linux-kernel - Re: [PATCH RFC 05/12] time: Convert rtc_tm_to_time_unsafe() to rtc_tm_to_time() in rtc

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Date:	Mon, 27 Oct 2014 23:03:01 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"pang.xunlei" <pang.xunlei@...aro.org>
cc:	linux-kernel@...r.kernel.org, rtc-linux@...glegroups.com,
	John Stultz <john.stultz@...aro.org>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH RFC 05/12] time: Convert rtc_tm_to_time_unsafe() to
 rtc_tm_to_time() in rtc_hctosys()

On Mon, 27 Oct 2014, pang.xunlei wrote:
> The kernel uses 32-bit signed value(time_t) for seconds since 1970-01-01:00:00:00, so it
> will overflow at 2038-01-19 03:14:08 on 32-bit systems. We call this "2038 safety" issue.

We really know that by now. No need to repeat that for every patch. 
 
> As part of addressing 2038 saftey for in-kernel uses, this patch creates no functional change
> in existing users, and converts rtc_tm_to_time_unsafe() to rtc_tm_to_time() in rtc_hctosys().

Please line break your changelogs properly. That's how it should look
like:

> As part of addressing 2038 saftey for in-kernel uses, this patch
> creates no functional change in existing users, and converts
> rtc_tm_to_time_unsafe() to rtc_tm_to_time() in rtc_hctosys().
 
Can you spot the difference?

> @@ -26,9 +26,10 @@ static int __init rtc_hctosys(void)
>  {
>  	int err = -ENODEV;
>  	struct rtc_time tm;
> -	struct timespec tv = {
> +	struct timespec64 tv = {
>  		.tv_nsec = NSEC_PER_SEC >> 1,
>  	};
> +	struct timespec ts32;

So this is exactly why I dislike this whole flag day conversion
thing. If you add

       rtc_tm_to_time64()
       do_settimeofday64()

in the first place, you can convert the whole function in one go
without introducing intermediate variables which then need to be
undone later again.

Thanks,

	tglx
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