1 /* SPDX-License-Identifier: GPL-2.0-or-later */
2 /*
3 * time.h - NTFS time conversion functions. Part of the Linux-NTFS project.
4 *
5 * Copyright (c) 2001-2005 Anton Altaparmakov
6 */
7
8 #ifndef _LINUX_NTFS_TIME_H
9 #define _LINUX_NTFS_TIME_H
10
11 #include <linux/time.h> /* For current_kernel_time(). */
12 #include <asm/div64.h> /* For do_div(). */
13
14 #include "endian.h"
15
16 #define NTFS_TIME_OFFSET ((s64)(369 * 365 + 89) * 24 * 3600 * 10000000)
17
18 /**
19 * utc2ntfs - convert Linux UTC time to NTFS time
20 * @ts: Linux UTC time to convert to NTFS time
21 *
22 * Convert the Linux UTC time @ts to its corresponding NTFS time and return
23 * that in little endian format.
24 *
25 * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
26 * and a long tv_nsec where tv_sec is the number of 1-second intervals since
27 * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
28 * intervals since the value of tv_sec.
29 *
30 * NTFS uses Microsoft's standard time format which is stored in a s64 and is
31 * measured as the number of 100-nano-second intervals since 1st January 1601,
32 * 00:00:00 UTC.
33 */
34 static inline sle64 utc2ntfs(const struct timespec64 ts)
35 {
36 /*
37 * Convert the seconds to 100ns intervals, add the nano-seconds
38 * converted to 100ns intervals, and then add the NTFS time offset.
39 */
40 return cpu_to_sle64((s64)ts.tv_sec * 10000000 + ts.tv_nsec / 100 +
41 NTFS_TIME_OFFSET);
42 }
43
44 /**
45 * get_current_ntfs_time - get the current time in little endian NTFS format
46 *
47 * Get the current time from the Linux kernel, convert it to its corresponding
48 * NTFS time and return that in little endian format.
49 */
50 static inline sle64 get_current_ntfs_time(void)
51 {
52 struct timespec64 ts;
53
54 ktime_get_coarse_real_ts64(&ts);
55 return utc2ntfs(ts);
56 }
57
58 /**
59 * ntfs2utc - convert NTFS time to Linux time
60 * @time: NTFS time (little endian) to convert to Linux UTC
61 *
62 * Convert the little endian NTFS time @time to its corresponding Linux UTC
63 * time and return that in cpu format.
64 *
65 * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
66 * and a long tv_nsec where tv_sec is the number of 1-second intervals since
67 * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
68 * intervals since the value of tv_sec.
69 *
70 * NTFS uses Microsoft's standard time format which is stored in a s64 and is
71 * measured as the number of 100 nano-second intervals since 1st January 1601,
72 * 00:00:00 UTC.
73 */
74 static inline struct timespec64 ntfs2utc(const sle64 time)
75 {
76 struct timespec64 ts;
77
78 /* Subtract the NTFS time offset. */
79 u64 t = (u64)(sle64_to_cpu(time) - NTFS_TIME_OFFSET);
80 /*
81 * Convert the time to 1-second intervals and the remainder to
82 * 1-nano-second intervals.
83 */
84 ts.tv_nsec = do_div(t, 10000000) * 100;
85 ts.tv_sec = t;
86 return ts;
87 }
88
89 #endif /* _LINUX_NTFS_TIME_H */