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

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Date:   Fri, 17 Nov 2017 10:31:34 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Deepa Dinamani <deepa.kernel@...il.com>,
        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>,
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        Ingo Molnar <mingo@...hat.com>,
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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 17, 2017 at 9:58 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Fri, 17 Nov 2017, Arnd Bergmann wrote:
>> On Thu, Nov 16, 2017 at 10:04 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> > On Wed, 15 Nov 2017, Deepa Dinamani wrote:
>> >> Would this work for everyone?
>> >
>> > Having extra config switches which are selectable by architectures and
>> > removed when everything is converted is definitely the right way to go.
>> >
>> > That allows you to gradually convert stuff w/o inflicting wreckage all over
>> > the place.
>>
>> The CONFIG_64BIT_TIME would do that nicely for the new stuff like
>> the conditional definition of __kernel_timespec, this one would get
>> removed after we convert all architectures.
>>
>> A second issue is how to control the compilation of the compat syscalls.
>> CONFIG_COMPAT_32BIT_TIME handles that and could be defined
>> in Kconfig as 'def_bool (!64BIT && CONFIG_64BIT_TIME) || COMPAT',
>> this is then just a more readable way of expressing exactly when the
>> functions should be built.
>>
>> For completeness, there may be a third category, depending on how
>> we handle things like sys_nanosleep(): Here, we want the native
>> sys_nanosleep on 64-bit architectures, and compat_sys_nanosleep()
>> to handle the 32-bit time_t variant on both 32-bit and 64-bit targets,
>> but our plan is to not have a native 32-bit sys_nanosleep on 32-bit
>> architectures any more, as new glibc should call clock_nanosleep()
>> with a new syscall number instead. Should we then enclose
>
> Isn't that going to break existing userspace?

No, syscall that existing 32-bit user space enters would be handled by
compat_sys_nanosleep() on both 32-bit and 64-bit kernels at that
point. The idea here is to make the code path more uniform between
32-bit and 64-bit kernels.

      Arnd