From 11bbce7be6c86fd177ee903216ba43b8adba5e1f Mon Sep 17 00:00:00 2001
From: Avery Pennarun <apenwarr@gmail.com>
Date: Tue, 11 Jun 2013 00:26:19 -0400
Subject: Use error_interval() instead of QUERYTIME_MAX for each query packet.

The original implementation would wait QUERYTIME_MAX for each ntp request to
expire before *then* starting to count error_interval() seconds until the
next request.  This caused problems because the initial settime_timeout
could expire before even retrying a single time.  That, in turn, was
problematic if the first IP address in a multi-IP-address DNS entry turned
out not to work; we'd give up trying to set the time before we even tried
all the servers.

Now the retries are much faster (but still use the backoff interval).
---
 client.c |   12 ++++++------
 ntp.c    |    6 +++---
 ntpd.h   |    3 +--
 3 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/client.c b/client.c
index da6aa43..c0acaa2 100644
--- a/client.c
+++ b/client.c
@@ -118,7 +118,7 @@ client_query(struct ntp_peer *p)
 	int	tos = IPTOS_LOWDELAY;
 
 	if (p->addr == NULL && client_nextaddr(p) == -1) {
-		set_next(p, error_interval());
+		set_next(p, error_interval(0));
 		return (0);
 	}
 
@@ -136,7 +136,7 @@ client_query(struct ntp_peer *p)
 			    errno == EHOSTUNREACH) {
 				client_log_error(p, "connect", errno);
 				client_nextaddr(p);
-				set_next(p, error_interval());
+				set_next(p, error_interval(0));
 				return (-1);
 			} else
 				fatal("client_query connect");
@@ -171,7 +171,7 @@ client_query(struct ntp_peer *p)
 	}
 
 	p->state = STATE_QUERY_SENT;
-	set_deadline(p, QUERYTIME_MAX);
+	set_deadline(p, error_interval(0));
 
 	return (0);
 }
@@ -191,7 +191,7 @@ client_dispatch(struct ntp_peer *p, u_int8_t settime)
 		    errno == ENETUNREACH || errno == ENETDOWN ||
 		    errno == ECONNREFUSED || errno == EADDRNOTAVAIL) {
 			client_log_error(p, "recvfrom", errno);
-			set_next(p, error_interval());
+			set_next(p, error_interval(0));
 			return (0);
 		} else
 			fatal("recvfrom");
@@ -207,7 +207,7 @@ client_dispatch(struct ntp_peer *p, u_int8_t settime)
 
 	if ((msg.status & LI_ALARM) == LI_ALARM || msg.stratum == 0 ||
 	    msg.stratum > NTP_MAXSTRATUM) {
-		interval = error_interval();
+		interval = error_interval(0);
 		set_next(p, interval);
 		log_info("reply from %s: not synced, next query %ds",
 		    log_sockaddr((struct sockaddr *)&p->addr->ss), interval);
@@ -236,7 +236,7 @@ client_dispatch(struct ntp_peer *p, u_int8_t settime)
 	p->reply[p->shift].offset = ((T2 - T1) + (T3 - T4)) / 2;
 	p->reply[p->shift].delay = (T4 - T1) - (T3 - T2);
 	if (p->reply[p->shift].delay < 0) {
-		interval = error_interval();
+		interval = error_interval(0);
 		set_next(p, interval);
 		log_info("reply from %s: negative delay %f",
 		    log_sockaddr((struct sockaddr *)&p->addr->ss),
diff --git a/ntp.c b/ntp.c
index 4c33f7e..d8d14df 100644
--- a/ntp.c
+++ b/ntp.c
@@ -219,7 +219,7 @@ ntp_main(int pipe_prnt[2], struct ntpd_conf *nconf)
 			if (p->deadline > 0 && p->deadline < nextaction)
 				nextaction = p->deadline;
 			if (p->deadline > 0 && p->deadline <= time(NULL)) {
-				timeout = error_interval();
+				timeout = error_interval(1);
 				log_debug("no reply from %s received in time, "
 				    "next query %ds", log_sockaddr(
 				    (struct sockaddr *)&p->addr->ss), timeout);
@@ -542,7 +542,7 @@ scale_interval(time_t requested)
 }
 
 time_t
-error_interval(void)
+error_interval(int step_incr)
 {
 	static time_t step = 1;
 	time_t interval, maxival, r;
@@ -552,7 +552,7 @@ error_interval(void)
 	if (interval > maxival)
 		interval = maxival;
 	else
-		step++;
+		step += step_incr;
 	r = arc4random() % (interval / 10 + 1);
 	log_info("retrying in %d", interval + r);
 	return (interval + r);
diff --git a/ntpd.h b/ntpd.h
index 3bda1ec..e97c254 100644
--- a/ntpd.h
+++ b/ntpd.h
@@ -54,7 +54,6 @@
 #define	QSCALE_OFF_MIN			0.05
 #define	QSCALE_OFF_MAX			0.50
 
-#define	QUERYTIME_MAX		15	/* single query might take n secs max */
 #define	OFFSET_ARRAY_SIZE	8
 #define	SETTIME_MIN_OFFSET	10	/* min offset for settime at start */
 #define	SETTIME_TIMEOUT		15	/* max seconds to wait with -s */
@@ -251,7 +250,7 @@ int	client_dispatch(struct ntp_peer *, u_int8_t);
 void	client_log_error(struct ntp_peer *, const char *, int);
 void	update_scale(double);
 time_t	scale_interval(time_t);
-time_t	error_interval(void);
+time_t	error_interval(int step_incr);
 void	set_next(struct ntp_peer *, time_t);
 
 /* util.c */
-- 
1.7.9.dirty