Code review comment for lp:~fourdollars/unity-greeter/add-hidpi-support

Looking at unity-settings-daemon/gnome-settings-daemon/main.c

static void
name_acquired_handler (GDBusConnection *connection,
                       const gchar *name,
                       gpointer user_data)
{
        GDBusProxy *proxy;

        proxy = gnome_settings_session_get_session_proxy ();
#ifdef HAVE_IBUS
        set_legacy_ibus_env_vars (proxy);
#endif
        start_settings_manager ();
        register_with_gnome_session (proxy);
        watch_for_term_signal (manager);
}

And in unity-greeter/src/settings-daemon.vala:

[DBus (name="org.gnome.SessionManager")]
public class SessionManagerInterface : Object
{
    public bool session_is_active { get { return true; } }
    public string session_name { get { return "ubuntu"; } }
    public uint32 inhibited_actions { get { return 0; } }
}

So I think you should be able to add a register_client method and wait for "gnome-settings-daemon" to connect.