串口通信如何同步模式超时读取？

fd = open(device, O_RDWR | O_NOCTTY);

    fd_set read_fds, write_fds, except_fds;
    FD_ZERO(&read_fds);
    FD_ZERO(&write_fds);
    FD_ZERO(&except_fds);
    FD_SET(fd, &read_fds);
// Set timeout to 1.0 seconds
    struct timeval timeout;
    timeout.tv_sec = 2;
    timeout.tv_usec = 0;
    if (select(fd + 1, &read_fds, &write_fds, &except_fds, &timeout) != 1)
    {
        return -1;  // 超时
    }
    else {
	//正常读取操作
       len = read(fd, &res, sizeof(res));
    }