https://www.kernel.org/doc/Documentation/networking/tuntap.txt 虚拟网卡 TUN/TAP 驱动程序设计原理 https://www.ibm.com/developerworks/cn/linux/l-tuntap/ Linux串口上网的简单实现 https://www.ibm.com/developerworks/cn/linux/l-serialnet/index.html