nbd: add function to convert blk req op to nbd cmd

This adds a helper function to convert a block req op to a nbd cmd type.
It will be used in the last patch to log the type in the timeout
handler.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -344,6 +344,22 @@ static void sock_shutdown(struct nbd_device *nbd)
 	dev_warn(disk_to_dev(nbd->disk), "shutting down sockets\n");
 }
 
+static u32 req_to_nbd_cmd_type(struct request *req)
+{
+	switch (req_op(req)) {
+	case REQ_OP_DISCARD:
+		return NBD_CMD_TRIM;
+	case REQ_OP_FLUSH:
+		return NBD_CMD_FLUSH;
+	case REQ_OP_WRITE:
+		return NBD_CMD_WRITE;
+	case REQ_OP_READ:
+		return NBD_CMD_READ;
+	default:
+		return U32_MAX;
+	}
+}
+
 static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 						 bool reserved)
 {
@@ -480,22 +496,9 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 
 	iov_iter_kvec(&from, WRITE, &iov, 1, sizeof(request));
 
-	switch (req_op(req)) {
-	case REQ_OP_DISCARD:
-		type = NBD_CMD_TRIM;
-		break;
-	case REQ_OP_FLUSH:
-		type = NBD_CMD_FLUSH;
-		break;
-	case REQ_OP_WRITE:
-		type = NBD_CMD_WRITE;
-		break;
-	case REQ_OP_READ:
-		type = NBD_CMD_READ;
-		break;
-	default:
+	type = req_to_nbd_cmd_type(req);
+	if (type == U32_MAX)
 		return -EIO;
-	}
 
 	if (rq_data_dir(req) == WRITE &&
 	    (config->flags & NBD_FLAG_READ_ONLY)) {