5-11 インターフェースのdown

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>

int
main()
{
  int soc;
  struct sockaddr_nl sa;
  char buf[4096];
  int n;
  int seq=100;
  struct nlmsghdr *nlhdr;
  struct ifinfomsg *ifihdr;

  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;

  memset(buf, 0, sizeof(buf));
  nlhdr = (struct nlmsghdr *)buf;
  ifihdr = NLMSG_DATA(nlhdr);
  nlhdr->nlmsg_type = RTM_SETLINK; /* (1) */
  nlhdr->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK; /* (2) */
  nlhdr->nlmsg_pid = 0;
  seq++;
  nlhdr->nlmsg_seq = seq;

  /* (3) */
  ifihdr->ifi_family = AF_UNSPEC;
  ifihdr->ifi_type = ARPHRD_LOOPBACK; /* lo is loopback */
  ifihdr->ifi_index = if_nametoindex("lo");

  /* (4) */
  /* "UP & RUNNING"にするには、ifi_flagsを以下に変更 */
  /*
  ifihdr->ifi_flags = IFF_UP | IFF_RUNNING;
  */
  ifihdr->ifi_flags = 0;
  ifihdr->ifi_change = IFF_UP | IFF_RUNNING;
  nlhdr->nlmsg_len = sizeof(struct nlmsghdr) + NLMSG_LENGTH(sizeof(struct ifinfomsg));

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

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

  printf("recv\n");
  /* (5) */
  for (nlhdr = (struct nlmsghdr *)buf; NLMSG_OK(nlhdr, n);
       nlhdr = NLMSG_NEXT(nlhdr, n)) {
    printf("len : %d\n", nlhdr->nlmsg_len);
    printf("type : %d\n", nlhdr->nlmsg_type);

    if (nlhdr->nlmsg_type == NLMSG_ERROR) {
      struct nlmsgerr *errmsg;

      /* (6) */
      errmsg = NLMSG_DATA(nlhdr);
      printf("%d, %s\n", errmsg->error, strerror(-errmsg->error));
    }
  }

  close(soc);

  return 0;
}

拙著「Linuxネットワークプログラミング」の紹介