UDL_CMD_MAX_XFER_SIZE
cx->buf = usbd_alloc_buffer(cx->xfer, UDL_CMD_MAX_XFER_SIZE);
cb->buf = malloc(UDL_CMD_MAX_XFER_SIZE, M_USBDEV, M_NOWAIT|M_ZERO);
free(cb->buf, M_USBDEV, UDL_CMD_MAX_XFER_SIZE);
if (total > UDL_CMD_MAX_XFER_SIZE) {