linux-kernel - Re: [PATCH] lib/atomic64_test: do not build on non-atomic64 systems

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Date:	Thu, 21 Oct 2010 16:24:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mike Frysinger <vapier@...too.org>
Cc:	Luca Barbieri <luca@...a-barbieri.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/atomic64_test: do not build on non-atomic64 systems

On Thu, 21 Oct 2010 19:04:36 -0400
Mike Frysinger <vapier@...too.org> wrote:

> On Thu, Oct 21, 2010 at 18:55, Andrew Morton wrote:
> > On Thu, 21 Oct 2010 18:23:37 -0400 Mike Frysinger wrote:
> >> On Thursday, October 21, 2010 18:02:50 Andrew Morton wrote:
> >> > On Sat, 16 Oct 2010 13:27:15 -0400 Mike Frysinger wrote:
> >> > > If the arch doesn't provide atomic64 functionality (there are quite a
> >> > > few), then don't bother trying to build this test.
> >> >
> >> > I don't get it. __If the arch doesn't implement atomic64 then this file
> >> > will get zillions of build errors, won't it?
> >>
> >> ... which is why i added the ifdef protection
> >
> > So the changelog was poor. __Please write complete changelogs so I need
> > to have this sort of conversation less often?
> 
> the changelog seems pretty clear to me.  arch doesnt provide atomic64,
> so dont build code that uses atomic64.

That the patch fixes build errors is rather important information.

> > I know that. __But the standard way for an architecture to indicate to
> > the core that it impements a feature is for it to define CONFIG_HAVE_*.
> > Picking some related #define which architectures happen to implement
> > is atypical and unexpected.
> >
> > Will it cause problems? __Probably not, unless the arch goes and defines
> > ATOMIC64_INIT without actually implementing atomic64. __But it's
> > atypical and unexpected and, yes, lazy!
> 
> you can say "lazy" all you like.  i dont see the point in going that route.

Try

	grep HAVE arch/x86/Kconfig

If all of those were instead to use some random #define which the
particular feature happened to define in some header file then we would
have a mess on our hands.

There's your point.
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