linux-kernel - Re: [PATCH 6/6] cputime: Introduce cputime_to_timespec64()/timespec64_to

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Date:	Fri, 17 Jul 2015 16:39:32 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	benh@...nel.crashing.org, Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>, peterz@...radead.org,
	paulus@...ba.org, mpe@...erman.id.au, schwidefsky@...ibm.com,
	heiko.carstens@...ibm.com, linux390@...ibm.com, rth@...ddle.net,
	riel@...hat.com, cl@...ux.com, tj@...nel.org,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-arch@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	y2038 Mailman List <y2038@...ts.linaro.org>
Subject: Re: [PATCH 6/6] cputime: Introduce cputime_to_timespec64()/timespec64_to_cputime()

On 16 July 2015 at 18:43, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Thu, 16 Jul 2015, Baolin Wang wrote:
>> On 15 July 2015 at 19:55, Thomas Gleixner <tglx@...utronix.de> wrote:
>> > On Wed, 15 Jul 2015, Baolin Wang wrote:
>> >
>> >> On 15 July 2015 at 18:31, Thomas Gleixner <tglx@...utronix.de> wrote:
>> >> > On Wed, 15 Jul 2015, Baolin Wang wrote:
>> >> >
>> >> >> The cputime_to_timespec() and timespec_to_cputime() functions are
>> >> >> not year 2038 safe on 32bit systems due to that the struct timepsec
>> >> >> will overflow in 2038 year.
>> >> >
>> >> > And how is this relevant? cputime is not based on wall clock time at
>> >> > all. So what has 2038 to do with cputime?
>> >> >
>> >> > We want proper explanations WHY we need such a change.
>> >>
>> >> When converting the posix-cpu-timers, it call the
>> >> cputime_to_timespec() function. Thus it need a conversion for this
>> >> function.
>> >
>> > There is no requirement to convert posix-cpu-timers on their own. We
>> > need to adopt the posix cpu timers code because it shares syscalls
>> > with the other posix timers, but that still does not explain why we
>> > need these functions.
>> >
>>
>> In posix-cpu-timers, it also defined some 'k_clock struct' variables,
>> and we need to convert the callbacks of the 'k_clock struct' which are
>> not year 2038 safe on 32bit systems. Some callbacks which need to
>> convert call the cputime_to_timespec() function, thus we also want to
>> convert the cputime_to_timespec() function to a year 2038 safe
>> function to make all them ready for the year 2038 issue.
>
> You are not getting it at all.
>
> 1) We need to change k_clock callbacks due to 2038 issues
>
> 2) posix cpu timers implement affected callbacks
>
> 3) posix cpu timers themself and cputime are NOT affected by 2038
>
> So we have 2 options to change the code in posix cpu timers:
>
>    A) Do the timespec/timespec64 conversion in the posix cpu timer
>       callbacks and leave the cputime functions untouched.
>
>    B) Implement cputime/timespec64 functions to avoid #A
>
>    If you go for #B, you need to provide a reasonable explanation why
>    it is better than #A. And that explanation has absolutely nothing
>    to do with 2038 safety.

Very thanks for your explanation, and I'll think about that.

>
> Not everything is a 2038 issue, just because the only tool you have is
> a timespec64.
>
> Thanks,
>
>         tglx
>
>
>



-- 
Baolin.wang
Best Regards
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