linux-kernel - Re: [PATCH 0/9] posix_clocks: Prepare syscalls for 64 bit time

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Date:   Tue, 14 Nov 2017 15:24:40 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Deepa Dinamani <deepa.kernel@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Chris Metcalf <cmetcalf@...lanox.com>, cohuck@...hat.com,
        David Miller <davem@...emloft.net>,
        Helge Deller <deller@....de>, devel@...verdev.osuosl.org,
        gerald.schaefer@...ibm.com, gregkh <gregkh@...uxfoundation.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Jan Hoeppner <hoeppner@...ux.vnet.ibm.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Julian Wiedmann <jwi@...ux.vnet.ibm.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        "open list:RALINK MIPS ARCHITECTURE" <linux-mips@...ux-mips.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
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        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
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        Martin Schwidefsky <schwidefsky@...ibm.com>,
        sebott@...ux.vnet.ibm.com, sparclinux <sparclinux@...r.kernel.org>,
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        Ursula Braun <ubraun@...ux.vnet.ibm.com>,
        Will Deacon <will.deacon@....com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH 0/9] posix_clocks: Prepare syscalls for 64 bit time_t conversion

On Fri, Nov 10, 2017 at 11:42 PM, Deepa Dinamani <deepa.kernel@...il.com> wrote:
> The series is a preparation series for individual architectures
> to use 64 bit time_t syscalls in compat and 32 bit emulation modes.
>
> This is a follow up to the series Arnd Bergmann posted:
> https://sourceware.org/ml/libc-alpha/2015-05/msg00070.html
>
> Big picture is as per the lwn article:
> https://lwn.net/Articles/643234/
>
> The series is directed at converting posix clock syscalls:
> clock_gettime, clock_settime, clock_getres and clock_nanosleep
> to use a new data structure __kernel_timespec at syscall boundaries.
> __kernel_timespec maintains 64 bit time_t across all execution modes.
>
> vdso will be handled as part of each architecture when they enable
> support for 64 bit time_t.
>
> The compat syscalls are repurposed to provide backward compatibility
> by using them as native syscalls as well for 32 bit architectures.
> They will continue to use timespec at syscall boundaries.
>
> CONFIG_64_BIT_TIME controls whether the syscalls use __kernel_timespec
> or timespec at syscall boundaries.
>
> The series does the following:
> 1. Enable compat syscalls unconditionally.
> 2. Add a new __kernel_timespec type to be used as the data structure
>    for all the new syscalls.
> 3. Add new config CONFIG_64BIT_TIME(intead of the CONFIG_COMPAT_TIME in
>    [1] and [2] to switch to new definition of __kernel_timespec. It is
>    the same as struct timespec otherwise.
>
> Arnd Bergmann (1):
>   y2038: introduce CONFIG_64BIT_TIME

The series looks good to me overall, and I've added it to my build-testing tree
to see if it shows any regressions in random configurations.

I had on concern about x32, maybe we should check
for "COMPAT_USE_64BIT_TIME" before zeroing out the tv_nsec
bits.

Regarding CONFIG_COMPAT_TIME/CONFIG_64BIT_TIME, would
it help to just leave out that part for now and unconditionally
define '__kernel_timespec' as 'timespec' until we are ready to
convert the architectures?

       Arnd