alarmtimer: Add functions for timerfd support

Add functions needed for hooking up alarmtimer to timerfd:

* alarm_restart: Similar to hrtimer_restart, restart an alarmtimer after
  the expires time has already been updated (as with alarm_forward).

* alarm_forward_now: Similar to hrtimer_forward_now, move the expires
  time forward to an interval from the current time of the associated clock.

* alarm_start_relative: Start an alarmtimer with an expires time relative to
  the current time of the associated clock.

* alarm_expires_remaining: Similar to hrtimer_expires_remaining, return the
  amount of time remaining until alarm expiry.
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>

include/linux/alarmtimer.h

@@ -44,10 +44,14 @@ struct alarm {
 void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
 		enum alarmtimer_restart (*function)(struct alarm *, ktime_t));
 int alarm_start(struct alarm *alarm, ktime_t start);
+int alarm_start_relative(struct alarm *alarm, ktime_t start);
+void alarm_restart(struct alarm *alarm);
 int alarm_try_to_cancel(struct alarm *alarm);
 int alarm_cancel(struct alarm *alarm);
 
 u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval);
+u64 alarm_forward_now(struct alarm *alarm, ktime_t interval);
+ktime_t alarm_expires_remaining(const struct alarm *alarm);
 
 /* Provide way to access the rtc device being used by alarmtimers */
 struct rtc_device *alarmtimer_get_rtcdev(void);

kernel/time/alarmtimer.c

@@ -199,6 +199,12 @@ static enum hrtimer_restart alarmtimer_fired(struct hrtimer *timer)
 
 }
 
+ktime_t alarm_expires_remaining(const struct alarm *alarm)
+{
+	struct alarm_base *base = &alarm_bases[alarm->type];
+	return ktime_sub(alarm->node.expires, base->gettime());
+}
+
 #ifdef CONFIG_RTC_CLASS
 /**
  * alarmtimer_suspend - Suspend time callback
@@ -305,7 +311,7 @@ void alarm_init(struct alarm *alarm, enum alarmtimer_type type,
 }
 
 /**
- * alarm_start - Sets an alarm to fire
+ * alarm_start - Sets an absolute alarm to fire
  * @alarm: ptr to alarm to set
  * @start: time to run the alarm
  */
@@ -324,6 +330,31 @@ int alarm_start(struct alarm *alarm, ktime_t start)
 	return ret;
 }
 
+/**
+ * alarm_start_relative - Sets a relative alarm to fire
+ * @alarm: ptr to alarm to set
+ * @start: time relative to now to run the alarm
+ */
+int alarm_start_relative(struct alarm *alarm, ktime_t start)
+{
+	struct alarm_base *base = &alarm_bases[alarm->type];
+
+	start = ktime_add(start, base->gettime());
+	return alarm_start(alarm, start);
+}
+
+void alarm_restart(struct alarm *alarm)
+{
+	struct alarm_base *base = &alarm_bases[alarm->type];
+	unsigned long flags;
+
+	spin_lock_irqsave(&base->lock, flags);
+	hrtimer_set_expires(&alarm->timer, alarm->node.expires);
+	hrtimer_restart(&alarm->timer);
+	alarmtimer_enqueue(base, alarm);
+	spin_unlock_irqrestore(&base->lock, flags);
+}
+
 /**
  * alarm_try_to_cancel - Tries to cancel an alarm timer
  * @alarm: ptr to alarm to be canceled
@@ -394,6 +425,12 @@ u64 alarm_forward(struct alarm *alarm, ktime_t now, ktime_t interval)
 	return overrun;
 }
 
+u64 alarm_forward_now(struct alarm *alarm, ktime_t interval)
+{
+	struct alarm_base *base = &alarm_bases[alarm->type];
+
+	return alarm_forward(alarm, base->gettime(), interval);
+}