ulog.c

#include <asm/types.h>
#include <linux/netlink.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <unistd.h>

int main() {
  int res;

  int s = socket(AF_NETLINK, SOCK_RAW, NETLINK_NFLOG);

  if (s == -1) {
    perror("Error creating netlink socket");
    return 1;
  }

  struct sockaddr_nl addr = {
    .nl_family = AF_NETLINK,
    .nl_pad = 0,
    .nl_pid = 0,
    .nl_groups = 1
  };
  res = bind(s, (struct sockaddr *)&addr, sizeof(addr));
  if (res == -1) {
    perror("Error binding to log channel");
    return 1;
  }

  for (;;) {
    uint8_t buffer[65536];
    memset(buffer, 0, sizeof(buffer));

    ssize_t nr = recv(s, buffer, sizeof(buffer), 0);
    if (nr == -1) {
      perror("Error reading packet data from netlink");
      return 1;
    }

    res = write(1, buffer, nr);
    if (res != nr) {
      perror("Error writing packet data to stdout");
      return 1;
    }
  }
}