fs/isofs/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
  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 }