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

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Date:	Tue, 13 May 2014 11:22:22 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Ley Foon Tan <lftan@...era.com>
CC:	Linux-Arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Chung-Lin Tang <cltang@...esourcery.com>,
	Arnd Bergmann <arnd@...db.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 01/25] asm-generic: Change time_t and clock_t to 64 bit

On 13/05/14 11:17, 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?

Yeh, good point, that won't work.

Cheers
James
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