[PATCH] make bio->bi_end_io() optional

Sometimes we don't even need a bio->bi_end_io, so make it optional. This
also encourages users to _use_ bio_endio()! I like that, since it means
they don't have to remember to decrement bi_size themselves.

Also clear bi_private in bio_init(), and switch to subsys_initcall().

drivers/block/ll_rw_blk.c

@@ -1941,7 +1941,6 @@ int submit_bio(int rw, struct bio *bio)
 {
 	int count = bio_sectors(bio);
 
-	BUG_ON(!bio->bi_end_io);
 	BIO_BUG_ON(!bio->bi_size);
 	BIO_BUG_ON(!bio->bi_io_vec);
 	bio->bi_rw = rw;

drivers/block/umem.c

@@ -548,12 +548,7 @@ static void process_page(unsigned long data)
 
 		return_bio = bio->bi_next;
 		bio->bi_next = NULL;
-		/* should use bio_endio(), however already cleared
-		 * BIO_UPTODATE. so set bio->bi_size = 0 manually to indicate
-		 * completely done
-		 */
-		bio->bi_size = 0;
-		bio->bi_end_io(bio, bytes, 0);
+		bio_endio(bio, bio->bi_size, 0);
 	}
 }
 

fs/bio.c

@@ -122,6 +122,7 @@ inline void bio_init(struct bio *bio)
 	bio->bi_max_vecs = 0;
 	bio->bi_end_io = NULL;
 	atomic_set(&bio->bi_cnt, 1);
+	bio->bi_private = NULL;
 }
 
 /**
@@ -452,14 +453,15 @@ int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
  * @error:	error, if any
  *
  * Description:
- *   bio_endio() will end I/O @bytes_done number of bytes. This may be just
- *   a partial part of the bio, or it may be the whole bio. bio_endio() is
- *   the preferred way to end I/O on a bio, it takes care of decrementing
+ *   bio_endio() will end I/O on @bytes_done number of bytes. This may be
+ *   just a partial part of the bio, or it may be the whole bio. bio_endio()
+ *   is the preferred way to end I/O on a bio, it takes care of decrementing
  *   bi_size and clearing BIO_UPTODATE on error. @error is 0 on success, and
  *   and one of the established -Exxxx (-EIO, for instance) error values in
- *   case something went wrong.
+ *   case something went wrong. Noone should call bi_end_io() directly on
+ *   a bio unless they own it and thus know that it has an end_io function.
  **/
-int bio_endio(struct bio *bio, unsigned int bytes_done, int error)
+void bio_endio(struct bio *bio, unsigned int bytes_done, int error)
 {
 	if (error)
 		clear_bit(BIO_UPTODATE, &bio->bi_flags);
@@ -471,7 +473,9 @@ int bio_endio(struct bio *bio, unsigned int bytes_done, int error)
 	}
 
 	bio->bi_size -= bytes_done;
-	return bio->bi_end_io(bio, bytes_done, error);
+
+	if (bio->bi_end_io)
+		bio->bi_end_io(bio, bytes_done, error);
 }
 
 static void __init biovec_init_pools(void)
@@ -543,7 +547,7 @@ static int __init init_bio(void)
 	return 0;
 }
 
-module_init(init_bio);
+subsys_initcall(init_bio);
 
 EXPORT_SYMBOL(bio_alloc);
 EXPORT_SYMBOL(bio_put);

include/linux/bio.h

@@ -202,7 +202,7 @@ struct bio {
 extern struct bio *bio_alloc(int, int);
 extern void bio_put(struct bio *);
 
-extern int bio_endio(struct bio *, unsigned int, int);
+extern void 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 *);