rem: return EINVAL;
add: return FS_EINVAL;
context: do_remove_attr(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("usage: rmattr <attribute name>\n");		return EINVAL;	}    err = sys_remove_attr(1, cur_fd, argv[1]);    printf("remove_attr returned %d\n", err);	return err;}