#include <pty.h>
#include <utmp.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <pthread.h>

int forkpty(int* pm,
            char* name,
            const struct termios* tio,
            const struct winsize* ws) {
  int m, s, ec = 0, p[2], cs;
  pid_t pid = -1;
  sigset_t set, oldset;

  if (openpty(&m, &s, name, tio, ws) < 0)
    return -1;

  sigfillset(&set);
  pthread_sigmask(SIG_BLOCK, &set, &oldset);
  pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);

  if (pipe2(p, O_CLOEXEC)) {
    close(s);
    goto out;
  }

  pid = fork();
  if (!pid) {
    close(m);
    close(p[0]);
    if (login_tty(s)) {
      write(p[1], &errno, sizeof errno);
      _exit(127);
    }
    close(p[1]);
    pthread_setcancelstate(cs, 0);
    pthread_sigmask(SIG_SETMASK, &oldset, 0);
    return 0;
  }
  close(s);
  close(p[1]);
  if (read(p[0], &ec, sizeof ec) > 0) {
    int status;
    waitpid(pid, &status, 0);
    pid = -1;
    errno = ec;
  }
  close(p[0]);

out:
  if (pid > 0)
    *pm = m;
  else
    close(m);

  pthread_setcancelstate(cs, 0);
  pthread_sigmask(SIG_SETMASK, &oldset, 0);

  return pid;
}