util.c

 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+1900, month, day, hour, minute, 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}