From 8dbd2b1f2a4aa039c8f6edd1534bf6dea25f7cef Mon Sep 17 00:00:00 2001
From: Avery Pennarun <apenwarr@gmail.com>
Date: Tue, 29 May 2012 04:20:19 -0400
Subject: [PATCH 3/6] Fix two bugs preventing DNS re-resolution if resolv.conf
 changes.

First, don't call res_init(); it forces libresolv to do a one-time name
resolution and save the settings forever (at least in uClibc).  If
/etc/resolv.conf doesn't exist at program startup time, this would guarantee
all future DNS requests would fail.

Second, change error_interval() to use a backoff instead of a hardcoded
"very long time plus randomness" timeout.  The default timeout to retry
initial DNS was 600 seconds, which was *way* too long.  Now we start at 2
seconds and work our way up.
---
 ntp.c  |   13 ++++++++++---
 ntpd.c |    7 ++++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/ntp.c b/ntp.c
index ac94638..9f83f1a 100644
--- a/ntp.c
+++ b/ntp.c
@@ -539,10 +539,17 @@ scale_interval(time_t requested)
 time_t
 error_interval(void)
 {
-	time_t interval, r;
+	static time_t step = 1;
+	time_t interval, maxival, r;
 
-	interval = INTERVAL_QUERY_PATHETIC * QSCALE_OFF_MAX / QSCALE_OFF_MIN;
-	r = arc4random() % (interval / 10);
+	maxival = INTERVAL_QUERY_PATHETIC * QSCALE_OFF_MAX / QSCALE_OFF_MIN;
+	interval = step * step / 2 + 1;  /* quadratic backoff timer */
+	if (interval > maxival)
+		interval = maxival;
+	else
+		step++;
+	r = arc4random() % (interval / 10 + 1);
+	log_info("retrying in %d", interval + r);
 	return (interval + r);
 }
 
diff --git a/ntpd.c b/ntpd.c
index 37dd862..22db996 100644
--- a/ntpd.c
+++ b/ntpd.c
@@ -100,7 +100,12 @@ main(int argc, char *argv[])
 	bzero(&conf, sizeof(conf));
 
 	log_init(1);		/* log to stderr until daemonized */
-	res_init();		/* XXX */
+
+	/* apenwarr: don't call res_init() here, as it prevents auto-rereading
+	 * of resolv.conf later (at least in uClibc).  I don't see any
+	 * advantage to it anyway.  And it had a fishy-looking XXX comment.
+	 */
+	//res_init();		/* XXX */
 
 
 	while ((ch = getopt(argc, argv, "b:df:sSw:")) != -1) {
-- 
1.7.7.3