linux-kernel - Re: [PATCH 3/4] y2038: time: Introduce struct __kernel_old

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Date:   Wed, 14 Mar 2018 23:02:10 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        Richard Cochran <richardcochran@...il.com>,
        Prarit Bhargava <prarit@...hat.com>,
        Stephen Boyd <stephen.boyd@...aro.org>
Subject: Re: [PATCH 3/4] y2038: time: Introduce struct __kernel_old_timeval

On Sat, Mar 10, 2018 at 9:11 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
>> +extern struct __kernel_old_timeval ns_to_kernel_old_timeval(const s64 nsec);
>
> Generally there's no need to mark arguments with arithmethic types as const, as
> they are never modified in the calling scope.

Sure. Here I just copied from the neighboring line, but that's an obvious
change.

>> + * 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;                 /* seconds */
>> +     __kernel_long_t tv_usec;                /* seconds */
>
> s/seconds/microseconds

Right.

>> +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;
>> +     tv.tv_usec = (suseconds_t) ts.tv_nsec / 1000;
>
> Is ts.tv_nsec guaranteed to never have bits set in the high 32 bits?

Yes, ns_to_timespec64() produces a valid timespec64 structure.

> In any case, the space before the type cast is a bit confusing to me, I think it
> should be written as:
>
>         tv.tv_usec = (suseconds_t)ts.tv_nsec / 1000;
>
> To better show was the higher precedence of the cast is going to result in.

Sure.

Thanks for taking a look, I'll send an updated version.

       Arnd