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

[Markus Armbruster]

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.?