5-14 IPアドレスの取得

#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;
  struct {
    struct nlmsghdr nh;
    struct ifaddrmsg ifa;
  } request;
  int seq = 100;
  int n;
  char buf[4096];
  struct nlmsghdr *nlhdr;

  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 = 0;

  request.nh.nlmsg_len = sizeof(request);
  request.nh.nlmsg_type = RTM_GETADDR;
  request.nh.nlmsg_flags = NLM_F_ROOT | NLM_F_REQUEST;
  request.nh.nlmsg_pid = 0;
  seq++;
  request.nh.nlmsg_seq = seq;
  request.ifa.ifa_family = AF_INET;

  n = sendto(soc, (void *)&request, sizeof(request), 0,
             (struct sockaddr *)&sa, sizeof(sa));
  if (n < 0) {
    perror("sendto");
    return 1;
  }

  printf("recv\n");

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

  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) {
      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)) {
      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:
        {
        char str[128];
        char *addrptr = RTA_DATA(rta);
        inet_ntop(addrmsg->ifa_family, addrptr, str, sizeof(str));
        printf(" + %s\n", str);
        }
        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