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
19 int iso_date(u8 *p, int flag)
20 {
21 int year, month, day, hour, minute, second, tz;
22 int crtime;
23
24 year = p[0];
25 month = p[1];
26 day = p[2];
27 hour = p[3];
28 minute = p[4];
29 second = p[5];
30 if (flag == 0) tz = p[6]; /* High sierra has no time zone */
31 else tz = 0;
32
33 if (year < 0) {
34 crtime = 0;
35 } else {
36 crtime = mktime64(year+1900, month, day, hour, minute, second);
37
38 /* sign extend */
39 if (tz & 0x80)
40 tz |= (-1 << 8);
41
42 /*
43 * The timezone offset is unreliable on some disks,
44 * so we make a sanity check. In no case is it ever
45 * more than 13 hours from GMT, which is 52*15min.
46 * The time is always stored in localtime with the
47 * timezone offset being what get added to GMT to
48 * get to localtime. Thus we need to subtract the offset
49 * to get to true GMT, which is what we store the time
50 * as internally. On the local system, the user may set
51 * their timezone any way they wish, of course, so GMT
52 * gets converted back to localtime on the receiving
53 * system.
54 *
55 * NOTE: mkisofs in versions prior to mkisofs-1.10 had
56 * the sign wrong on the timezone offset. This has now
57 * been corrected there too, but if you are getting screwy
58 * results this may be the explanation. If enough people
59 * complain, a user configuration option could be added
60 * to add the timezone offset in with the wrong sign
61 * for 'compatibility' with older discs, but I cannot see how
62 * it will matter that much.
63 *
64 * Thanks to kuhlmav@elec.canterbury.ac.nz (Volker Kuhlmann)
65 * for pointing out the sign error.
66 */
67 if (-52 <= tz && tz <= 52)
68 crtime -= tz * 15 * 60;
69 }
70 return crtime;
71 }