blk-mq: do not initialize req->special

Drivers can reach their private data easily using the blk_mq_rq_to_pdu
helper and don't need req->special.  By not initializing it code can
be simplified nicely, and we also shave off a few more instructions from
the I/O path.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-flush.c

@@ -306,22 +306,16 @@ static bool blk_kick_flush(struct request_queue *q)
 	 */
 	q->flush_pending_idx ^= 1;
 
+	blk_rq_init(q, q->flush_rq);
 	if (q->mq_ops) {
-		struct blk_mq_ctx *ctx = first_rq->mq_ctx;
-		struct blk_mq_hw_ctx *hctx = q->mq_ops->map_queue(q, ctx->cpu);
-
-		blk_mq_rq_init(hctx, q->flush_rq);
-		q->flush_rq->mq_ctx = ctx;
-
 		/*
 		 * Reuse the tag value from the fist waiting request,
 		 * with blk-mq the tag is generated during request
 		 * allocation and drivers can rely on it being inside
 		 * the range they asked for.
 		 */
+		q->flush_rq->mq_ctx = first_rq->mq_ctx;
 		q->flush_rq->tag = first_rq->tag;
-	} else {
-		blk_rq_init(q, q->flush_rq);
 	}
 
 	q->flush_rq->cmd_type = REQ_TYPE_FS;

block/blk-mq.c

@@ -251,24 +251,13 @@ struct request *blk_mq_alloc_reserved_request(struct request_queue *q, int rw,
 }
 EXPORT_SYMBOL(blk_mq_alloc_reserved_request);
 
-/*
- * Re-init and set pdu, if we have it
- */
-void blk_mq_rq_init(struct blk_mq_hw_ctx *hctx, struct request *rq)
-{
-	blk_rq_init(hctx->queue, rq);
-
-	if (hctx->cmd_size)
-		rq->special = blk_mq_rq_to_pdu(rq);
-}
-
 static void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx,
 				  struct blk_mq_ctx *ctx, struct request *rq)
 {
 	const int tag = rq->tag;
 	struct request_queue *q = rq->q;
 
-	blk_mq_rq_init(hctx, rq);
+	blk_rq_init(hctx->queue, rq);
 	blk_mq_put_tag(hctx->tags, tag);
 
 	blk_mq_queue_exit(q);
@@ -1165,7 +1154,7 @@ static int blk_mq_init_rq_map(struct blk_mq_hw_ctx *hctx,
 		left -= to_do * rq_size;
 		for (j = 0; j < to_do; j++) {
 			hctx->rqs[i] = p;
-			blk_mq_rq_init(hctx, hctx->rqs[i]);
+			blk_rq_init(hctx->queue, hctx->rqs[i]);
 			p += rq_size;
 			i++;
 		}

block/blk-mq.h

@@ -27,7 +27,6 @@ void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async);
 void blk_mq_init_flush(struct request_queue *q);
 void blk_mq_drain_queue(struct request_queue *q);
 void blk_mq_free_queue(struct request_queue *q);
-void blk_mq_rq_init(struct blk_mq_hw_ctx *hctx, struct request *rq);
 
 /*
  * CPU hotplug helpers

drivers/block/null_blk.c

@@ -226,7 +226,7 @@ static void null_cmd_end_timer(struct nullb_cmd *cmd)
 
 static void null_softirq_done_fn(struct request *rq)
 {
-	end_cmd(rq->special);
+	end_cmd(blk_mq_rq_to_pdu(rq));
 }
 
 static inline void null_handle_cmd(struct nullb_cmd *cmd)
@@ -311,7 +311,7 @@ static void null_request_fn(struct request_queue *q)
 
 static int null_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *rq)
 {
-	struct nullb_cmd *cmd = rq->special;
+	struct nullb_cmd *cmd = blk_mq_rq_to_pdu(rq);
 
 	cmd->rq = rq;
 	cmd->nq = hctx->driver_data;

drivers/block/virtio_blk.c

@@ -112,7 +112,7 @@ static int __virtblk_add_req(struct virtqueue *vq,
 
 static inline void virtblk_request_done(struct request *req)
 {
-	struct virtblk_req *vbr = req->special;
+	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
 	int error = virtblk_result(vbr);
 
 	if (req->cmd_type == REQ_TYPE_BLOCK_PC) {
@@ -154,7 +154,7 @@ static void virtblk_done(struct virtqueue *vq)
 static int virtio_queue_rq(struct blk_mq_hw_ctx *hctx, struct request *req)
 {
 	struct virtio_blk *vblk = hctx->queue->queuedata;
-	struct virtblk_req *vbr = req->special;
+	struct virtblk_req *vbr = blk_mq_rq_to_pdu(req);
 	unsigned long flags;
 	unsigned int num;
 	const bool last = (req->cmd_flags & REQ_END) != 0;
@@ -501,7 +501,7 @@ static int virtblk_init_vbr(void *data, struct blk_mq_hw_ctx *hctx,
 			     struct request *rq, unsigned int nr)
 {
 	struct virtio_blk *vblk = data;
-	struct virtblk_req *vbr = rq->special;
+	struct virtblk_req *vbr = blk_mq_rq_to_pdu(rq);
 
 	sg_init_table(vbr->sg, vblk->sg_elems);
 	return 0;