block: fold cmd_type into the REQ_OP_ space

Instead of keeping two levels of indirection for requests types, fold it
all into the operations.  The little caveat here is that previously
cmd_type only applied to struct request, while the request and bio op
fields were set to plain REQ_OP_READ/WRITE even for passthrough
operations.

Instead this patch adds new REQ_OP_* for SCSI passthrough and driver
private requests, althought it has to add two for each so that we
can communicate the data in/out nature of the request.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/mtd/ubi/block.c

@@ -323,16 +323,15 @@ static int ubiblock_queue_rq(struct blk_mq_hw_ctx *hctx,
 	struct ubiblock *dev = hctx->queue->queuedata;
 	struct ubiblock_pdu *pdu = blk_mq_rq_to_pdu(req);
 
-	if (req->cmd_type != REQ_TYPE_FS)
+	switch (req_op(req)) {
+	case REQ_OP_READ:
+		ubi_sgl_init(&pdu->usgl);
+		queue_work(dev->wq, &pdu->work);
+		return BLK_MQ_RQ_QUEUE_OK;
+	default:
 		return BLK_MQ_RQ_QUEUE_ERROR;
+	}
 
-	if (rq_data_dir(req) != READ)
-		return BLK_MQ_RQ_QUEUE_ERROR; /* Write not implemented */
-
-	ubi_sgl_init(&pdu->usgl);
-	queue_work(dev->wq, &pdu->work);
-
-	return BLK_MQ_RQ_QUEUE_OK;
 }
 
 static int ubiblock_init_request(void *data, struct request *req,