2 files changed, 37 insertions, 0 deletions

diff --git a/include/linux/time.h b/include/linux/time.h
index 7c44e7778033..379b9037b5b4 100644
--- 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 4f9f65b91323..6262c1d18397 100644
--- 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
  *