patch-2.1.32 linux/fs/isofs/util.c

• Lines: 58
• Date: Thu Apr 3 10:23:56 1997
• Orig file: v2.1.31/linux/fs/isofs/util.c
• Orig date: Tue May 28 21:26:48 1996

diff -u --recursive --new-file v2.1.31/linux/fs/isofs/util.c linux/fs/isofs/util.c
@@ -84,10 +84,16 @@
 	return (isonum_731 (p));
 }
 
-/* We have to convert from a MM/DD/YY format to the unix ctime format.  We have to
-   take into account leap years and all of that good stuff.  Unfortunately, the kernel
-   does not have the information on hand to take into account daylight savings time,
-   so there will be cases (roughly half the time) where the dates are off by one hour. */
+/* 
+ * We have to convert from a MM/DD/YY format to the unix ctime format.
+ * We have to take into account leap years and all of that good stuff.
+ * Unfortunately, the kernel does not have the information on hand to
+ * take into account daylight savings time, but it shouldn't matter.
+ * The time stored should be localtime (with or without DST in effect),
+ * and the timezone offset should hold the offset required to get back
+ * to GMT.  Thus  we should always be correct.
+ */
+
 int iso_date(char * p, int flag)
 {
 	int year, month, day, hour ,minute, second, tz;
@@ -121,9 +127,33 @@
 		if (tz & 0x80)
 			tz |= (-1 << 8);
 		
-		/* timezone offset is unreliable on some disks */
-		if (-48 <= tz && tz <= 52)
-			crtime += tz * 15 * 60;
+		/* 
+		 * The timezone offset is unreliable on some disks,
+		 * so we make a sanity check.  In no case is it ever
+		 * more than 13 hours from GMT, which is 52*15min.
+		 * The time is always stored in localtime with the
+		 * timezone offset being what get added to GMT to
+		 * get to localtime.  Thus we need to subtract the offset
+		 * to get to true GMT, which is what we store the time
+		 * as internally.  On the local system, the user may set
+		 * their timezone any way they wish, of course, so GMT
+		 * gets converted back to localtime on the receiving
+		 * system.
+		 *
+		 * NOTE: mkisofs in versions prior to mkisofs-1.10 had
+		 * the sign wrong on the timezone offset.  This has now
+		 * been corrected there too, but if you are getting screwy
+		 * results this may be the explaination.  If enough people
+		 * complain, a user configuration option could be added
+		 * to add the timezone offset in with the wrong sign
+		 * for 'compatibility' with older discs, but I cannot see how
+		 * it will matter that much.
+		 *
+		 * Thanks to kuhlmav@elec.canterbury.ac.nz (Volker Kuhlmann)
+		 * for pointing out the sign error.
+		 */
+		if (-52 <= tz && tz <= 52)
+			crtime -= tz * 15 * 60;
 	}
 	return crtime;
 }