使用netlink方式，监听dhcp客户端的IP地址

当机器联网后，会启动dhcpcd客户端程序获得ip，下面写一个netlink程序，监听

一下所获得的ip地址。代码很简陋，仅仅用于测试使用。

#define WM "eth0"static int recv_netlink_ip(int fd){static char buf[512];char *devname;struct iovec iov = {buf, sizeof(buf) };struct sockaddr_nl sa;struct msghdr msg = {(void *)&sa, sizeof(sa), &iov, 1, NULL, 0, 0};struct nlmsghdr *nlh;int len, index;struct ifinfomsg *ifi;struct ifinfomsg *pstruIF; struct nlmsgerr *pstruError;struct rtattr *pstruAttr;int nAttrLen;struct ifaddrmsg *ifa;struct rtattr *rth;int rtl;char name[IFNAMSIZ];uint32_t ipaddr;struct rtattr *rta;int ret = 0;int left;static char empty_ip[128];len = recvmsg(fd, &msg, 0);if (len <= (sizeof(struct nlmsghdr)+sizeof(struct ifinfomsg))) {printf("recvmsg(%d), len=%d\n", fd, len);goto out;}left = len;nlh = (struct nlmsghdr *)buf;while (NLMSG_OK(nlh, left)){switch(nlh->nlmsg_type){case RTM_NEWLINK:break;case RTM_DELLINK:break;case RTM_NEWADDR:ifa = (struct ifaddrmsg *) NLMSG_DATA (nlh);rth = IFA_RTA (ifa);rtl = IFA_PAYLOAD (nlh);for (;rtl && RTA_OK (rth, rtl); rth = RTA_NEXT (rth,rtl)){if (rth->rta_type != IFA_LOCAL) continue;ipaddr = * ((uint32_t *)RTA_DATA(rth));ipaddr = htonl(ipaddr);printf ("%s added %X\n",if_indextoname(ifa->ifa_index,name),ipaddr);printf("%s is now %d.%d.%d.%d\n",name,(ipaddr >> 24) & 0xff,(ipaddr >> 16) & 0xff,(ipaddr >> 8) & 0xff,ipaddr & 0xff);}if(strcmp(WM, if_indextoname(ifa->ifa_index,name)) == 0){}break;  /* ip */case RTM_DELADDR:ifa = (struct ifaddrmsg *) NLMSG_DATA (nlh);rth = IFA_RTA (ifa);rtl = IFA_PAYLOAD (nlh);for (;rtl && RTA_OK (rth, rtl); rth = RTA_NEXT (rth,rtl)){if (rth->rta_type != IFA_LOCAL) continue;ipaddr = * ((uint32_t *)RTA_DATA(rth));ipaddr = htonl(ipaddr);printf ("%s added %X\n",if_indextoname(ifa->ifa_index,name),ipaddr);printf("%s is now %d.%d.%d.%d\n",name,(ipaddr >> 24) & 0xff,(ipaddr >> 16) & 0xff,(ipaddr >> 8) & 0xff,ipaddr & 0xff);}if(strcmp(WM, if_indextoname(ifa->ifa_index,name)) == 0){}break; /* del ip*/case RTM_GETADDR:break;case NLMSG_DONE:break;case NLMSG_ERROR:pstruError = (struct nlmsgerr *)NLMSG_DATA(nlh);printf("error : [%s]\n",strerror(-pstruError -> error));break;}nlh = NLMSG_NEXT(nlh, left);}out:return ret;}int  check_ip(){int fd;struct sockaddr_nl sa;int ret;fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);if (fd < 0) {return -1;}memset(&sa, 0, sizeof(sa));sa.nl_family = AF_NETLINK;sa.nl_groups = RTMGRP_IPV4_IFADDR;if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0){close(fd);return -1;}while (1){ret = recv_netlink_ip(fd);if (ret < 0){printf("recv ip break \n");break;}}return 0;}