[PATCH 0/2] timerfd support for wakeup alarm timers

[PATCH 0/2] timerfd support for wakeup alarm timers

[Todd Poynor]

Enable wakeup alarm timers via file descriptors.  Hook up alarmtimer
to timerfd via clocks CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM,
and add needed functions to alarmtimer.

 fs/timerfd.c               |  131 +++++++++++++++++++++++++++++++++++++--------
 include/linux/alarmtimer.h |    4 +
 kernel/time/alarmtimer.c   |   39 +++++++++++++
 3 files changed, 150 insertions(+), 24 deletions(-)

[PATCH 1/2] alarmtimer: add functions for timerfd support

[Todd Poynor]

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>
---
 include/linux/alarmtimer.h |  4 ++++
 kernel/time/alarmtimer.c   | 39 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/include/linux/alarmtimer.h b/include/linux/alarmtimer.h
index 9069694..a899402 100644
--- a/include/linux/alarmtimer.h
+++ b/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);
diff --git a/kernel/time/alarmtimer.c b/kernel/time/alarmtimer.c
index f11d83b..3e5cba2 100644
--- a/kernel/time/alarmtimer.c
+++ b/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
  */
@@ -325,6 +331,31 @@ int alarm_start(struct alarm *alarm, ktime_t start)
 }
 
 /**
+ * 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);
+}
 
 
 
-- 
1.8.2.1

[PATCH 2/2] timerfd: add alarm timers

[Todd Poynor]

Add support for clocks CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM,
thereby enabling wakeup alarm timers via file descriptors.

Signed-off-by: Todd Poynor <toddpoynor@google.com>
---
 fs/timerfd.c | 131 ++++++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 108 insertions(+), 23 deletions(-)

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 32b644f..9293121 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -8,6 +8,7 @@
  *
  */
 
+#include <linux/alarmtimer.h>
 #include <linux/file.h>
 #include <linux/poll.h>
 #include <linux/init.h>
@@ -26,7 +27,10 @@
 #include <linux/rcupdate.h>
 
 struct timerfd_ctx {
-	struct hrtimer tmr;
+	union {
+		struct hrtimer tmr;
+		struct alarm alarm;
+	} t;
 	ktime_t tintv;
 	ktime_t moffs;
 	wait_queue_head_t wqh;
@@ -41,14 +45,19 @@ struct timerfd_ctx {
 static LIST_HEAD(cancel_list);
 static DEFINE_SPINLOCK(cancel_lock);
 
+static inline bool isalarm(struct timerfd_ctx *ctx)
+{
+	return ctx->clockid == CLOCK_REALTIME_ALARM ||
+		ctx->clockid == CLOCK_BOOTTIME_ALARM;
+}
+
 /*
  * This gets called when the timer event triggers. We set the "expired"
  * flag, but we do not re-arm the timer (in case it's necessary,
  * tintv.tv64 != 0) until the timer is accessed.
  */
-static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
+static void timerfd_triggered(struct timerfd_ctx *ctx)
 {
-	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx, tmr);
 	unsigned long flags;
 
 	spin_lock_irqsave(&ctx->wqh.lock, flags);
@@ -56,10 +65,25 @@ static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
 	ctx->ticks++;
 	wake_up_locked(&ctx->wqh);
 	spin_unlock_irqrestore(&ctx->wqh.lock, flags);
+}
 
+static enum hrtimer_restart timerfd_tmrproc(struct hrtimer *htmr)
+{
+	struct timerfd_ctx *ctx = container_of(htmr, struct timerfd_ctx,
+					       t.tmr);
+	timerfd_triggered(ctx);
 	return HRTIMER_NORESTART;
 }
 
+static enum alarmtimer_restart timerfd_alarmproc(struct alarm *alarm,
+	ktime_t now)
+{
+	struct timerfd_ctx *ctx = container_of(alarm, struct timerfd_ctx,
+					       t.alarm);
+	timerfd_triggered(ctx);
+	return ALARMTIMER_NORESTART;
+}
+
 /*
  * Called when the clock was set to cancel the timers in the cancel
  * list. This will wake up processes waiting on these timers. The
@@ -107,8 +131,9 @@ static bool timerfd_canceled(struct timerfd_ctx *ctx)
 
 static void timerfd_setup_cancel(struct timerfd_ctx *ctx, int flags)
 {
-	if (ctx->clockid == CLOCK_REALTIME && (flags & TFD_TIMER_ABSTIME) &&
-	    (flags & TFD_TIMER_CANCEL_ON_SET)) {
+	if ((ctx->clockid == CLOCK_REALTIME ||
+	     ctx->clockid == CLOCK_REALTIME_ALARM) &&
+	    (flags & TFD_TIMER_ABSTIME) && (flags & TFD_TIMER_CANCEL_ON_SET)) {
 		if (!ctx->might_cancel) {
 			ctx->might_cancel = true;
 			spin_lock(&cancel_lock);
@@ -124,7 +149,11 @@ static ktime_t timerfd_get_remaining(struct timerfd_ctx *ctx)
 {
 	ktime_t remaining;
 
-	remaining = hrtimer_expires_remaining(&ctx->tmr);
+	if (isalarm(ctx))
+		remaining = alarm_expires_remaining(&ctx->t.alarm);
+	else
+		remaining = hrtimer_expires_remaining(&ctx->t.tmr);
+
 	return remaining.tv64 < 0 ? ktime_set(0, 0): remaining;
 }
 
@@ -142,11 +171,28 @@ static int timerfd_setup(struct timerfd_ctx *ctx, int flags,
 	ctx->expired = 0;
 	ctx->ticks = 0;
 	ctx->tintv = timespec_to_ktime(ktmr->it_interval);
-	hrtimer_init(&ctx->tmr, clockid, htmode);
-	hrtimer_set_expires(&ctx->tmr, texp);
-	ctx->tmr.function = timerfd_tmrproc;
+
+	if (isalarm(ctx)) {
+		alarm_init(&ctx->t.alarm,
+			   ctx->clockid == CLOCK_REALTIME_ALARM ?
+			   ALARM_REALTIME : ALARM_BOOTTIME,
+			   timerfd_alarmproc);
+	} else {
+		hrtimer_init(&ctx->t.tmr, clockid, htmode);
+		hrtimer_set_expires(&ctx->t.tmr, texp);
+		ctx->t.tmr.function = timerfd_tmrproc;
+	}
+
 	if (texp.tv64 != 0) {
-		hrtimer_start(&ctx->tmr, texp, htmode);
+		if (isalarm(ctx)) {
+			if (flags & TFD_TIMER_ABSTIME)
+				alarm_start(&ctx->t.alarm, texp);
+			else
+				alarm_start_relative(&ctx->t.alarm, texp);
+		} else {
+			hrtimer_start(&ctx->t.tmr, texp, htmode);
+		}
+
 		if (timerfd_canceled(ctx))
 			return -ECANCELED;
 	}
@@ -158,7 +204,11 @@ static int timerfd_release(struct inode *inode, struct file *file)
 	struct timerfd_ctx *ctx = file->private_data;
 
 	timerfd_remove_cancel(ctx);
-	hrtimer_cancel(&ctx->tmr);
+
+	if (isalarm(ctx))
+		alarm_cancel(&ctx->t.alarm);
+	else
+		hrtimer_cancel(&ctx->t.tmr);
 	kfree_rcu(ctx, rcu);
 	return 0;
 }
@@ -215,9 +265,15 @@ static ssize_t timerfd_read(struct file *file, char __user *buf, size_t count,
 			 * callback to avoid DoS attacks specifying a very
 			 * short timer period.
 			 */
-			ticks += hrtimer_forward_now(&ctx->tmr,
-						     ctx->tintv) - 1;
-			hrtimer_restart(&ctx->tmr);
+			if (isalarm(ctx)) {
+				ticks += alarm_forward_now(
+					&ctx->t.alarm, ctx->tintv) - 1;
+				alarm_restart(&ctx->t.alarm);
+			} else {
+				ticks += hrtimer_forward_now(&ctx->t.tmr,
+							     ctx->tintv) - 1;
+				hrtimer_restart(&ctx->t.tmr);
+			}
 		}
 		ctx->expired = 0;
 		ctx->ticks = 0;
@@ -259,7 +315,9 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 
 	if ((flags & ~TFD_CREATE_FLAGS) ||
 	    (clockid != CLOCK_MONOTONIC &&
-	     clockid != CLOCK_REALTIME))
+	     clockid != CLOCK_REALTIME &&
+	     clockid != CLOCK_REALTIME_ALARM &&
+	     clockid != CLOCK_BOOTTIME_ALARM))
 		return -EINVAL;
 
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
@@ -268,7 +326,15 @@ SYSCALL_DEFINE2(timerfd_create, int, clockid, int, flags)
 
 	init_waitqueue_head(&ctx->wqh);
 	ctx->clockid = clockid;
-	hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
+
+	if (isalarm(ctx))
+		alarm_init(&ctx->t.alarm,
+			   ctx->clockid == CLOCK_REALTIME_ALARM ?
+			   ALARM_REALTIME : ALARM_BOOTTIME,
+			   timerfd_alarmproc);
+	else
+		hrtimer_init(&ctx->t.tmr, clockid, HRTIMER_MODE_ABS);
+
 	ctx->moffs = ktime_get_monotonic_offset();
 
 	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
@@ -305,8 +371,14 @@ static int do_timerfd_settime(int ufd, int flags,
 	 */
 	for (;;) {
 		spin_lock_irq(&ctx->wqh.lock);
-		if (hrtimer_try_to_cancel(&ctx->tmr) >= 0)
-			break;
+
+		if (isalarm(ctx)) {
+			if (alarm_try_to_cancel(&ctx->t.alarm) >= 0)
+				break;
+		} else {
+			if (hrtimer_try_to_cancel(&ctx->t.tmr) >= 0)
+				break;
+		}
 		spin_unlock_irq(&ctx->wqh.lock);
 		cpu_relax();
 	}
@@ -317,8 +389,12 @@ static int do_timerfd_settime(int ufd, int flags,
 	 * We do not update "ticks" and "expired" since the timer will be
 	 * re-programmed again in the following timerfd_setup() call.
 	 */
-	if (ctx->expired && ctx->tintv.tv64)
-		hrtimer_forward_now(&ctx->tmr, ctx->tintv);
+	if (ctx->expired && ctx->tintv.tv64) {
+		if (isalarm(ctx))
+			alarm_forward_now(&ctx->t.alarm, ctx->tintv);
+		else
+			hrtimer_forward_now(&ctx->t.tmr, ctx->tintv);
+	}
 
 	old->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 	old->it_interval = ktime_to_timespec(ctx->tintv);
@@ -345,9 +421,18 @@ static int do_timerfd_gettime(int ufd, struct itimerspec *t)
 	spin_lock_irq(&ctx->wqh.lock);
 	if (ctx->expired && ctx->tintv.tv64) {
 		ctx->expired = 0;
-		ctx->ticks +=
-			hrtimer_forward_now(&ctx->tmr, ctx->tintv) - 1;
-		hrtimer_restart(&ctx->tmr);
+
+		if (isalarm(ctx)) {
+			ctx->ticks +=
+				alarm_forward_now(
+					&ctx->t.alarm, ctx->tintv) - 1;
+			alarm_restart(&ctx->t.alarm);
+		} else {
+			ctx->ticks +=
+				hrtimer_forward_now(&ctx->t.tmr, ctx->tintv)
+				- 1;
+			hrtimer_restart(&ctx->t.tmr);
+		}
 	}
 	t->it_value = ktime_to_timespec(timerfd_get_remaining(ctx));
 	t->it_interval = ktime_to_timespec(ctx->tintv);
-- 
1.8.2.1

Re: [PATCH 1/2] alarmtimer: add functions for timerfd support

[John Stultz]

On 05/15/2013 02:38 PM, Todd Poynor wrote:
> 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>

Acked-by: John Stultz <john.stultz@linaro.org>

I'll queue this in my tree for 3.11, but I need to sort out which path 
the timerfd code needs to go upstream.

thanks
-john

Re: [PATCH 2/2] timerfd: add alarm timers

[John Stultz]

On 05/15/2013 02:38 PM, Todd Poynor wrote:
> Add support for clocks CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM,
> thereby enabling wakeup alarm timers via file descriptors.
>
> Signed-off-by: Todd Poynor <toddpoynor@google.com>

This all looks great to me and has been on my own todo list for awhile.

As I said, I'll queue the alarmtimer changes, and if I can get some acks 
from the fs folks, I'd be happy to queue the timerfd changes.

thanks
-john

Re: [PATCH 2/2] timerfd: add alarm timers

[John Stultz]

On 05/15/2013 02:51 PM, John Stultz wrote:
> On 05/15/2013 02:38 PM, Todd Poynor wrote:
>> Add support for clocks CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM,
>> thereby enabling wakeup alarm timers via file descriptors.
>>
>> Signed-off-by: Todd Poynor <toddpoynor@google.com>
>
> This all looks great to me and has been on my own todo list for awhile.
>
> As I said, I'll queue the alarmtimer changes, and if I can get some 
> acks from the fs folks, I'd be happy to queue the timerfd changes.
>

Ping? Any fsdevel folks mind taking a look at this?

Or maybe to turn this around, are there any objections to this change 
going in via tip/timers/core?

thanks
-john