linux-kernel - Re: [Intel-gfx] [PATCH 11/12] sched: use for_each

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Date:   Wed, 11 Jul 2018 17:51:03 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Daniel Vetter <daniel@...ll.ch>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Subject: Re: [Intel-gfx] [PATCH 11/12] sched: use for_each_if in topology.h

On Mon, Jul 09, 2018 at 07:55:20PM +0200, Daniel Vetter wrote:
> On Mon, Jul 9, 2018 at 6:12 PM, Mark Rutland <mark.rutland@....com> wrote:
> > On Mon, Jul 09, 2018 at 06:03:42PM +0200, Peter Zijlstra wrote:
> >> On Mon, Jul 09, 2018 at 05:52:04PM +0200, Daniel Vetter wrote:
> >> > for_each_something(foo)
> >> >     if (foo->bla)
> >> >             call_bla(foo);
> >> >     else
> >> >             call_default(foo);
> >> >
> >> > Totally contrived, but this complains. Liberally sprinkling {} also shuts
> >> > up the compiler, but it's a bit confusing given that a plain for {;;} is
> >> > totally fine. And it's confusing since at first glance the compiler
> >> > complaining about nested if and ambigous else doesn't make sense since
> >> > clearly there's only 1 if there.
> >>
> >> Ah, so the pattern the compiler tries to warn about is:
> >>
> >>       if (foo)
> >>               if (bar)
> >>                       /* stmts1 */
> >>               else
> >>                       /* stmts2 *
> >>
> >> Because it might not be immediately obvious with which if the else goes.
> >> Which is fair enough I suppose.
> >>
> >> OK, ACK.
> >
> > Just to bikeshed, there could be macros other than for_each_*() macros
> > that will want to use this internally, so perhaps it would be worth the
> > generic version being named something like if_noelse().
> >
> > We could always add that as/when required, though.
> 
> I think a better name would be really good, but both when we added it
> for i915 and when we move it to drm headers we drew a blank.
> if_noelse() describes pretty good what it does, but kinda fails on the
> "where should I use it" departement. If there's some consensus I can
> sed the patches quickly.

Just to be clear: for_each_if() is fine by me, so no need to change
things.

Sorry for the noise!

Mark.