print_pollfd
printf("rpipe p[0]="); print_pollfd(&p[0]); putchar('\n');
printf("wpipe p[1]="); print_pollfd(&p[1]); putchar('\n');
printf("rpipe p[0]="); print_pollfd(&p[0]); putchar('\n');
printf("zero p[0]="); print_pollfd(&p[0]); putchar('\n');
printf("null p[1]="); print_pollfd(&p[1]); putchar('\n');
printf("zero p[0]="); print_pollfd(&p[0]); putchar('\n');
printf("null p[1]="); print_pollfd(&p[1]); putchar('\n');