//shm/incr_dev_zero.c
int
main(int argc, char **argv)
{
	int		fd, i, nloop;
	int		*ptr;
	sem_t	*mutex;

	if (argc != 2)
		err_quit("usage: incr_dev_zero <#loops>");
	nloop = atoi(argv[1]);

		/*  /dev/zero     */
	fd = Open("/dev/zero", O_RDWR);
	ptr = Mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	Close(fd);
