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

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Date:   Wed, 15 Nov 2017 15:11:31 -0800
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
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>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        oberpar@...ux.vnet.ibm.com, oprofile-list@...ts.sf.net,
        Paul Mackerras <paulus@...ba.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Robert Richter <rric@...nel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        sebott@...ux.vnet.ibm.com, sparclinux <sparclinux@...r.kernel.org>,
        Stefan Haberland <sth@...ux.vnet.ibm.com>,
        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

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

Thanks, I think you are right. I had the check conditional on
CONFIG_64BIT_TIME and then removed as I forgot why I added it. :)

> 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?

Another approach would be to use separate configs:

1. To indicate 64 bit time_t syscall support. This will be dependent
on architectures as CONFIG_64BIT_TIME.
We can delete this once all architectures have provided support for this.

2. Another config (maybe COMPAT_32BIT_TIME?) to be introduced later,
which will compile out all syscalls/ features that use 32 bit time_t.
This can help build a y2038 safe kernel later.

Would this work for everyone?

-Deepa