5-15 IPアドレス変更通知の受け取り

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <linux/rtnetlink.h>

int
main()
{
  int soc;
  struct sockaddr_nl sa;
  int n;
  char buf[4096];
  struct nlmsghdr *nlhdr;
  char ipaddrstr[48];

  soc = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);

  memset(&sa, 0, sizeof(sa));
  sa.nl_family = AF_NETLINK;
  sa.nl_pid = 0; /* kernel */
  sa.nl_groups = RTMGRP_IPV4_IFADDR;

  if (bind(soc, (struct sockaddr *)&sa, sizeof(sa)) != 0) {
    perror("bind");
    return 1;
  }

  while (1) {

    printf("before recv()\n");

    n = recv(soc, buf, sizeof(buf), 0);
    if (n < 0) {
      perror("recv");
      return 1;
    }

    printf("after recv()\n");

    for (nlhdr = (struct nlmsghdr *)buf; NLMSG_OK(nlhdr, n);
          nlhdr = NLMSG_NEXT(nlhdr, n)) {
      struct ifaddrmsg *addrmsg;
      struct rtattr *rta;
      int n;

      printf("====\n");
      printf("len : %d\n", nlhdr->nlmsg_len);
      printf("type : %d\n", nlhdr->nlmsg_type);

      if (nlhdr->nlmsg_type != RTM_NEWADDR
            && nlhdr->nlmsg_type != RTM_DELADDR) {
        continue;
      }

      addrmsg = NLMSG_DATA(nlhdr);

      printf(" family : %d\n", addrmsg->ifa_family);
      printf(" prefixlen : %d\n", addrmsg->ifa_prefixlen);
      printf(" flags : %d\n", addrmsg->ifa_flags);
      printf(" scope : %d\n", addrmsg->ifa_scope);
      printf(" index : %d\n", addrmsg->ifa_index);

      n = nlhdr->nlmsg_len - NLMSG_LENGTH(sizeof(struct ifaddrmsg));

      for (rta = IFA_RTA(addrmsg); RTA_OK(rta, n); rta = RTA_NEXT(rta, n)) {
        struct in_addr *ina;

        printf(" type=%d, len=%d\n", rta->rta_type, rta->rta_len);

        switch (rta->rta_type) {
        case IFA_ADDRESS:
        case IFA_BROADCAST:
        case IFA_LOCAL:
          ina = RTA_DATA(rta);
          inet_ntop(addrmsg->ifa_family, ina, ipaddrstr, sizeof(ipaddrstr));
          printf(" + %s\n", ipaddrstr);
          break;

        case IFA_LABEL:
          printf(" + %s\n", (char *)RTA_DATA(rta));
          break;

        default:
          printf(" + other type\n");
          break;
        }
      }
    }
  }

  close(soc);

  return 0;
}

拙著「Linuxネットワークプログラミング」の紹介