SE Wiki/LKP

Linux Kernel programming

Netlink

Пример использования протокола Netlink из пространства пользователя Программа, получающая список сетевых интерфейсов через RtNetlink:

#include <stdio.h>
#include <string.h>
#include <errno.h>

#include <unistd.h>

#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>

// ================================================================================

static char buf[10240];

int main(int argc, char** argv) {
  int nlsock;
  struct sockaddr_nl nla;

  nlsock = socket(AF_NETLINK, SOCK_DGRAM, NETLINK_ROUTE);
  if (nlsock < 0) {
    printf("Failed to create a Netlink socket: %s\n", strerror(errno));
    return 1;
  }

  nla.nl_family = AF_NETLINK;
  nla.nl_pad = 0;
  nla.nl_pid = 0;
  nla.nl_groups = 0;
  if (connect(nlsock, (const struct sockaddr*)&nla, sizeof(nla)) < 0) {
    printf("Failed to connect to the kernel rtnetlink: %s\n", strerror(errno));
    goto close_sock;
  }

  struct nlmsghdr* nlh = (struct nlmsghdr*)buf;
  nlh->nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
  nlh->nlmsg_type = RTM_GETLINK;
  nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_DUMP;
  nlh->nlmsg_seq = 0;
  nlh->nlmsg_pid = getpid();

  struct ifinfomsg* msg = (struct ifinfomsg*)NLMSG_DATA(nlh);
  msg->ifi_family = AF_UNSPEC;
  msg->ifi_index = 1;
  msg->ifi_change = 0xFFFFFFFF;

  if (send(nlsock, buf, nlh->nlmsg_len, 0) < 0) {
    printf("Failed to send a Netlink message: %s\n", strerror(errno));
    goto close_sock;
  }

  int sz = recv(nlsock, buf, sizeof(buf), 0);

  while (NLMSG_OK(nlh, sz) && nlh->nlmsg_type != NLMSG_DONE) {
    if (nlh->nlmsg_type & NLMSG_ERROR) {
      struct nlmsgerr* e = (struct nlmsgerr*)NLMSG_DATA(nlh);
      printf("Failed to get a link: %d (%s)\n", e->error, strerror(-e->error));
      goto close_sock;
    }

    if (nlh->nlmsg_type & RTM_NEWLINK) {
      struct rtattr* pattr;
      struct ifinfomsg* msg = (struct ifinfomsg*)NLMSG_DATA(nlh);

      pattr = (struct rtattr*)(msg + 1);
      int alen = (char*)(nlh + nlh->nlmsg_len) - (char*)pattr;

      while (RTA_OK(pattr, alen)) {
        if (pattr->rta_type == IFLA_IFNAME) {
          printf("Interface %d, name %.*s\n", msg->ifi_index, RTA_PAYLOAD(pattr), RTA_DATA(pattr));
        }

        pattr = RTA_NEXT(pattr, alen);
      }
    }

    nlh = NLMSG_NEXT(nlh, sz);
  }

 close_sock:
  close(nlsock);

  return 0;
}