1 /*
2  * time.h - NTFS time conversion functions.  Part of the Linux-NTFS project.
3  *
4  * Copyright (c) 2001-2005 Anton Altaparmakov
5  *
6  * This program/include file is free software; you can redistribute it and/or
7  * modify it under the terms of the GNU General Public License as published
8  * by the Free Software Foundation; either version 2 of the License, or
9  * (at your option) any later version.
10  *
11  * This program/include file is distributed in the hope that it will be
12  * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
13  * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  * GNU General Public License for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * along with this program (in the main directory of the Linux-NTFS
18  * distribution in the file COPYING); if not, write to the Free Software
19  * Foundation,Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
20  */
21 
22 #ifndef _LINUX_NTFS_TIME_H
23 #define _LINUX_NTFS_TIME_H
24 
25 #include <linux/time.h>		/* For current_kernel_time(). */
26 #include <asm/div64.h>		/* For do_div(). */
27 
28 #include "endian.h"
29 
30 #define NTFS_TIME_OFFSET ((s64)(369 * 365 + 89) * 24 * 3600 * 10000000)
31 
32 /**
33  * utc2ntfs - convert Linux UTC time to NTFS time
34  * @ts:		Linux UTC time to convert to NTFS time
35  *
36  * Convert the Linux UTC time @ts to its corresponding NTFS time and return
37  * that in little endian format.
38  *
39  * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
40  * and a long tv_nsec where tv_sec is the number of 1-second intervals since
41  * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
42  * intervals since the value of tv_sec.
43  *
44  * NTFS uses Microsoft's standard time format which is stored in a s64 and is
45  * measured as the number of 100-nano-second intervals since 1st January 1601,
46  * 00:00:00 UTC.
47  */
utc2ntfs(const struct timespec64 ts)48 static inline sle64 utc2ntfs(const struct timespec64 ts)
49 {
50 	/*
51 	 * Convert the seconds to 100ns intervals, add the nano-seconds
52 	 * converted to 100ns intervals, and then add the NTFS time offset.
53 	 */
54 	return cpu_to_sle64((s64)ts.tv_sec * 10000000 + ts.tv_nsec / 100 +
55 			NTFS_TIME_OFFSET);
56 }
57 
58 /**
59  * get_current_ntfs_time - get the current time in little endian NTFS format
60  *
61  * Get the current time from the Linux kernel, convert it to its corresponding
62  * NTFS time and return that in little endian format.
63  */
get_current_ntfs_time(void)64 static inline sle64 get_current_ntfs_time(void)
65 {
66 	struct timespec64 ts;
67 
68 	ktime_get_coarse_real_ts64(&ts);
69 	return utc2ntfs(ts);
70 }
71 
72 /**
73  * ntfs2utc - convert NTFS time to Linux time
74  * @time:	NTFS time (little endian) to convert to Linux UTC
75  *
76  * Convert the little endian NTFS time @time to its corresponding Linux UTC
77  * time and return that in cpu format.
78  *
79  * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
80  * and a long tv_nsec where tv_sec is the number of 1-second intervals since
81  * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
82  * intervals since the value of tv_sec.
83  *
84  * NTFS uses Microsoft's standard time format which is stored in a s64 and is
85  * measured as the number of 100 nano-second intervals since 1st January 1601,
86  * 00:00:00 UTC.
87  */
ntfs2utc(const sle64 time)88 static inline struct timespec64 ntfs2utc(const sle64 time)
89 {
90 	struct timespec64 ts;
91 
92 	/* Subtract the NTFS time offset. */
93 	u64 t = (u64)(sle64_to_cpu(time) - NTFS_TIME_OFFSET);
94 	/*
95 	 * Convert the time to 1-second intervals and the remainder to
96 	 * 1-nano-second intervals.
97 	 */
98 	ts.tv_nsec = do_div(t, 10000000) * 100;
99 	ts.tv_sec = t;
100 	return ts;
101 }
102 
103 #endif /* _LINUX_NTFS_TIME_H */
104