my_init.c

#include <assert.h>

#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#include <sys/procctl.h>

extern int errno;

static void
print_proc_reap_status(pid_t my_pid)
{
  struct procctl_reaper_status rst;
  int err = procctl(P_PID, my_pid, PROC_REAP_STATUS, &rst);
  if (err == 0) {
    printf("success\n");
    printf("flags: %u\n", rst.rs_flags);
    printf("  REAPER_STATUS_OWNED: %s\n",
           (rst.rs_flags & REAPER_STATUS_OWNED)
           ? "true" : "false");
    printf("  REAPER_STATUS_REALINIT: %s\n",
           (rst.rs_flags & REAPER_STATUS_REALINIT)
           ? "true" : "false");
    printf("children: %u\n", rst.rs_children);
    printf("reaper: %d\n", rst.rs_reaper);
    printf("pid: %d\n", rst.rs_pid);
  } else if (err == -1) {
    fprintf(stderr, "error\n");
    fprintf(stderr, "%s\n", strerror(errno));
  } else {
    assert(0);
  }
}

int
main(void)
{
  pid_t my_pid = getpid();
  printf("my pid: %d\n\n", my_pid);

  print_proc_reap_status(my_pid);

  printf("\n");

  /* acquire the reaper status */
  int err = procctl(P_PID, my_pid, PROC_REAP_ACQUIRE, 0);

  if (err == 0) {
    printf("success\n");
  } else if (err == -1) {
    fprintf(stderr, "error\n");
    fprintf(stderr, "%s\n", strerror(errno));
  } else {
    assert(0);
  }

  printf("\n");

  print_proc_reap_status(my_pid);

  printf("\n");

  printf("forking...\n");

  pid_t pid = fork();
  if (pid == -1) {
    fprintf(stderr, "fork failed\n");
    exit(2);
  } else if (pid == 0) {
    printf("I am a child, exec-ing xterm\n");
    execl("/usr/local/bin/xterm", "/usr/local/bin/xterm", (char *)0);
    fprintf(stderr, "exec failed\n");
    exit(2);
  } else {
    printf("I am a my_init, running wait\n");
    for (;;) {
      int status;
      wait(&status);
    }
  }

  return 0;
}