block: Generic bio chaining

This adds a generic mechanism for chaining bio completions. This is
going to be used for a bio_split() replacement, and it turns out to be
very useful in a fair amount of driver code - a fair number of drivers
were implementing this in their own roundabout ways, often painfully.

Note that this means it's no longer to call bio_endio() more than once
on the same bio! This can cause problems for drivers that save/restore
bi_end_io. Arguably they shouldn't be saving/restoring bi_end_io at all
- in all but the simplest cases they'd be better off just cloning the
bio, and immutable biovecs is making bio cloning cheaper. But for now,
we add a bio_endio_nodec() for these cases.

Signed-off-by: Kent Overstreet <kmo@daterainc.com>
Cc: Jens Axboe <axboe@kernel.dk>

2 files changed, 4 insertions, 0 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 0c32a45a419c..64f5169c224b 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -356,6 +356,7 @@ static inline struct bio *bio_clone_kmalloc(struct bio *bio, gfp_t gfp_mask)
 }
 
 extern void bio_endio(struct bio *, int);
+extern void bio_endio_nodec(struct bio *, int);
 struct request_queue;
 extern int bio_phys_segments(struct request_queue *, struct bio *);
 
@@ -364,6 +365,7 @@ extern void bio_advance(struct bio *, unsigned);
 
 extern void bio_init(struct bio *);
 extern void bio_reset(struct bio *);
+void bio_chain(struct bio *, struct bio *);
 
 extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
 extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d369f8f6af79..bbc3a6c88fce 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -65,6 +65,8 @@ struct bio {
         unsigned int            bi_seg_front_size;
         unsigned int            bi_seg_back_size;
 
+        atomic_t                bi_remaining;
+
         bio_end_io_t            *bi_end_io;
 
         void                    *bi_private;