linux-kernel - Re: [PATCH v2 00/10] posix_clocks: Prepare syscalls for 64 bit time

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Date:   Wed, 29 Nov 2017 22:12:23 +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>,
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Subject: Re: [PATCH v2 00/10] posix_clocks: Prepare syscalls for 64 bit time_t conversion

On Wed, Nov 29, 2017 at 12:17 AM, Deepa Dinamani <deepa.kernel@...il.com> wrote:
> On Tue, Nov 28, 2017 at 6:17 AM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Mon, Nov 27, 2017 at 11:29 PM, Deepa Dinamani <deepa.kernel@...il.com> wrote:
> Right. There are three options:
>
> 1. Use two configs to identify which syscalls need not be supported by
> new architectures.
> In this case it makes sense to say LEGACY_TIME_SYSCALLS and
> COMPAT_32BIT_TIME both need to be disabled for new architectures. And,
> I can reword the config to what you mention below.
>
> 2. Make the LEGACY_TIME_SYSCALLS eliminate non y2038 safe syscalls
> mentioned below only.
> In this case only the native and compat functions of the below
> mentioned syscalls need to be identified by the config. I like this
> option as this clearly identifies which syscalls are deprecated and do
> not have a 64 bit counterpart. Not all architectures need to support
> turning this off.
>
> 3. If we don't need either 1 or 2, then we could stick with what we
> have today in the series as CONFIG_64BIT_TIME will be deleted and they
> only need #ifdef CONFIG_64BIT.
>
> Let me know if anyone prefers something else.

I think I prefer to have both LEGACY_TIME_SYSCALLS to guard
the native deprecated syscalls (disabled on 32-bit architectures after
the conversion, and enabled on 64-bit architectures until
we merge the next one), and COMPAT_32BIT_TIME to guard the
compat versions of both the deprecated and the non-deprecated
syscalls (enabled on all existing 32-bit architectures after the
conversion, and on 64-bit architectures if they provide a compat
mode for the former).

Those two are not symmetric, but I think those are the most
common combinations, and the Kconfig symbol helps document
what they are.

There is one more category for things like io_getevents() and
rt_sigtimedwait that also need two separate compat versions,
one for 32-bit time_t and one for 64-bit time_t, but it seems better
to deal with those case-by-case rather than introducing another
Kconfig symbol.

        Arnd