Date:	Wed, 15 Jul 2009 08:59:53 +0800
From:	Zhaolei <zhaolei@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	mingo@...e.hu, tglx@...utronix.de, hirofumi@...l.parknet.co.jp,
	linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH 1/2] Add function to convert between calendar time
 and broken-down time for universal use

Andrew Morton wrote:
> On Tue, 14 Jul 2009 16:03:12 +0800
> Zhaolei <zhaolei@...fujitsu.com> wrote:
>
>   
>> There are many similar code in kernel for one object:
>> convert time between calendar time and broken-down time.
>>
>> Here is some source I found:
>> fs/ncpfs/dir.c
>> fs/smbfs/proc.c
>> fs/fat/misc.c
>> fs/udf/udftime.c
>> fs/cifs/netmisc.c
>> net/netfilter/xt_time.c
>> drivers/scsi/ips.c
>> drivers/input/misc/hp_sdc_rtc.c
>> drivers/rtc/rtc-lib.c
>> arch/ia64/hp/sim/boot/fw-emu.c
>> arch/m68k/mac/misc.c
>> arch/powerpc/kernel/time.c
>> arch/parisc/include/asm/rtc.h
>> ...
>>
>> We can make a common function for this type of conversion,
>> At least we can get following benefit:
>> 1: Make kernel simple and unify
>> 2: Easy to fix bug in converting code
>> 3: Reduce clone of code in future
>>    For example, I'm trying to make ftrace display walltime,
>>    this patch will make me easy.
>>
>>     
>
> The objective is a good one.  Have you verified that these new library
> functions can be used by most/all of the above callers?
>   

Hello, Andrew

Thanks for your review.

I checked some of them, and I think this new library can make them simple.
A example is my patch for fs/fat/misc.c.

>   
>> Signed-off-by: Zhao Lei <zhaolei@...fujitsu.com>
>> ---
>>  include/linux/time.h   |    9 +++
>>  kernel/time/Makefile   |    2 +-
>>  kernel/time/timeconv.c |  180 
>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 190 insertions(+), 1 deletions(-)
>>  create mode 100644 kernel/time/timeconv.c
>>
>> diff --git a/include/linux/time.h b/include/linux/time.h
>> index ea16c1a..0ae0e6e 100644
>> --- a/include/linux/time.h
>> +++ b/include/linux/time.h
>> @@ -151,6 +151,15 @@ extern void update_xtime_cache(u64 nsec);
>>  struct tms;
>>  extern void do_sys_times(struct tms *);
>>  
>> +extern void gmtime(__kernel_time_t totalsecs,
>> +        unsigned int *year, unsigned int *mon, unsigned int *mday,
>> +        unsigned int *hour, unsigned int *min, unsigned int *sec,
>> +        unsigned int *wday, unsigned int *yday);
>> +extern void localtime(__kernel_time_t totalsecs,
>> +        unsigned int *year, unsigned int *mon, unsigned int *mday,
>> +        unsigned int *hour, unsigned int *min, unsigned int *sec,
>> +        unsigned int *wday, unsigned int *yday);
>>     
>
> I'd imagine that many callers would at least need some types changed -
> replace `int' with `unsigned int', etc.  Not a big problem.
>   

Actually, I considered to use int instead, but at last I use unsigned int to
make it same with mktime() which is already in kernel.

>   
>>  /**
>>   * timespec_to_ns - Convert timespec to nanoseconds
>>   * @ts:        pointer to the timespec variable to be converted
>> diff --git a/kernel/time/Makefile b/kernel/time/Makefile
>> index 0b0a636..ee26662 100644
>> --- a/kernel/time/Makefile
>> +++ b/kernel/time/Makefile
>> @@ -1,4 +1,4 @@
>> -obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o 
>> timecompare.o
>> +obj-y += timekeeping.o ntp.o clocksource.o jiffies.o timer_list.o 
>> timecompare.o timeconv.o
>>  
>>  obj-$(CONFIG_GENERIC_CLOCKEVENTS_BUILD)        += clockevents.o
>>  obj-$(CONFIG_GENERIC_CLOCKEVENTS)        += tick-common.o
>> diff --git a/kernel/time/timeconv.c b/kernel/time/timeconv.c
>> new file mode 100644
>> index 0000000..c710605
>> --- /dev/null
>> +++ b/kernel/time/timeconv.c
>> @@ -0,0 +1,180 @@
>> +/*
>> + * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, 
>> Inc.
>>     
>
> The patch is significantly wordwrapped by your email client.
>
> The patch has no tabs in it at all - either some serious cleanup is
> needed of your email client is performing tab-to-space conversion.
>   

Sorry...I reinstalled a email client......
I'll fix it and resend this patch.


>> + * This file is part of the GNU C Library.
>> + * Contributed by Paul Eggert (eggert@...nsun.com).
>> + *
>> + * The GNU C Library is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU Library General Public License as
>> + * published by the Free Software Foundation; either version 2 of the
>> + * License, or (at your option) any later version.
>> + *
>> + * The GNU C Library is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * Library General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU Library General Public
>> + * License along with the GNU C Library; see the file COPYING.LIB.  If not,
>> + * write to the Free Software Foundation, Inc., 59 Temple Place - Suite 
>> 330,
>> + * Boston, MA 02111-1307, USA.
>> + */
>> +
>> +/*
>> + * Converts the calendar time to broken-down time representation
>> + * Based on code from glibc-2.6
>> + *
>> + * 2009-7-14:
>> + *   Moved from glibc-2.6 to kernel by Zhaolei<zhaolei@...fujitsu.com>
>> + */
>> +
>> +#include <linux/time.h>
>> +#include <linux/module.h>
>> +
>> +/*
>> + * Nonzero if YEAR is a leap year (every 4 years,
>> + * except every 100th isn't, and every 400th is).
>> + */
>> +static inline int __isleap(unsigned int year)
>> +{
>> +    return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
>> +}
>>     
>
> The explicit `inline' probably isn't beneficial here.
>   

OK, I'll remove it.

>   
>> +/* How many days come before each month (0-12). */
>> +static const unsigned short __mon_yday[2][13] =
>> +  {
>> +    /* Normal years. */
>> +    {0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365},
>> +    /* Leap years. */
>> +    {0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366}
>> +  };
>> +
>> +#define SECS_PER_HOUR    (60 * 60)
>> +#define SECS_PER_DAY    (SECS_PER_HOUR * 24)
>>     
>
> I wonder if these whould be in a header.  I guess not, if there aren't
> any sites which can use this.
>   

Agree, IMHO, it is not necessary to move it into header.

>   
>> +static void __offtime(__kernel_time_t totalsecs, int offset,
>> +         unsigned int *year, unsigned int *mon, unsigned int *mday,
>> +         unsigned int *hour, unsigned int *min, unsigned int *sec,
>> +         unsigned int *wday, unsigned int *yday)
>> +{
>> +    long days, rem, y;
>> +    const unsigned short *ip;
>> +
>> +    days = totalsecs / SECS_PER_DAY;
>> +    rem = totalsecs % SECS_PER_DAY;
>> +    rem += offset;
>> +    while (rem < 0) {
>> +        rem += SECS_PER_DAY;
>> +        --days;
>> +    }
>> +    while (rem >= SECS_PER_DAY) {
>> +        rem -= SECS_PER_DAY;
>> +        ++days;
>> +    }
>> +
>> +    if (hour)
>> +        *hour = rem / SECS_PER_HOUR;
>> +    rem %= SECS_PER_HOUR;
>> +    if (min)
>> +        *min = rem / 60;
>> +    if (sec)
>> +        *sec = rem % 60;
>> +
>> +    if (wday) {
>> +        /* January 1, 1970 was a Thursday. */
>> +        *wday = (4 + days) % 7;
>> +        if (*wday < 0)
>> +            *wday += 7;
>> +    }
>>     
>
> The code should all be converted to standard kernel style, please. 
> Mainly the use of hard tabs.
>   

Sorry, I'll resend this patch.

>> +    y = 1970;
>> +
>> +#define DIV(a, b) ((a) / (b) - ((a) % (b) < 0))
>>     
>
> hm, I wonder what that does.
>
> It would be clearer to convert this into a regular C function, along
> with a comment whcih explains what it does.
>
>   
>> +#define LEAPS_THRU_END_OF(y) (DIV(y, 4) - DIV(y, 100) + DIV(y, 400))
>>     
>
> Ditto.
>   

It is because I try to keep similar style with code in glibc so that updates
in glibc can easy to applied here.
But actually it looks ugly, I'll fix it.


>   
>> +    while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
>> +        /* Guess a corrected year, assuming 365 days per year. */
>> +        long yg = y + days / 365 - (days % 365 < 0);
>> +
>> +        /* Adjust DAYS and Y to match the guessed year. */
>> +        days -= ((yg - y) * 365
>> +             + LEAPS_THRU_END_OF(yg - 1)
>> +             - LEAPS_THRU_END_OF(y - 1));
>> +        y = yg;
>> +    }
>> +    if (year) {
>> +        *year = y - 1900;
>> +        if (*year != y - 1900) {
>> +            /* The year cannot be represented due to overflow. */
>> +            *year = -1;
>> +        }
>> +    }
>> +
>> +    if (yday)
>> +        *yday = days;
>> +
>> +    ip = __mon_yday[__isleap(y)];
>> +    for (y = 11; days < ip[y]; y--)
>> +        continue;
>> +    days -= ip[y];
>> +    if (mon)
>> +        *mon = y;
>> +    if (mday)
>> +        *mday = days + 1;
>> +}
>>     
>
>   
>> ...
>>
>> +void gmtime(__kernel_time_t totalsecs,
>> +         unsigned int *year, unsigned int *mon, unsigned int *mday,
>> +         unsigned int *hour, unsigned int *min, unsigned int *sec,
>> +         unsigned int *wday, unsigned int *yday)
>> +{
>> +    __offtime(totalsecs, 0, year, mon, mday, hour, min, sec, wday, yday);
>> +}
>> +EXPORT_SYMBOL(gmtime);
>>
>> ...
>>
>> +void localtime(__kernel_time_t totalsecs,
>> +         unsigned int *year, unsigned int *mon, unsigned int *mday,
>> +         unsigned int *hour, unsigned int *min, unsigned int *sec,
>> +         unsigned int *wday, unsigned int *yday)
>> +{
>> +    __offtime(totalsecs, -sys_tz.tz_minuteswest * 60, year, mon, mday, 
>> hour,
>> +        min, sec, wday, yday);
>> +}
>> +EXPORT_SYMBOL(localtime);
>>     
>
> These are such simple wrappers around __offtime() that it might be
> better to make them static inlines in time.h, so callers will end up
> directly calling __offtime() rather than having to remarshal ten
> function arguments.
>   

Good idea, will fix.

Thanks
Zhaolei


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