Comment 2 for bug 1122386

Rather than adding:

class mir::DisplayServerInstance and
mir::DisplayServerInstance::run(int argc, char **argv, std::function<void(mir::DisplayServer *)> server_ready)

I'd suggest the configuration object deals with the command line. Vis:

mir::DefaultServerConfiguration::DefaultServerConfiguration(int argc, char const**argv);

If a callback is needed, then why not add that to DisplayServer::start()?