#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/stat.h>
#include <fcntl.h>

key_t key;

child()
{
	int id = semget(key, 1, IPC_CREAT|SEM_R|SEM_A);
	struct sembuf s;
	s.sem_num = 0;
	s.sem_op = 1;
	s.sem_flg = SEM_UNDO;
	semop(id, &s, 1);
	sleep(5);
	exit(0);
}

main(argc, argv)
	int argc;
	char *argv[];
{
	int pid;
	int id;
	int x;

	key = ftok("/tmp/usema", 0);
	id = semget(key, 1, IPC_CREAT|SEM_R|SEM_A);

	x = semctl(id, 0, GETVAL);
	printf("Oldval %d\n", x);
	pid = fork();
	if (pid == 0) {
		return child();
	}
	wait(&x);
	x = semctl(id, 0, GETVAL);
	printf("Newval %d\n", x);

	/* WITNESS */
}