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

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Date:   Sat, 10 Mar 2018 09:11:23 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        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


> +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.

> + * 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

> +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?

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.

Thanks,

	Ingo