Re: [Xen-devel] [RFC PATCH v2 04/11] time: Add rtc_time_to_tm64() safe version(using time64_t)

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Thu, 30 Oct 2014, pang.xunlei wrote:

As you can guess already: $subject sucks.

> +
>  /*
>   * Convert seconds since 01-01-1970 00:00:00 to Gregorian date.
> + * Safe version for 2038 safety.

See previous replies.

>   */
> -void rtc_time_to_tm(unsigned long time, struct rtc_time *tm)
> +void rtc_time_to_tm64(time64_t time, struct rtc_time *tm)

What's tm64? 

This function is converting time64 to rtc_time. So the proper function
name is: rtc_time64_to_tm

Can you see the difference?

>  {
>       unsigned int month, year;
>       int days;
>  
> -     days = time / 86400;
> +     days = div_s64(time, 86400);
>       time -= (unsigned int) days * 86400;
>  
>       /* day of the week, 1970-01-01 was a Thursday */
> @@ -81,13 +83,23 @@ void rtc_time_to_tm(unsigned long time, struct rtc_time 
> *tm)
>       tm->tm_mon = month;
>       tm->tm_mday = days + 1;
>  
> -     tm->tm_hour = time / 3600;
> +     tm->tm_hour = div_s64(time, 3600);

We already adjusted time to a value which is less than 24 * 3600,
i.e. it fits nicely into a long on 32bit. So we can avoid the whole
div_s64 business and simply do:

        unsigned int month, year;
+       unsigned long secs;
        int days;

-       days = time / 86400;
-       time -= (unsigned int) days * 86400;
+       days = div_s64(time, 86400);
+       secs = time - (unsigned int) days * 86400;

And change the rest which uses time to:

-       tm->tm_hour = time / 3600;
+       tm->tm_hour = secs / 3600;

Sigh.

        tglx

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