recv.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/socket.h>
#include <linux/netlink.h>

#define MYGRP 17

#define MAX_PAYLOAD 1024  /* maximum payload size*/


void read_event(int sock)
{
  struct sockaddr_nl nladdr;
  struct msghdr msg;
  struct iovec iov;
  char buffer[65536];
  int ret;

  iov.iov_base = (void *) buffer;
  iov.iov_len = sizeof(buffer);
  msg.msg_name = (void *) &(nladdr);
  msg.msg_namelen = sizeof(nladdr);
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;

  printf("Listen for message...\n");
  ret = recvmsg(sock, &msg, 0);
  if (ret < 0)
      return;

  char *payload = NLMSG_DATA((struct nlmsghdr *) &buffer);
  printf("Received from kernel: %s\n", payload);
}

int main(int argc, char **argv)
{
  struct sockaddr_nl src_addr;
  //struct sockaddr_nl dest_addr;
  //struct nlmsghdr *nlh;
  //struct msghdr msg;
  //struct iovec iov;
  int sock_fd;
  //int rc;


  sock_fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_USERSOCK);
  if (sock_fd < 0) {
    printf("socket(): %s\n", strerror(errno));
    return 1;
  }

  memset(&src_addr, 0, sizeof(src_addr));
  src_addr.nl_family = AF_NETLINK;
  //src_addr.nl_pid = getpid();  /* self pid */
  src_addr.nl_pid = 0; //from kernel?
  //src_addr.nl_groups = 0;  /* not in mcast groups */
  bind(sock_fd, (struct sockaddr*)&src_addr, sizeof(src_addr));


  int group = MYGRP;
  if (setsockopt(sock_fd, SOL_NETLINK, NETLINK_ADD_MEMBERSHIP, &group, sizeof(group)) < 0) {
    printf("setsockopt(NETLINK_ADD_MEMBERSHIP): %s\n", strerror(errno));
    close(sock_fd);
    return 1;
  }


  while (1) {
    read_event(sock_fd);
  }

  close(sock_fd);

  return 0;
}