- Delayed-ack is now a compile-time option, compiled out by default.

This feature is simply too experimental for right now, and causes
  some problems to some failover installations.  We will revisit this
  in future releases.  [ISC-Bugs #18832]

RELNOTES

@@ -67,6 +67,11 @@ work on other platforms. Please report any problems and suggested fixes to
 
 - A bug cleaning up unknown-xxx temporary option definitions was fixed.
 
+- Delayed-ack is now a compile-time option, compiled out by default.
+  This feature is simply too experimental for right now, and causes
+  some problems to some failover installations.  We will revisit this
+  in future releases.
+
 			Changes since 4.1.0a1
 
 - Corrected list of failover state values in dhcpd man page.

configure.ac

@@ -91,6 +91,15 @@ if test "$enable_tracing" != "no" ; then
 		  [Define to include server activity tracing support.])
 fi
 
+# Delayed-ack feature support (experimental).
+AC_ARG_ENABLE(delayed_ack,
+	AC_HELP_STRING([--enable-delayed-ack],
+		       [queues multiple DHCPACK replies (default is no)]))
+if test "$enable_delayed_ack" = "yes"; then
+	AC_DEFINE([DELAYED_ACK], [1],
+		  [Define to queue multiple DHCPACK replies per fsync.])
+fi
+
 # DHCPv6 optional compile-time feature.
 AC_ARG_ENABLE(dhcpv6,
 	AC_HELP_STRING([--enable-dhcpv6],

server/dhcp.c

@@ -2424,15 +2424,30 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
 			packet -> raw -> chaddr,
 			sizeof packet -> raw -> chaddr); /* XXX */
 	} else {
+#if !defined(DELAYED_ACK)
+		/* Install the new information on 'lt' onto the lease at
+		 * 'lease'.  If this is a DHCPOFFER, it is a 'soft' promise,
+		 * if it is a DHCPACK, it is a 'hard' binding, so it needs
+		 * to be recorded and propogated immediately.  If the update
+		 * fails, don't ACK it (or BOOTREPLY) either; we may give
+		 * the same lease to another client later, and that would be
+		 * a conflict.
+		 */
+		if (!supersede_lease(lease, lt, !offer || (offer == DHCPACK),
+				     offer == DHCPACK, offer == DHCPACK)) {
+#else /* defined(DELAYED_ACK) */
 		/* Install the new information on 'lt' onto the lease at
 		 * 'lease'.  We will not 'commit' this information to disk
 		 * yet (fsync()), we will 'propogate' the information if
 		 * this is BOOTP or a DHCPACK, but we will not 'pimmediate'ly
 		 * transmit failover binding updates (this is delayed until
-		* after the fsync()).
+		 * after the fsync()).  If the update fails, don't ACK it (or
+		 * BOOTREPLY either); we may give the same lease out to a
+		 * different client, and that would be a conflict.
 		 */
 		if (!supersede_lease(lease, lt, 0, !offer || offer == DHCPACK,
 				     0)) {
+#endif
 			log_info ("%s: database update failed", msg);
 			free_lease_state (state, MDL);
 			lease_dereference (&lt, MDL);
@@ -2822,10 +2837,12 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
 		++outstanding_pings;
 	} else {
   		lease->cltt = cur_time;
+#if defined(DELAYED_ACK)
 		if (!(lease->flags & STATIC_LEASE) &&
 		    (!offer || (offer == DHCPACK)))
 			delayed_ack_enqueue(lease);
 		else 
+#endif
 			dhcp_reply(lease);
 	}
 }

server/dhcpd.conf.5

@@ -28,7 +28,7 @@
 .\" see ``http://www.vix.com''.   To learn more about Nominum, Inc., see
 .\" ``http://www.nominum.com''.
 .\"
-.\" $Id: dhcpd.conf.5,v 1.98 2008/10/22 11:41:58 fdupont Exp $
+.\" $Id: dhcpd.conf.5,v 1.99 2008/11/03 18:13:58 dhankins Exp $
 .\"
 .TH dhcpd.conf 5
 .SH NAME
@@ -2098,6 +2098,10 @@ Similarly, \fImicroseconds\fR indicates how many microseconds are permitted
 to pass inbetween queuing a packet pending an fsync, and performing the
 fsync.  Valid values range from 0 to 2^32-1, and defaults to 250,000 (1/4 of
 a second).
+.PP
+Please note that as delayed-ack is currently experimental, the delayed-ack
+feature is not compiled in by default, but must be enabled at compile time
+with './configure --enable-delayed-ack'.
 .RE
 .PP
 The

server/stables.c

@@ -239,8 +239,11 @@ static struct option server_options[] = {
 	{ "dhcpv6-pid-file-name", "t",		&server_universe,  55, 1 },
 	{ "limit-addrs-per-ia", "L",		&server_universe,  56, 1 },
 	{ "limit-prefs-per-ia", "L",		&server_universe,  57, 1 },
+/* Assert a configuration parsing error if delayed-ack isn't compiled in. */
+#if defined(DELAYED_ACK)
 	{ "delayed-ack", "S",			&server_universe,  58, 1 },
 	{ "max-ack-delay", "L",			&server_universe,  59, 1 },
+#endif
 	{ NULL, NULL, NULL, 0, 0 }
 };