add generic rate limiting support from netbsd; ratelimit is purely time based,

ppsratecheck is for controlling packets/second

Obtained from:	netbsd

sys/kern/kern_time.c

@@ -663,3 +663,91 @@ timevalfix(struct timeval *t1)
 		t1->tv_usec -= 1000000;
 	}
 }
+
+#ifndef timersub
+#define timersub(tvp, uvp, vvp)						\
+	do {								\
+		(vvp)->tv_sec = (tvp)->tv_sec - (uvp)->tv_sec;		\
+		(vvp)->tv_usec = (tvp)->tv_usec - (uvp)->tv_usec;	\
+		if ((vvp)->tv_usec < 0) {				\
+			(vvp)->tv_sec--;				\
+			(vvp)->tv_usec += 1000000;			\
+		}							\
+	} while (0)
+#endif
+
+/*
+ * ratecheck(): simple time-based rate-limit checking.  see ratecheck(9)
+ * for usage and rationale.
+ */
+int
+ratecheck(struct timeval *lasttime, const struct timeval *mininterval)
+{
+	struct timeval tv, delta;
+	int rv = 0;
+
+	getmicrouptime(&tv);
+	timersub(&tv, lasttime, &delta);
+
+	/*
+	 * check for 0,0 is so that the message will be seen at least once,
+	 * even if interval is huge.
+	 */
+	if (timevalcmp(&delta, mininterval, >=) ||
+	    (lasttime->tv_sec == 0 && lasttime->tv_usec == 0)) {
+		*lasttime = tv;
+		rv = 1;
+	}
+
+	return (rv);
+}
+
+/*
+ * ppsratecheck(): packets (or events) per second limitation.
+ */
+int
+ppsratecheck(struct timeval *lasttime, int *curpps, int maxpps)
+{
+	struct timeval tv, delta;
+	int rv;
+
+	getmicrouptime(&tv);
+	timersub(&tv, lasttime, &delta);
+
+	/*
+	 * check for 0,0 is so that the message will be seen at least once.
+	 * if more than one second have passed since the last update of
+	 * lasttime, reset the counter.
+	 *
+	 * we do increment *curpps even in *curpps < maxpps case, as some may
+	 * try to use *curpps for stat purposes as well.
+	 */
+	if ((lasttime->tv_sec == 0 && lasttime->tv_usec == 0) ||
+	    delta.tv_sec >= 1) {
+		*lasttime = tv;
+		*curpps = 0;
+		rv = 1;
+	} else if (maxpps < 0)
+		rv = 1;
+	else if (*curpps < maxpps)
+		rv = 1;
+	else
+		rv = 0;
+
+#if 1 /*DIAGNOSTIC?*/
+	/* be careful about wrap-around */
+	if (*curpps + 1 > *curpps)
+		*curpps = *curpps + 1;
+#else
+	/*
+	 * assume that there's not too many calls to this function.
+	 * not sure if the assumption holds, as it depends on *caller's*
+	 * behavior, not the behavior of this function.
+	 * IMHO it is wrong to make assumption on the caller's behavior,
+	 * so the above #if is #if 1, not #ifdef DIAGNOSTIC.
+	 */
+	*curpps = *curpps + 1;
+#endif
+
+	return (rv);
+}

sys/sys/time.h

@@ -302,6 +302,8 @@ void	getmicrotime(struct timeval *tvp);
 /* Other functions */
 int	itimerdecr(struct itimerval *itp, int usec);
 int	itimerfix(struct timeval *tv);
+int	ppsratecheck(struct timeval *, int *, int);
+int	ratecheck(struct timeval *, const struct timeval *);
 void	timevaladd(struct timeval *t1, struct timeval *t2);
 void	timevalsub(struct timeval *t1, struct timeval *t2);
 int	tvtohz(struct timeval *tv);