1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/fs/isofs/util.c
4 */
5
6#include <linux/time.h>
7#include "isofs.h"
8
9/*
10 * We have to convert from a MM/DD/YY format to the Unix ctime format.
11 * We have to take into account leap years and all of that good stuff.
12 * Unfortunately, the kernel does not have the information on hand to
13 * take into account daylight savings time, but it shouldn't matter.
14 * The time stored should be localtime (with or without DST in effect),
15 * and the timezone offset should hold the offset required to get back
16 * to GMT. Thus we should always be correct.
17 */
18
19struct timespec64 iso_date(u8 *p, int flags)
20{
21 int year, month, day, hour, minute, second, tz;
22 struct timespec64 ts;
23
24 if (flags & ISO_DATE_LONG_FORM) {
25 year = (p[0] - '0') * 1000 +
26 (p[1] - '0') * 100 +
27 (p[2] - '0') * 10 +
28 (p[3] - '0') - 1900;
29 month = ((p[4] - '0') * 10 + (p[5] - '0'));
30 day = ((p[6] - '0') * 10 + (p[7] - '0'));
31 hour = ((p[8] - '0') * 10 + (p[9] - '0'));
32 minute = ((p[10] - '0') * 10 + (p[11] - '0'));
33 second = ((p[12] - '0') * 10 + (p[13] - '0'));
34 ts.tv_nsec = ((p[14] - '0') * 10 + (p[15] - '0')) * 10000000;
35 tz = p[16];
36 } else {
37 year = p[0];
38 month = p[1];
39 day = p[2];
40 hour = p[3];
41 minute = p[4];
42 second = p[5];
43 ts.tv_nsec = 0;
44 /* High sierra has no time zone */
45 tz = flags & ISO_DATE_HIGH_SIERRA ? 0 : p[6];
46 }
47
48 if (year < 0) {
49 ts.tv_sec = 0;
50 } else {
51 ts.tv_sec = mktime64(year: year+1900, mon: month, day, hour, min: minute, sec: second);
52
53 /* sign extend */
54 if (tz & 0x80)
55 tz |= (-1 << 8);
56
57 /*
58 * The timezone offset is unreliable on some disks,
59 * so we make a sanity check. In no case is it ever
60 * more than 13 hours from GMT, which is 52*15min.
61 * The time is always stored in localtime with the
62 * timezone offset being what get added to GMT to
63 * get to localtime. Thus we need to subtract the offset
64 * to get to true GMT, which is what we store the time
65 * as internally. On the local system, the user may set
66 * their timezone any way they wish, of course, so GMT
67 * gets converted back to localtime on the receiving
68 * system.
69 *
70 * NOTE: mkisofs in versions prior to mkisofs-1.10 had
71 * the sign wrong on the timezone offset. This has now
72 * been corrected there too, but if you are getting screwy
73 * results this may be the explanation. If enough people
74 * complain, a user configuration option could be added
75 * to add the timezone offset in with the wrong sign
76 * for 'compatibility' with older discs, but I cannot see how
77 * it will matter that much.
78 *
79 * Thanks to kuhlmav@elec.canterbury.ac.nz (Volker Kuhlmann)
80 * for pointing out the sign error.
81 */
82 if (-52 <= tz && tz <= 52)
83 ts.tv_sec -= tz * 15 * 60;
84 }
85 return ts;
86}
87