timerfd: Add alarm timers

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

1 files changed, 108 insertions, 23 deletions

diff --git a/fs/timerfd.c b/fs/timerfd.c
index 32b644f03690..929312180dd0 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);