utf8_casefold
dlen = utf8_casefold(um, &qstr, buff, PATH_MAX);
len = utf8_casefold(dir->i_sb->s_encoding, iname, buf, EXT4_NAME_LEN);
len = utf8_casefold(sb->s_encoding, fname->usr_fname,
cf_len = utf8_casefold(rdd->map, &qstr, cf_name, NAME_MAX);
cf_len = utf8_casefold(um, &q_name, cf_name,
EXPORT_SYMBOL(utf8_casefold);
int utf8_casefold(const struct unicode_map *um, const struct qstr *str,