#include <bits/types/sigset_t.h>
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>

// vorgegriffen, man benötigt bei sister nur SIG_IGN
void handle_signal(int sig) {
  int errno_old = errno;
  const char str[] = "Hallo aus handle_signal\n";
  write(STDOUT_FILENO, str, sizeof(str));
  errno = errno_old;
  // nichts
}

void start_child() {
  pid_t pid = fork();
  switch (pid) {
    case 0:
      // Fehlerbehandlung
      int fd = open("baz", O_RDONLY);
      // Fehlerbehandlung
      dup2(fd, STDIN_FILENO);
      execlp("cat", "cat", NULL);
      break;
    case -1:
      perror("fork");
      break;
    default:
      // Elter
      break;
  }
}
int main() {
  struct sigaction act = {
    .sa_handler = handle_signal,
  };
  sigaction(SIGUSR1, &act, NULL);
  
  while (1) {
    sigset_t set;
    sigemptyset(&set);
    sigsuspend(&set);
    printf("SIGUSR1. waiting 5 seconds\n");
    sigset_t set2, old;
    sigemptyset(&set2);
    sigaddset(&set2, SIGINT);
    sigprocmask(SIG_BLOCK, &set2, &old);
    sleep(5);
    start_child();
    // auch mit unblock möglich
    sigprocmask(SIG_SETMASK, &old, NULL);
  }
}