Re: [PATCH v2] ui/gtk: Allow user to select monitor number to display qemu in full screen through new gtk display option

[Markus Armbruster <armbru@redhat.com>]

Gerd Hoffmann <kraxel@redhat.com> writes:


[...]

>> sweeaun: Based on my observation, when specific monitor device disconnected after QEMU launched on it, QEMU application will not be visible but QEMU application still running and screen framebuffer size is not being changed at all. QEMU application will be visible once you connect back the monitor. 
>
> Well, that probably depends on the display server and might even be
> configurable.  I've seen different ways to handle that, most common ones
> being (a) do nothing or (b) trying move all windows to the monitor which
> is still connected.
>
> I don't think qemu has to worry much here, and trying to automatically
> adapt to hot-plugged monitors might even have bad interactions with
> whatever the display server is going to do.

I'm concerned there is a TOCTTOU issue:

    if (opts->u.gtk.has_monitor) {
        int n_monitor;
1.      n_monitor = gdk_display_get_n_monitors(window_display);

2.      if ((opts->u.gtk.monitor <= n_monitor) &&
            (opts->u.gtk.monitor > 0)) {
            GdkScreen *gdk_screen;
            gdk_screen = gdk_display_get_default_screen(window_display);
3.          gtk_window_fullscreen_on_monitor(GTK_WINDOW(s->window), gdk_screen,
                                             (opts->u.gtk.monitor - 1));
        } else {
            fprintf(stderr, "Invalid GTK monitor argument\n");
        }
    }

If monitors can go at any time, then the check 2. cannot ensure we pass
a valid monitor number at 3.

I asked what happens when we pass an invalid monitor number.  I'm not
sure I understand sweeaun's answer.

If what happens is sane, then why have check 2.?