#include <mqueue.h>
#include <pthread.h>
#include <errno.h>
#include <sys/socket.h>
#include <signal.h>
#include <unistd.h>
#include "syscall.h"

struct args {
  pthread_barrier_t barrier;
  int sock;
  const struct sigevent* sev;
};

static void* start(void* p) {
  struct args* args = p;
  char buf[32];
  ssize_t n;
  int s = args->sock;
  void (*func)(union sigval) = args->sev->sigev_notify_function;
  union sigval val = args->sev->sigev_value;

  pthread_barrier_wait(&args->barrier);
  n = recv(s, buf, sizeof(buf), MSG_NOSIGNAL | MSG_WAITALL);
  close(s);
  if (n == sizeof buf && buf[sizeof buf - 1] == 1)
    func(val);
  return 0;
}

int mq_notify(mqd_t mqd, const struct sigevent* sev) {
  struct args args = {.sev = sev};
  pthread_attr_t attr;
  pthread_t td;
  int s;
  struct sigevent sev2;
  static const char zeros[32];

  if (!sev || sev->sigev_notify != SIGEV_THREAD)
    return syscall(SYS_mq_notify, mqd, sev);

  s = socket(AF_NETLINK, SOCK_RAW | SOCK_CLOEXEC, 0);
  if (s < 0)
    return -1;
  args.sock = s;

  if (sev->sigev_notify_attributes)
    attr = *sev->sigev_notify_attributes;
  else
    pthread_attr_init(&attr);
  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
  pthread_barrier_init(&args.barrier, 0, 2);

  if (pthread_create(&td, &attr, start, &args)) {
    __syscall(SYS_close, s);
    errno = EAGAIN;
    return -1;
  }

  pthread_barrier_wait(&args.barrier);
  pthread_barrier_destroy(&args.barrier);

  sev2.sigev_notify = SIGEV_THREAD;
  sev2.sigev_signo = s;
  sev2.sigev_value.sival_ptr = (void*)&zeros;

  if (syscall(SYS_mq_notify, mqd, &sev2) < 0) {
    pthread_cancel(td);
    __syscall(SYS_close, s);
    return -1;
  }

  return 0;
}