[PATCH v2 1/2] Add function to convert between calendar time and broken-down time for universal use

[Zhaolei <zhaolei@cn.fujitsu.com>]

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 convert,
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.

This code is based on code from glibc-2.6

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
---
 include/linux/time.h   |   62 +++++++++++++++++++
 kernel/time/Makefile   |    2 +-
 kernel/time/timeconv.c |  153 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 216 insertions(+), 1 deletions(-)
 create mode 100644 kernel/time/timeconv.c

diff --git a/include/linux/time.h b/include/linux/time.h
index ea16c1a..658f8e1 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -151,6 +151,68 @@ extern void update_xtime_cache(u64 nsec);
 struct tms;
 extern void do_sys_times(struct tms *);
 
+extern 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);
+
+/**
+ * gmtime - converts the calendar time to UTC broken-down time
+ *
+ * @totalsecs	The number of seconds elapsed since 00:00:00 on January 1, 1970,
+ *		Coordinated Universal Time (UTC).
+ * @year	Store the number of years since 1900.
+ * @mon		Store the number of months since January, in the range 0 to 11.
+ * @mday	Store the day of the month, in the range 1 to 31.
+ * @hour	Store the number of hours past midnight, in the range 0 to 23.
+ * @min		Store the number of minutes after the hour,
+ *		in the range 0 to 59.
+ * @sec		Store the number of seconds after the minute, normally in the
+ *		range 0 to 59, but can be up to 60 to allow for leap seconds.
+ * @wday	Store the number of days since Sunday, in the range 0 to 6.
+ * @yday	Store the number of days since January 1, in the range 0 to 365.
+ *
+ * Similar to the gmtime() in glibc, broken-down time is expressed in
+ * Coordinated Universal Time (UTC).
+ */
+static inline 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);
+}
+
+/**
+ * localtime - converts the calendar time to local broken-down time
+ *
+ * @totalsecs	The number of seconds elapsed since 00:00:00 on January 1, 1970,
+ *		Coordinated Universal Time (UTC).
+ * @year	Store the number of years since 1900.
+ * @mon		Store the number of months since January, in the range 0 to 11.
+ * @mday	Store the day of the month, in the range 1 to 31.
+ * @hour	Store the number of hours past midnight, in the range 0 to 23.
+ * @min		Store the number of minutes after the hour,
+ *		in the range 0 to 59.
+ * @sec		Store the number of seconds after the minute, normally in the
+ *		range 0 to 59, but can be up to 60 to allow for leap seconds.
+ * @wday	Store the number of days since Sunday, in the range 0 to 6.
+ * @yday	Store the number of days since January 1, in the range 0 to 365.
+ *
+ * Similar to the localtime() in glibc, broken-down time is expressed
+ * relative to sys_tz.
+ */
+static inline 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);
+}
+
 /**
  * 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..b28fcec
--- /dev/null
+++ b/kernel/time/timeconv.c
@@ -0,0 +1,153 @@
+/*
+ * Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
+ * This file is part of the GNU C Library.
+ * Contributed by Paul Eggert (eggert@twinsun.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@cn.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 int __isleap(unsigned int year)
+{
+	return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
+}
+
+/* do a mathdiv for long type */
+static long math_div(long a, long b)
+{
+	return a / b - (a % b < 0);
+}
+
+/* How many leap years between y1 and y2, y1 must less or equal to y2 */
+static long leaps_between(long y1, long y2)
+{
+	long leaps1 = math_div(y1 - 1, 4) - math_div(y1 - 1, 100)
+		+ math_div(y1 - 1, 400);
+	long leaps2 = math_div(y2 - 1, 4) - math_div(y2 - 1, 100)
+		+ math_div(y2 - 1, 400);
+	return leaps2 - leaps1;
+}
+
+/* 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)
+
+/**
+ * __offtime - converts the calendar time to local broken-down time
+ *
+ * @totalsecs	The number of seconds elapsed since 00:00:00 on January 1, 1970,
+ *		Coordinated Universal Time (UTC).
+ * @offset	Offset seconds adding to totalsecs.
+ * @year	Store the number of years since 1900.
+ * @mon		Store the number of months since January, in the range 0 to 11.
+ * @mday	Store the day of the month, in the range 1 to 31.
+ * @hour	Store the number of hours past midnight, in the range 0 to 23.
+ * @min		Store the number of minutes after the hour,
+ *		in the range 0 to 59.
+ * @sec		Store the number of seconds after the minute, normally in the
+ *		range 0 to 59, but can be up to 60 to allow for leap seconds.
+ * @wday	Store the number of days since Sunday, in the range 0 to 6.
+ * @yday	Store the number of days since January 1, in the range 0 to 365.
+ *
+ * This function is for internal use, call gmtime() and localtime() instead.
+ */
+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;
+	}
+
+	y = 1970;
+
+	while (days < 0 || days >= (__isleap(y) ? 366 : 365)) {
+		/* Guess a corrected year, assuming 365 days per year. */
+		long yg = y + math_div(days, 365);
+
+		/* Adjust DAYS and Y to match the guessed year. */
+		days -= (yg - y) * 365 + leaps_between(y, yg);
+		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;
+}
+EXPORT_SYMBOL(__offtime);
-- 
1.5.5.3