Re: [PATCH net-next] tcp: Fix tcp_syn_flood_action() if CONFIG_IPV6=n

[Jamie Bainbridge]

On Thu, 17 Nov 2022 at 08:15, Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Thu, 17 Nov 2022 08:39:43 +1100 Jamie Bainbridge wrote:
> > >         if (v6) {
> > > #ifdef v6
> > >                 expensive_call6();
> > > #endif
> > >         } else {
> > >                 expensive_call6();
> > >         }
> >
> > These should work, but I expect they cause a comparison which can't be
> > optimised out at compile time. This is probably why the first style
> > exists.
> >
> > In this SYN flood codepath optimisation doesn't matter because we're
> > doing ratelimited logging anyway. But if we're breaking with existing
> > style, then wouldn't the others also have to change to this style? I
> > haven't reviewed all the other usage to tell if they're in an oft-used
> > fastpath where such a thing might matter.
>
> I think the word style already implies subjectivity.

You are right. Looking further, there are many other ways
IF_ENABLED(CONFIG_IPV6) is used, including similar to the ways you
have suggested.

I don't mind Geert's original patch, but if you want a different
style, I like your suggestion with v4 first:

        if (v4) {
                expensive_call4();
#ifdef v6
        } else {
                expensive_call6();
#endif
        }

Jamie