linux-kernel - Re: [PATCH 01/25] asm-generic: Change time_t and clock

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Date:	Tue, 13 May 2014 12:21:40 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Ley Foon Tan <lftan@...era.com>
Cc:	James Hogan <james.hogan@...tec.com>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Chung-Lin Tang <cltang@...esourcery.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 01/25] asm-generic: Change time_t and clock_t to 64 bit

On Tuesday 13 May 2014 18:17:40 Ley Foon Tan wrote:
> On Tue, May 13, 2014 at 5:50 PM, James Hogan <james.hogan@...tec.com> wrote:
> > Hi,
> >
> > On 13/05/14 10:32, Ley Foon Tan wrote:
> >> On Tue, May 13, 2014 at 5:15 PM, James Hogan <james.hogan@...tec.com> wrote:
> >>> On 13 May 2014 10:02, Ley Foon Tan <lftan@...era.com> wrote:
> >>>>  /*
> >>>> + * Use 64 bit time_t and clock_t as default. 32 bit users can provide an override to
> >>>> + * define these as "long" if needed.
> >>>> + */
> >>>> +#ifndef __kernel_time_t
> >>>> +typedef long long      __kernel_time_t;
> >>>> +#endif
> >>>> +
> >>>> +#ifndef __kernel_clock_t
> >>>> +typedef long long      __kernel_clock_t;
> >>>> +#endif
> >>>
> >>> I think having this as the first patch in the series will break
> >>> bisection for existing 32-bit arches. This needs to be done in such a
> >>> way that at no intermediate commit are __kernel_time_t or
> >>> __kernel_clock_t the wrong size for existing arches, e.g. by having a
> >>> first patch which makes the typedefs conditional but leaves them as
> >>> __kernel_long_t, and a final patch that changes the default after all
> >>> the arches have got their overrides in place.
> >>
> >> Your suggestion is something as below?
> >
> > Yeh, although I like Thomas' idea better, then each existing 32-bit arch
> > can just select the Kconfig symbol to get the smaller type.
> >
> > IIRC Kconfig won't even complain if you select a symbol which doesn't
> > exist yet.
> When we export this posix_types.h file for user software, they need to
> define this config, eg: CONFIG_32BIT_TIME to use 32 bit time. Is this
> what we want to do?

No, this doesn't really work: You can't use CONFIG_* symbols in
user-visible header files.

	Arnd
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