1 files changed, 15 insertions, 42 deletions

diff --git a/fs/fat/misc.c b/fs/fat/misc.c
index 0f55f5cb732f..d3da05f26465 100644
--- a/fs/fat/misc.c
+++ b/fs/fat/misc.c
@@ -9,6 +9,7 @@
 #include <linux/module.h>
 #include <linux/fs.h>
 #include <linux/buffer_head.h>
+#include <linux/time.h>
 #include "fat.h"
 
 /*
@@ -157,10 +158,6 @@ extern struct timezone sys_tz;
 #define SECS_PER_MIN    60
 #define SECS_PER_HOUR   (60 * 60)
 #define SECS_PER_DAY    (SECS_PER_HOUR * 24)
-#define UNIX_SECS_1980  315532800L
-#if BITS_PER_LONG == 64
-#define UNIX_SECS_2108  4354819200L
-#endif
 /* days between 1.1.70 and 1.1.80 (2 leap days) */
 #define DAYS_DELTA      (365 * 10 + 2)
 /* 120 (2100 - 1980) isn't leap year */
@@ -213,58 +210,35 @@ void fat_time_fat2unix(struct msdos_sb_info *sbi, struct timespec *ts,
 void fat_time_unix2fat(struct msdos_sb_info *sbi, struct timespec *ts,
                        __le16 *time, __le16 *date, u8 *time_cs)
 {
-        time_t second = ts->tv_sec;
-        time_t day, leap_day, month, year;
+        struct tm tm;
+        time_to_tm(ts->tv_sec, sbi->options.tz_utc ? 0 :
+                   -sys_tz.tz_minuteswest * 60, &tm);
 
-        if (!sbi->options.tz_utc)
-                second -= sys_tz.tz_minuteswest * SECS_PER_MIN;
-
-        /* Jan 1 GMT 00:00:00 1980. But what about another time zone? */
-        if (second < UNIX_SECS_1980) {
+        /*  FAT can only support year between 1980 to 2107 */
+        if (tm.tm_year < 1980 - 1900) {
                 *time = 0;
                 *date = cpu_to_le16((0 << 9) | (1 << 5) | 1);
                 if (time_cs)
                         *time_cs = 0;
                 return;
         }
-#if BITS_PER_LONG == 64
-        if (second >= UNIX_SECS_2108) {
+        if (tm.tm_year > 2107 - 1900) {
                 *time = cpu_to_le16((23 << 11) | (59 << 5) | 29);
                 *date = cpu_to_le16((127 << 9) | (12 << 5) | 31);
                 if (time_cs)
                         *time_cs = 199;
                 return;
         }
-#endif
 
-        day = second / SECS_PER_DAY - DAYS_DELTA;
-        year = day / 365;
-        leap_day = (year + 3) / 4;
-        if (year > YEAR_2100)           /* 2100 isn't leap year */
-                leap_day--;
-        if (year * 365 + leap_day > day)
-                year--;
-        leap_day = (year + 3) / 4;
-        if (year > YEAR_2100)           /* 2100 isn't leap year */
-                leap_day--;
-        day -= year * 365 + leap_day;
-
-        if (IS_LEAP_YEAR(year) && day == days_in_year[3]) {
-                month = 2;
-        } else {
-                if (IS_LEAP_YEAR(year) && day > days_in_year[3])
-                        day--;
-                for (month = 1; month < 12; month++) {
-                        if (days_in_year[month + 1] > day)
-                                break;
-                }
-        }
-        day -= days_in_year[month];
+        /* from 1900 -> from 1980 */
+        tm.tm_year -= 80;
+        /* 0~11 -> 1~12 */
+        tm.tm_mon++;
+        /* 0~59 -> 0~29(2sec counts) */
+        tm.tm_sec >>= 1;
 
-        *time = cpu_to_le16(((second / SECS_PER_HOUR) % 24) << 11
-                            | ((second / SECS_PER_MIN) % 60) << 5
-                            | (second % SECS_PER_MIN) >> 1);
-        *date = cpu_to_le16((year << 9) | (month << 5) | (day + 1));
+        *time = cpu_to_le16(tm.tm_hour << 11 | tm.tm_min << 5 | tm.tm_sec);
+        *date = cpu_to_le16(tm.tm_year << 9 | tm.tm_mon << 5 | tm.tm_mday);
         if (time_cs)
                 *time_cs = (ts->tv_sec & 1) * 100 + ts->tv_nsec / 10000000;
 }
@@ -285,4 +259,3 @@ int fat_sync_bhs(struct buffer_head **bhs, int nr_bhs)
         }
         return err;
 }
-