1 files changed, 87 insertions, 0 deletions
diff --git a/fs/ntfs/time.h b/fs/ntfs/time.h
new file mode 100644
index 000000000..aeed195bd
--- /dev/null
+++ b/fs/ntfs/time.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * NTFS time conversion functions.
+ *
+ * Copyright (c) 2001-2005 Anton Altaparmakov
+ */
+
+#ifndef _LINUX_NTFS_TIME_H
+#define _LINUX_NTFS_TIME_H
+
+#include <linux/time.h>
+#include <asm/div64.h>		/* For do_div(). */
+
+#define NTFS_TIME_OFFSET ((s64)(369 * 365 + 89) * 24 * 3600)
+
+/*
+ * utc2ntfs - convert Linux UTC time to NTFS time
+ * @ts:		Linux UTC time to convert to NTFS time
+ *
+ * Convert the Linux UTC time @ts to its corresponding NTFS time and return
+ * that in little endian format.
+ *
+ * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
+ * and a long tv_nsec where tv_sec is the number of 1-second intervals since
+ * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
+ * intervals since the value of tv_sec.
+ *
+ * NTFS uses Microsoft's standard time format which is stored in a s64 and is
+ * measured as the number of 100-nano-second intervals since 1st January 1601,
+ * 00:00:00 UTC.
+ */
+static inline __le64 utc2ntfs(const struct timespec64 ts)
+{
+	/*
+	 * Convert the seconds to 100ns intervals, add the nano-seconds
+	 * converted to 100ns intervals, and then add the NTFS time offset.
+	 */
+	return cpu_to_le64((u64)(ts.tv_sec + NTFS_TIME_OFFSET) * 10000000 +
+			ts.tv_nsec / 100);
+}
+
+/*
+ * get_current_ntfs_time - get the current time in little endian NTFS format
+ *
+ * Get the current time from the Linux kernel, convert it to its corresponding
+ * NTFS time and return that in little endian format.
+ */
+static inline __le64 get_current_ntfs_time(void)
+{
+	struct timespec64 ts;
+
+	ktime_get_coarse_real_ts64(&ts);
+	return utc2ntfs(ts);
+}
+
+/*
+ * ntfs2utc - convert NTFS time to Linux time
+ * @time:	NTFS time (little endian) to convert to Linux UTC
+ *
+ * Convert the little endian NTFS time @time to its corresponding Linux UTC
+ * time and return that in cpu format.
+ *
+ * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
+ * and a long tv_nsec where tv_sec is the number of 1-second intervals since
+ * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
+ * intervals since the value of tv_sec.
+ *
+ * NTFS uses Microsoft's standard time format which is stored in a s64 and is
+ * measured as the number of 100 nano-second intervals since 1st January 1601,
+ * 00:00:00 UTC.
+ */
+static inline struct timespec64 ntfs2utc(const __le64 time)
+{
+	struct timespec64 ts;
+	s32 t32;
+
+	/* Subtract the NTFS time offset. */
+	s64 t = le64_to_cpu(time) - NTFS_TIME_OFFSET * 10000000;
+	/*
+	 * Convert the time to 1-second intervals and the remainder to
+	 * 1-nano-second intervals.
+	 */
+	ts.tv_sec = div_s64_rem(t, 10000000, &t32);
+	ts.tv_nsec = t32 * 100;
+	return ts;
+}
+#endif /* _LINUX_NTFS_TIME_H */