linux-kernel - Re: [PATCH] [v3] y2038: introduce struct __kernel_old

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Message-ID: <CAK8P3a2PApN7arpHa9LUT8sbt-=4AgCOK9X+VSxChBg-=Qrxdg@mail.gmail.com>
Date:   Fri, 16 Mar 2018 09:24:13 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Stultz <john.stultz@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v3] y2038: introduce struct __kernel_old_timeval

On Fri, Mar 16, 2018 at 1:02 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Thu, 15 Mar 2018, Arnd Bergmann wrote:
>> + * legacy timeval structure, only embedded in structures that
>> + * traditionally used 'timeval' to pass time intervals (not absolute
>> + * times). Do not add new users. If user space fails to compile
>> + * here, this is probably because it is not y2038 safe and needs to
>> + * be changed to use another interface.
>> + */
>> +struct __kernel_old_timeval {
>> +     __kernel_long_t tv_sec;
>> +     __kernel_long_t tv_usec;
>> +};
>> +
>> +/*
>>   * The IDs of the various system clocks (for POSIX.1b interval timers):
>>   */
>>  #define CLOCK_REALTIME                       0
>> diff --git a/kernel/time/time.c b/kernel/time/time.c
>> index 5db8f15ec056..6fa99213fc72 100644
>> --- a/kernel/time/time.c
>> +++ b/kernel/time/time.c
>> @@ -486,6 +486,18 @@ struct timeval ns_to_timeval(const s64 nsec)
>>  }
>>  EXPORT_SYMBOL(ns_to_timeval);
>>
>> +struct __kernel_old_timeval ns_to_kernel_old_timeval(const s64 nsec)
>> +{
>> +     struct timespec64 ts = ns_to_timespec64(nsec);
>> +     struct __kernel_old_timeval tv;
>> +
>> +     tv.tv_sec = ts.tv_sec;
>
> We might think about adding some debug aid here which yells when ts.tv_sec
> is > than the cutoff.
>
> Hmm?

We discussed those before (a long time ago) and couldn't really
reach consensus. If we do that, I'd like to have it done consistently
across the kernel, and in a separate patch series.

In particular, we need to decide on a policy for how to handle
it depending on the caller, e.g. do we want to have a way to
WARN_ONCE() for any process calling an unsafe function even
if it doesn't overflow, should we try to return an error to a syscall
when it does overflow, should the behavior be configurable etc.

        Arnd