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

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Date:   Mon, 9 Jul 2018 19:55:20 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Mark Rutland <mark.rutland@....com>
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 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.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch