,
add a

	if (bio->bi_size)
		return 1;

to the top of your bi_end_io(). It should return 0 on completion.
bio_endio() will decrement bio->bi_size appropriately, it's recommended
for people to go through that. Otherwise they will have to control
BIO_UPTODATE and bi_size decrement themselves, there's really no reason
to do that. I've deliberately avoided doing any functional changes to
any of the end_io functions, as I think that would only make the patch
more complex. It's simple right now, but this being i/o paths I prefer
(as usual) to be careful and take small steps. The mpage_end_io_read()
do-vecs-at-the-time change can come right after this, for instance.

1 files changed, 3 insertions, 3 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 8113ca45c3d2..e9a0d968d1e2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -51,7 +51,7 @@ struct bio_vec {
 };
 
 struct bio;
-typedef void (bio_end_io_t) (struct bio *);
+typedef int (bio_end_io_t) (struct bio *, unsigned int, int);
 typedef void (bio_destructor_t) (struct bio *);
 
 /*
@@ -161,7 +161,7 @@ struct bio {
 #define BIO_SEG_BOUNDARY(q, b1, b2) \
 	BIOVEC_SEG_BOUNDARY((q), __BVEC_END((b1)), __BVEC_START((b2)))
 
-#define bio_io_error(bio) bio_endio((bio), 0)
+#define bio_io_error(bio, bytes) bio_endio((bio), (bytes), -EIO)
 
 /*
  * drivers should not use the __ version unless they _really_ want to
@@ -194,7 +194,7 @@ struct bio {
 extern struct bio *bio_alloc(int, int);
 extern void bio_put(struct bio *);
 
-extern void bio_endio(struct bio *, int);
+extern int bio_endio(struct bio *, unsigned int, int);
 struct request_queue;
 extern inline int bio_phys_segments(struct request_queue *, struct bio *);
 extern inline int bio_hw_segments(struct request_queue *, struct bio *);