1 files changed, 71 insertions, 0 deletions
diff --git a/fs/isofs/util.c b/fs/isofs/util.c
new file mode 100644
index 000000000..e88dba721
--- /dev/null
+++ b/fs/isofs/util.c
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/isofs/util.c
+ */
+
+#include <linux/time.h>
+#include "isofs.h"
+
+/* 
+ * 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(u8 *p, int flag)
+{
+	int year, month, day, hour, minute, second, tz;
+	int crtime;
+
+	year = p[0];
+	month = p[1];
+	day = p[2];
+	hour = p[3];
+	minute = p[4];
+	second = p[5];
+	if (flag == 0) tz = p[6]; /* High sierra has no time zone */
+	else tz = 0;
+	
+	if (year < 0) {
+		crtime = 0;
+	} else {
+		crtime = mktime64(year+1900, month, day, hour, minute, second);
+
+		/* sign extend */
+		if (tz & 0x80)
+			tz |= (-1 << 8);
+		
+		/* 
+		 * 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 explanation.  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;
+}