Re: [RFC PATCH v2 02/11] time: Add mktime64() safe version(using time64_t)

From: Thomas Gleixner
Date: Thu Oct 30 2014 - 09:44:09 EST


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

Same problem with the $subject as in the previous patch.

> As part of addressing 2038 saftey for in-kernel uses, this patch

s/saftey/safety/

saftey is something completely different.

> +/*
> + * Converts Gregorian date to seconds since 1970-01-01 00:00:00.
> + * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
> + * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
> + *
> + * [For the Julian calendar (which was used in Russia before 1917,
> + * Britain & colonies before 1752, anywhere else before 1582,
> + * and is still in use by some communities) leave out the
> + * -year/100+year/400 terms, and add 10.]
> + *
> + * This algorithm was first published by Gauss (I think).
> + *

So this blindly copies the comment from mktime but misses to add a
proper docbook comment for the function.

> + * Safe version 2038 safety on 32-bit systems.

This sentence makes no sense at all. Aside of that you want to do the
same as I suggested for do_settimeofday64

* mktime64 - Convert gregrorian date to seconds since 1970. y2038 safe

> + */
> +time64_t
> +mktime64(const unsigned int year0, const unsigned int mon0,
> + const unsigned int day, const unsigned int hour,
> + const unsigned int min, const unsigned int sec)

Make this

time64_t mktime64(const unsigned int year0, const unsigned int mon0,
const unsigned int day, const unsigned int hour,
const unsigned int min, const unsigned int sec)

please.

> +{
> + time64_t ret;
> + unsigned int mon = mon0, year = year0;

I pretty much prefer the following style:

+ unsigned int mon = mon0, year = year0;
+ time64_t ret;

Way simpler to parse.


> + /* 1..12 -> 11,12,1..10 */
> + if (0 >= (int) (mon -= 2)) {
> + mon += 12; /* Puts Feb last since it has leap day */

Please get rid of the tail comments while you are at it:

/* Put Feb last since it has a leap day */
mon += 12;

Again simpler to parse.

> + year -= 1;
> + }
> +
> + ret = (year/4 - year/100 + year/400 + 367*mon/12 + day) + year*365 - 719499;

For readability sake

> + ret = ret*24 + hour; /* now have hours */

Please kill these pointless comments. The calculation above is the one
which could do with a comment not the obvious days to hrs and hrs to
min and min to sec conversions.

We do not blindly copy code and leave the mess unchanged.

> + ret = ret*60 + min; /* now have minutes */
> + ret = ret*60 + sec; /* finally seconds */
> +
> + return ret;
> +}
> +
> +EXPORT_SYMBOL(mktime64);

EXPORT_SYMBOL_GPL please.

> +
> /* Converts Gregorian date to seconds since 1970-01-01 00:00:00.
> * Assumes input in normal date format, i.e. 1980-12-31 23:59:59
> * => year=1980, mon=12, day=31, hour=23, min=59, sec=59.
> @@ -318,6 +356,7 @@ EXPORT_SYMBOL(timespec_trunc);
> * WARNING: this function will overflow on 2106-02-07 06:28:16 on
> * machines where long is 32-bit! (However, as time_t is signed, we
> * will already get problems at other places on 2038-01-19 03:14:08)
> + * TODO: [2038 safety] should be replaced by mktime64().
> */
> unsigned long
> mktime(const unsigned int year0, const unsigned int mon0,

Why are you keeping this implementation instead of replacing the
comment by a simple one liner

/*
* mktime - Convert gregrorian date to seconds since 1970. Deprecated. Use mktime64
*/

No need to add a full docbook comment as this is going away anyway.

and change the implementation to

{
return mktime64(....);
}

Thanks,

tglx
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/