rem: st.st_size = new_size;
add: st.size = new_size;
context: do_trunc(int argc, char **argv){    int             err, new_size;    char            fname[256];    struct my_stat  st;    strcpy(fname, "/myfs/");    if (argc < 3) {        printf("usage: trunc fname newsize\n");        return EINVAL;    }    strcat(fname, argv[1]);    new_size = strtoul(argv[2], NULL, 0);    st.st_size = new_size;    err = sys_wstat(1, -1, fname, &st, WSTAT_SIZE, 0);    if (err != 0) {        printf("truncate to %d bytes failed for %s\n", new_size, fname);    }    return err;}