commit c81e65ca38d0ea6fdf61d1fb08933d29282c0b71
Author: Ryota Ozaki <ozaki-r@iij.ad.jp>
Date:   Wed Feb 28 14:08:16 2018 +0900

    Let callout_reset and callout_schedule return if it reschedules a pending callout or not

diff --git a/share/man/man9/callout.9 b/share/man/man9/callout.9
index 29a099f59fc..0cc17a008f4 100644
--- a/share/man/man9/callout.9
+++ b/share/man/man9/callout.9
@@ -27,7 +27,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd November 21, 2014
+.Dd February 28, 2018
 .Dt CALLOUT 9
 .Os
 .Sh NAME
@@ -49,10 +49,10 @@
 .Fn "callout_init" "callout_t *c" "u_int flags"
 .Ft void
 .Fn "callout_destroy" "callout_t *c"
-.Ft void
+.Ft bool
 .Fn "callout_reset" "callout_t *c" "int ticks" \
     "void (*func)(void *)" "void *arg"
-.Ft void
+.Ft bool
 .Fn "callout_schedule" "callout_t *c" "int ticks"
 .Ft void
 .Fn "callout_setfunc" "callout_t *c" "void (*func)(void *)" "void *arg"
@@ -145,6 +145,9 @@ and
 and the
 .Em PENDING
 status is cleared.
+.Fn callout_reset
+returns true if it reschedules a pending callout with a newly specified
+time and returns false otherwise.
 .Pp
 The
 .Fn callout_setfunc
diff --git a/sys/kern/kern_timeout.c b/sys/kern/kern_timeout.c
index 02696442f37..add2c64171e 100644
--- a/sys/kern/kern_timeout.c
+++ b/sys/kern/kern_timeout.c
@@ -326,7 +326,7 @@ callout_destroy(callout_t *cs)
  *	already be set in the callout structure.  Must be called with
  *	callout_lock.
  */
-static void
+static bool
 callout_schedule_locked(callout_impl_t *c, kmutex_t *lock, int to_ticks)
 {
 	struct callout_cpu *cc, *occ;
@@ -353,7 +353,7 @@ callout_schedule_locked(callout_impl_t *c, kmutex_t *lock, int to_ticks)
 			CIRCQ_INSERT(&c->c_list, &occ->cc_todo);
 		}
 		mutex_spin_exit(lock);
-		return;
+		return true;
 	}
 
 	cc = curcpu()->ci_data.cpu_callout;
@@ -372,6 +372,7 @@ callout_schedule_locked(callout_impl_t *c, kmutex_t *lock, int to_ticks)
 		mutex_spin_exit(cc->cc_lock);
 	}
 	mutex_spin_exit(lock);
+	return false;
 }
 
 /*
@@ -380,7 +381,7 @@ callout_schedule_locked(callout_impl_t *c, kmutex_t *lock, int to_ticks)
  *	Reset a callout structure with a new function and argument, and
  *	schedule it to run.
  */
-void
+bool
 callout_reset(callout_t *cs, int to_ticks, void (*func)(void *), void *arg)
 {
 	callout_impl_t *c = (callout_impl_t *)cs;
@@ -392,7 +393,7 @@ callout_reset(callout_t *cs, int to_ticks, void (*func)(void *), void *arg)
 	lock = callout_lock(c);
 	c->c_func = func;
 	c->c_arg = arg;
-	callout_schedule_locked(c, lock, to_ticks);
+	return callout_schedule_locked(c, lock, to_ticks);
 }
 
 /*
@@ -401,7 +402,7 @@ callout_reset(callout_t *cs, int to_ticks, void (*func)(void *), void *arg)
  *	Schedule a callout to run.  The function and argument must
  *	already be set in the callout structure.
  */
-void
+bool
 callout_schedule(callout_t *cs, int to_ticks)
 {
 	callout_impl_t *c = (callout_impl_t *)cs;
@@ -410,7 +411,7 @@ callout_schedule(callout_t *cs, int to_ticks)
 	KASSERT(c->c_magic == CALLOUT_MAGIC);
 
 	lock = callout_lock(c);
-	callout_schedule_locked(c, lock, to_ticks);
+	return callout_schedule_locked(c, lock, to_ticks);
 }
 
 /*
diff --git a/sys/sys/callout.h b/sys/sys/callout.h
index 0214b21fb05..4c4ff2e4cf2 100644
--- a/sys/sys/callout.h
+++ b/sys/sys/callout.h
@@ -111,8 +111,8 @@ void	callout_hardclock(void);
 void	callout_init(callout_t *, u_int);
 void	callout_destroy(callout_t *);
 void	callout_setfunc(callout_t *, void (*)(void *), void *);
-void	callout_reset(callout_t *, int, void (*)(void *), void *);
-void	callout_schedule(callout_t *, int);
+bool	callout_reset(callout_t *, int, void (*)(void *), void *);
+bool	callout_schedule(callout_t *, int);
 bool	callout_stop(callout_t *);
 bool	callout_halt(callout_t *, void *);
 bool	callout_pending(callout_t *);