static int remove_dir(const char *dirname)
{
    DIR *dir;
    struct dirent *entry;
    char path[PATH_MAX];

    dir = opendir(dirname);
    if (dir == NULL) {
        LOGE("opendir %s failed\n", dirname);
        return -1;
    }

    while ((entry = readdir(dir)) != NULL) {
        if (strcmp(entry->d_name, ".") && strcmp(entry->d_name, "..")) {
            snprintf(path, (size_t) PATH_MAX, "%s/%s", dirname, entry->d_name);
            if (entry->d_type == DT_DIR) {
                remove_dir(path);
            } else {
                // delete file
                unlink(path);
            }
        }
    }
    closedir(dir);

    // now we can delete the empty dir
    rmdir(dirname);
    return 0;
}