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Message-Id: <ab3102e23721f82df9841af9584c6c4b12501869.1335510125.git.richardcochran@gmail.com>
Date: Fri, 27 Apr 2012 10:12:40 +0200
From: Richard Cochran <richardcochran@...il.com>
To: <linux-kernel@...r.kernel.org>
Cc: John Stultz <john.stultz@...aro.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH RFC V1 1/5] Add functions to convert continuous timescales to UTC.
This patch adds a pair of inline helper functions to convert from
one timescale to the other, around a given leap second threshold.
Also, it adds an academic compile time option to support deleting
leap seconds.
Signed-off-by: Richard Cochran <richardcochran@...il.com>
---
kernel/time/Kconfig | 12 ++++++
kernel/time/utc-tai.h | 99 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 111 insertions(+), 0 deletions(-)
create mode 100644 kernel/time/utc-tai.h
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index a20dc8a..1569aef 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -26,6 +26,18 @@ config HIGH_RES_TIMERS
hardware is not capable then this option only increases
the size of the kernel image.
+config DELETE_LEAP_SECONDS
+ bool "Support deletion of leap seconds"
+ default y
+ help
+ This option enables support for leap second deletion via the
+ STA_DEL control bit in the NTP adjtimex system call.
+
+ Historically, leap seconds have only ever been inserted,
+ never deleted. Saying no here results in a slightly smaller
+ kernel image. If you believe that Earth's rotational speed
+ might one day increase, then say yes here.
+
config GENERIC_CLOCKEVENTS_BUILD
bool
default y
diff --git a/kernel/time/utc-tai.h b/kernel/time/utc-tai.h
new file mode 100644
index 0000000..ffc3ae9
--- /dev/null
+++ b/kernel/time/utc-tai.h
@@ -0,0 +1,99 @@
+/*
+ * linux/kernel/time/utc-tai.h
+ *
+ * Converts between TAI and UTC by applying the offset correction.
+ *
+ * Copyright (C) 2012 Richard Cochran <richardcochran@...il.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+#ifndef __LINUX_KERNEL_TIME_UTC_TAI_H
+#define __LINUX_KERNEL_TIME_UTC_TAI_H
+
+#include <linux/types.h>
+
+static inline time_t __tai_to_utc(time_t tai, time_t next, int offset)
+{
+ time_t utc = tai - offset;
+
+ if (unlikely(tai >= next))
+ utc--;
+
+ return utc;
+}
+
+static inline time_t __utc_to_tai(time_t utc, time_t next, int offset)
+{
+ time_t leapsec = next - offset;
+ time_t result = utc + offset;
+
+ if (unlikely(utc >= leapsec))
+ result++;
+
+ return result;
+}
+
+#ifdef CONFIG_DELETE_LEAP_SECONDS
+
+static inline time_t tai_to_utc(time_t tai, time_t next, int offset, int insert)
+{
+ if (likely(insert))
+ return __tai_to_utc(tai, next, offset);
+
+ if (unlikely(tai > next))
+ return tai - offset + 1;
+
+ return tai - offset;
+}
+
+static inline time_t utc_to_tai(time_t utc, time_t next, int offset, int insert)
+{
+ time_t leapsec, result;
+
+ if (likely(insert))
+ return __utc_to_tai(utc, next, offset);
+
+ leapsec = next - offset + 1;
+
+ if (unlikely(utc > leapsec))
+ result = utc + offset - 1;
+ else if (utc < leapsec)
+ result = utc + offset;
+ else {
+ /*
+ * Ouch, this time never existed.
+ */
+ result = next;
+ }
+
+ return result;
+}
+
+#else /*CONFIG_DELETE_LEAP_SECONDS*/
+
+static inline time_t tai_to_utc(time_t tai, time_t next, int offset, int insert)
+{
+ return __tai_to_utc(tai, next, offset);
+}
+
+static inline time_t utc_to_tai(time_t utc, time_t next, int offset, int insert)
+{
+ return __utc_to_tai(utc, next, offset);
+}
+
+#endif /*!CONFIG_DELETE_LEAP_SECONDS*/
+
+#endif
--
1.7.2.5
--
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