rem: return EINVAL;
add: return FS_EINVAL;
context: do_fcntl(int argc, char **argv){	int err;    if (cur_fd < 0) {        printf("no file open! (open or create one with open or make)\n");        return EINVAL;    }	if (argc < 2) {		printf("fcntl: too few arguments\n");		return EINVAL;	}	err = sys_ioctl(1, cur_fd, atoi(argv[1]), 0, 0);	if (err < 0) {	    printf("fcntl: error!\n");	}	return err;}