Re: [PATCH] ui/gtk: fix UI info precondition

[Marc-André Lureau]

Hi

On Fri, Sep 15, 2023 at 4:46 PM Michael Tokarev <mjt@tls.msk.ru> wrote:
>
> 15.09.2023 14:36, marcandre.lureau@redhat.com:
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> > dpy_get_ui_info() shouldn't be called if the underlying GPU doesn't
> > support it.
> >
> > Before the assert() was added and the regression introduced, GTK code
> > used to get "zero" UI info, for ex with a simple VGA device. The assert
> > was added to prevent from calling when there are no console too. The
> > other display backend that calls dpy_get_ui_info() correctly checks that
> > pre-condition.
> >
> > Calling dpy_set_ui_info() is "safe" in this case, it will simply return
> > an error that can be generally ignored.
> >
> > Fixes: commit a92e7bb4c ("ui: add precondition for dpy_get_ui_info()")
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> >   ui/gtk.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> >
> > diff --git a/ui/gtk.c b/ui/gtk.c
> > index e09f97a86b..7b542da0c0 100644
> > --- a/ui/gtk.c
> > +++ b/ui/gtk.c
> > @@ -726,6 +726,10 @@ static void gd_set_ui_refresh_rate(VirtualConsole *vc, 
> > int refresh_rate)
> >   {
> >       QemuUIInfo info;
> >
> > +    if (!dpy_ui_info_supported(vc->gfx.dcl.con)) {
> > +        return;
> > +    }
> > +
> >       info = *dpy_get_ui_info(vc->gfx.dcl.con);
>
> Current dpy_ui_info_supported():
>
> bool dpy_ui_info_supported(QemuConsole *con)
> {
>      if (con == NULL) {
>          con = active_console;
>      }
>      if (con == NULL) {
>          return false;
>      }
>
>      return con->hw_ops->ui_info != NULL;
> }
>
> This whole thing smells a bit wrong.  I'm not saying it *is* wrong, but
> the feeling is here.
>
> Where dpy_ui_info_supported() is called with a NULL con, so that an "active"
> console needs to be used instead?
>
> Maybe we should instead use something like
>
>     if (!vc->gfx.dcl.con)
>
> here in gd_set_ui_refresh_rate() ?
>
> At the very least, the code is a bit, well, confusing.

I agree it's a bit confusing to have dpy_*() functions accept NULL
arguments to mean "active_console". I don't really have a good idea
what to do else. Just having "if (!vc->gfx.dcl.con)" is not quite
enough though, as we shouldn't get_ui_info() if it's not supported
(there are no errors returned then, just "invalid/zero" values).

-- 
Marc-André Lureau