rem: return EINVAL;
add: return FS_EINVAL;
context: do_seek(int argc, char **argv){    fs_off_t err;    fs_off_t pos;    if (cur_fd < 0) {        printf("no file open! (open or create one with open or make)\n");        return EINVAL;    }        if (argc < 2) {        printf("usage: seek pos\n");        return EINVAL;    }    pos = strtoul(&argv[1][0], NULL, 0);    err = sys_lseek(1, cur_fd, pos, SEEK_SET);    if (err != pos) {        printf("seek to %Ld failed (%Ld)\n", pos, err);    }	return err;}