[PATCH 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 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.

This code is based on code from glibc-2.6

Signed-off-by: Zhao Lei <zhaolei@cn.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);
+
 /**
  * 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.
+ * 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 inline int __isleap(unsigned int year)
+{
+    return (year) % 4 == 0 && ((year) % 100 != 0 || (year) % 400 == 0);
+}
+
+/* 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)
+
+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;
+    }
+
+    y = 1970;
+
+#define DIV(a, b) ((a) / (b) - ((a) % (b) < 0))
+#define LEAPS_THRU_END_OF(y) (DIV(y, 4) - DIV(y, 100) + DIV(y, 400))
+
+    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;
+}
+
+/**
+ * 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).
+ */
+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);
+
+/**
+ * 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.
+ */
+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);
-- 
1.5.5.3