blk-mq: allow drivers to hook into I/O completion

Split out the bottom half of blk_mq_end_io so that drivers can perform
work when they know a request has been completed, but before it has been
freed.  This also obsoletes blk_mq_end_io_partial as drivers can now
pass any value to blk_update_request directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index a4ea0ce..a81b474 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -149,13 +149,8 @@
 struct blk_mq_hw_ctx *blk_mq_alloc_single_hw_queue(struct blk_mq_tag_set *, unsigned int);
 void blk_mq_free_single_hw_queue(struct blk_mq_hw_ctx *, unsigned int);
 
-bool blk_mq_end_io_partial(struct request *rq, int error,
-		unsigned int nr_bytes);
-static inline void blk_mq_end_io(struct request *rq, int error)
-{
-	bool done = !blk_mq_end_io_partial(rq, error, blk_rq_bytes(rq));
-	BUG_ON(!done);
-}
+void blk_mq_end_io(struct request *rq, int error);
+void __blk_mq_end_io(struct request *rq, int error);
 
 void blk_mq_complete_request(struct request *rq);