time: Introduce timekeeping_inject_offset

This adds a kernel-internal timekeeping interface to add or subtract
a fixed amount from CLOCK_REALTIME. This makes it so kernel users or
interfaces trying to do so do not have to read the time, then add an
offset and then call settimeofday(), which adds some extra error in
comparision to just simply adding the offset in the kernel timekeeping
core.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Richard Cochran <richard.cochran@omicron.at>
LKML-Reference: <20110201134419.584311693@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/time.h b/include/linux/time.h
index 7c44e777803377f597e15c63b825380fc343356b..379b9037b5b44f8bd8c656a608c3c88c52dfaa9c 100644 (file)
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -166,6 +166,7 @@ extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
 extern int timekeeping_valid_for_hres(void);
 extern u64 timekeeping_max_deferment(void);
 extern void timekeeping_leap_insert(int leapsecond);
+extern int timekeeping_inject_offset(struct timespec *ts);
 
 struct tms;
 extern void do_sys_times(struct tms *);

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4f9f65b9132386185d63caa4d87a74c8cda2fba9..6262c1d183972ead4c1813502cff4168d29cea97 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -387,6 +387,42 @@ int do_settimeofday(const struct timespec *tv)
 
 EXPORT_SYMBOL(do_settimeofday);
 
+
+/**
+ * timekeeping_inject_offset - Adds or subtracts from the current time.
+ * @tv:                pointer to the timespec variable containing the offset
+ *
+ * Adds or subtracts an offset value from the current time.
+ */
+int timekeeping_inject_offset(struct timespec *ts)
+{
+       unsigned long flags;
+
+       if ((unsigned long)ts->tv_nsec >= NSEC_PER_SEC)
+               return -EINVAL;
+
+       write_seqlock_irqsave(&xtime_lock, flags);
+
+       timekeeping_forward_now();
+
+       xtime = timespec_add(xtime, *ts);
+       wall_to_monotonic = timespec_sub(wall_to_monotonic, *ts);
+
+       timekeeper.ntp_error = 0;
+       ntp_clear();
+
+       update_vsyscall(&xtime, &wall_to_monotonic, timekeeper.clock,
+                               timekeeper.mult);
+
+       write_sequnlock_irqrestore(&xtime_lock, flags);
+
+       /* signal hrtimers about time change */
+       clock_was_set();
+
+       return 0;
+}
+EXPORT_SYMBOL(timekeeping_inject_offset);
+
 /**
  * change_clocksource - Swaps clocksources if a new one is available
  *