hallmonitor.c

#include <stdio.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <linux/connector.h>
#include <linux/cn_proc.h>
#include <stdlib.h>
#include <errno.h>

struct __attribute__ ((aligned(NLMSG_ALIGNTO))) nlcn_msg {
  struct nlmsghdr nl_hdr;
  struct __attribute__ ((__packed__)) {
    struct cn_msg cn_msg;
    enum proc_cn_mcast_op cn_mcast;
  };
};

struct __attribute__ ((aligned(NLMSG_ALIGNTO))) nlcn_proc_event {
  struct nlmsghdr nl_hdr;
  struct __attribute__ ((__packed__)) {
    struct cn_msg cn_msg;
    struct proc_event event;
  };
};


static const struct nlcn_msg nilmsg;
static const struct nlcn_proc_event nilevent;

int main(int argc, const char *argv[])
{
  int nl_sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_CONNECTOR);
  struct sockaddr_nl sa_nl;

  if (nl_sock == -1) {
    perror("Problem opening NETLINK socket!");
    exit(-1);
  }

  sa_nl.nl_family = AF_NETLINK;
  sa_nl.nl_groups = CN_IDX_PROC;
  sa_nl.nl_pid = getpid();

  if (bind(nl_sock, (struct sockaddr*)&sa_nl, sizeof(sa_nl)) != 0) {
    perror("Problem binding NETLINK socket!");
    close(nl_sock);
    exit(-1);
  }

  struct nlcn_msg msg = nilmsg;

  msg.nl_hdr.nlmsg_len = sizeof(struct nlcn_msg);
  msg.nl_hdr.nlmsg_type = NLMSG_DONE;

  msg.cn_msg.id.idx = CN_IDX_PROC;
  msg.cn_msg.id.val = CN_VAL_PROC;
  msg.cn_msg.len = sizeof(enum proc_cn_mcast_op);
  msg.cn_mcast = PROC_CN_MCAST_LISTEN;

  if (send(nl_sock, &msg, sizeof(msg), 0) == -1) {
    perror("Problem sending NETLINK registration message!");
    close(nl_sock);
    exit(-1);
  }

  int rc = 0;
  struct nlcn_proc_event ev = nilevent;

  while(1) {
    rc = recv(nl_sock, &ev, sizeof(ev), 0);

    if (rc == 0) {
      exit(0);
    }
    else if (rc == -1) {
      if (errno == EINTR) continue;
      perror("Problem during NETLINK recv()!");
      close(nl_sock);
      exit(-1);
    }

    if (ev.event.what == PROC_EVENT_UID) {
      printf("id change: pid=%d tgid=%d\n",
          ev.event.event_data.id.process_pid,
          ev.event.event_data.id.process_tgid);
    }
  }
}