void usage()
{
    std::cerr << "Usage: " << whoami << " {read|write} {large|small} outfile"
              << std::endl;
    exit(2);
}
void usage()
{
    std::cerr << "Usage: " << whoami << " {read|write} {large|small} outfile"
              << std::endl;
    exit(2);
}