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Date:   Tue, 28 Nov 2017 15:17:54 -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 v2 00/10] posix_clocks: Prepare syscalls for 64 bit time_t conversion

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:
>>>> I decided against using LEGACY_TIME_SYSCALLS to conditionally compile
>>>> legacy time syscalls such as sys_nanosleep because this will need to
>>>> enclose compat_sys_nanosleep as well. So, defining it as
>>>>
>>>> config LEGACY_TIME_SYSCALLS
>>>>      def_bool 64BIT || !64BIT_TIME
>>>>
>>>> will not include compat_sys_nanosleep. We will instead need a new config to
>>>> exclusively mark legacy syscalls.
>>>
>>> Do you mean we would need to do this separately for native and compat
>>> syscalls, and have yet another option, like LEGACY_TIME_SYSCALLS
>>> and LEGACY_TIME_COMPAT_SYSCALLS, to cover all cases? I would
>>> think that CONFIG_COMPAT_32BIT_TIME handles all the compat versions,
>>> while CONFIG_LEGACY_TIME_SYSCALLS handles all the native ones.
>>
>> I meant sys_nanosleep would be covered by LEGACY_TIME_SYSCALLS, but
>> compat_sys_nanosleep would be covered by CONFIG_COMPAT_32BIT_TIME
>> along with other compat syscalls.
>> So, if we define the LEGACY_TIME_SYSCALLS as
>>
>>
>>         "This controls the compilation of the following system calls:
>>         time, stime, gettimeofday, settimeofday, adjtimex, nanosleep,
>> alarm, getitimer,
>>         setitimer, select, utime, utimes, futimesat, and
>> {old,new}{l,f,}stat{,64}.
>>         These all pass 32-bit time_t arguments on 32-bit architectures and
>>         are replaced by other interfaces (e.g. posix timers and clocks, statx).
>>         C libraries implementing 64-bit time_t in 32-bit architectures have to
>>         implement the handles by wrapping around the newer interfaces.
>>         New architectures should not explicitly enable this."
>>
>> This would not be really true as compat interfaces have nothing to do
>> with this config.
>>
>> I was proposing that we could have LEGACY_TIME_SYSCALLS config, but
>> then have all these "deprecated" syscalls be enclosed within this,
>> compat or not.
>> This will also mean that we will have to come up representing these
>> syscalls in the syscall header files.
>> This can be a separate patch and this series can be merged as is if
>> everyone agrees.
>
> I think doing this separately  would be good, I don't see any interdependency
> with the other patches, we just need to decide what we want in the long
> run.

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 agree my text that you cited doesn't capture the situation correctly,
> as this is really about the obsolete system calls that take 64-bit time_t
> arguments on architectures that are converted to allow 64-bit time_t
> for non-obsolete system calls.
>
> Maybe it's better to just reword this to
>
>       "This controls the compilation of the following system calls:
>       time, stime, gettimeofday, settimeofday, adjtimex, nanosleep,
> alarm, getitimer,
>       setitimer, select, utime, utimes, futimesat, and {old,new}{l,f,}stat{,64}.
>       These are all replaced by other interfaces (e.g. posix timers and clocks,
>       statx) on architectures that got converted from 32-bit time_t to
> 64-bit time_t.
>       C libraries implementing 64-bit time_t in 32-bit architectures have to
>       implement the handles by wrapping around the newer interfaces.
>       New architectures should not explicitly enable this."
>
> That would clarify that it's not about the compat system calls, while
> also allowing the two options to be set independently.

-Deepa

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