time: Add y2038 safe read_boot_clock64()

As part of addressing in-kernel y2038 issues, this patch adds
read_boot_clock64() and replaces all the call sites of
read_boot_clock() with this function. This is a __weak
implementation, which simply calls the existing y2038 unsafe
read_boot_clock().

This allows architecture specific implementations to be
converted independently, and eventually the y2038 unsafe
read_boot_clock() can be removed after all its architecture
specific implementations have been converted to
read_boot_clock64().

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1427945681-29972-2-git-send-email-john.stultz@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/timekeeping.h

@@ -269,6 +269,7 @@ static inline bool has_persistent_clock(void)
 
 extern void read_persistent_clock(struct timespec *ts);
 extern void read_boot_clock(struct timespec *ts);
+extern void read_boot_clock64(struct timespec64 *ts);
 extern int update_persistent_clock(struct timespec now);
 
 

kernel/time/timekeeping.c

@@ -1188,6 +1188,14 @@ void __weak read_boot_clock(struct timespec *ts)
 	ts->tv_nsec = 0;
 }
 
+void __weak read_boot_clock64(struct timespec64 *ts64)
+{
+	struct timespec ts;
+
+	read_boot_clock(&ts);
+	*ts64 = timespec_to_timespec64(ts);
+}
+
 /*
  * timekeeping_init - Initializes the clocksource and common timekeeping values
  */
@@ -1209,8 +1217,7 @@ void __init timekeeping_init(void)
 	} else if (now.tv_sec || now.tv_nsec)
 		persistent_clock_exist = true;
 
-	read_boot_clock(&ts);
-	boot = timespec_to_timespec64(ts);
+	read_boot_clock64(&boot);
 	if (!timespec64_valid_strict(&boot)) {
 		pr_warn("WARNING: Boot clock returned invalid value!\n"
 			"         Check your CMOS/BIOS settings.\n");