Add sysctl net.inet.tcp.always_keepalive, when this is set the system

behaves as if SO_KEEPALIVE was set on all TCP sockets, forcing keepalives
to be sent every net.inet.tcp.keepidle half-seconds.

In conjunction with a keepidle value greatly reduced from the default,
this can be useful for keeping sessions open if you are stuck on a network
with short NAT or firewall timeouts.

Feedback from various people, ok henning@ claudio@

6 files changed, 25 insertions, 11 deletions

diff --git a/lib/libc/gen/sysctl.3 b/lib/libc/gen/sysctl.3
index 5fd5f847fee..fd04ac0dbfc 100644
--- a/lib/libc/gen/sysctl.3
+++ b/lib/libc/gen/sysctl.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: sysctl.3,v 1.203 2011/06/27 17:43:03 naddy Exp $
+.\"	$OpenBSD: sysctl.3,v 1.204 2011/07/06 23:44:20 sthen Exp $
 .\"
 .\" Copyright (c) 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -27,7 +27,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: June 27 2011 $
+.Dd $Mdocdate: July 6 2011 $
 .Dt SYSCTL 3
 .Os
 .Sh NAME
@@ -1575,6 +1575,10 @@ Time to keep alive the initial SYN packet of a TCP handshake.
 Time after a keepalive probe is sent until, in the absence of any response,
 another probe is sent.
 See also tcp.slowhz.
+.It Li tcp.always_keepalive
+Act as if the option
+.Dv SO_KEEPALIVE
+was set on all TCP sockets.
 .It Li tcp.mssdflt
 The maximum segment size that is used as default for non-local connections.
 The default value is 512.
diff --git a/sbin/sysctl/sysctl.8 b/sbin/sysctl/sysctl.8
index 238048037f5..6bb7064dba1 100644
--- a/sbin/sysctl/sysctl.8
+++ b/sbin/sysctl/sysctl.8
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: sysctl.8,v 1.159 2011/06/24 19:47:48 naddy Exp $
+.\"	$OpenBSD: sysctl.8,v 1.160 2011/07/06 23:44:20 sthen Exp $
 .\"	$NetBSD: sysctl.8,v 1.4 1995/09/30 07:12:49 thorpej Exp $
 .\"
 .\" Copyright (c) 1993
@@ -30,7 +30,7 @@
 .\"
 .\"	@(#)sysctl.8	8.2 (Berkeley) 5/9/95
 .\"
-.Dd $Mdocdate: June 24 2011 $
+.Dd $Mdocdate: July 6 2011 $
 .Dt SYSCTL 8
 .Os
 .Sh NAME
@@ -257,6 +257,7 @@ and a few require a kernel compiled with non-standard
 .It net.inet.tcp.keepinittime	integer	yes
 .It net.inet.tcp.keepidle	integer	yes
 .It net.inet.tcp.keepintvl	integer	yes
+.It net.inet.tcp.always_keepalive	integer	yes
 .It net.inet.tcp.slowhz	integer	no
 .It net.inet.tcp.baddynamic	array	yes
 .It net.inet.tcp.sack	integer	yes
diff --git a/sys/netinet/tcp_timer.c b/sys/netinet/tcp_timer.c
index a1dd72aae79..7f2511d751a 100644
--- a/sys/netinet/tcp_timer.c
+++ b/sys/netinet/tcp_timer.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_timer.c,v 1.45 2010/07/03 04:44:51 guenther Exp $	*/
+/*	$OpenBSD: tcp_timer.c,v 1.46 2011/07/06 23:44:20 sthen Exp $	*/
 /*	$NetBSD: tcp_timer.c,v 1.14 1996/02/13 23:44:09 christos Exp $	*/
 
 /*
@@ -55,6 +55,7 @@
 #include <netinet/ip_icmp.h>
 #include <netinet/tcp_seq.h>
 
+int	tcp_always_keepalive;
 int	tcp_keepidle;
 int	tcp_keepintvl;
 int	tcp_maxpersistidle;	/* max idle time in persist */
@@ -435,7 +436,8 @@ tcp_timer_keep(void *arg)
 	tcpstat.tcps_keeptimeo++;
 	if (TCPS_HAVEESTABLISHED(tp->t_state) == 0)
 		goto dropit;
-	if (tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE &&
+	if ((tcp_always_keepalive ||
+	    tp->t_inpcb->inp_socket->so_options & SO_KEEPALIVE) &&
 	    tp->t_state <= TCPS_CLOSING) {
 		if ((tcp_maxidle > 0) &&
 		    ((tcp_now - tp->t_rcvtime) >= tcp_keepidle + tcp_maxidle))
diff --git a/sys/netinet/tcp_timer.h b/sys/netinet/tcp_timer.h
index 6f0dceda02a..67daccdfb32 100644
--- a/sys/netinet/tcp_timer.h
+++ b/sys/netinet/tcp_timer.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_timer.h,v 1.12 2008/11/08 12:54:58 dlg Exp $	*/
+/*	$OpenBSD: tcp_timer.h,v 1.13 2011/07/06 23:44:20 sthen Exp $	*/
 /*	$NetBSD: tcp_timer.h,v 1.6 1995/03/26 20:32:37 jtc Exp $	*/
 
 /*
@@ -145,6 +145,7 @@ typedef void (*tcp_timer_func_t)(void *);
 extern const tcp_timer_func_t tcp_timer_funcs[TCPT_NTIMERS];
 
 extern int tcptv_keep_init;
+extern int tcp_always_keepalive;	/* assume SO_KEEPALIVE is always set */
 extern int tcp_keepidle;		/* time before keepalive probes begin */
 extern int tcp_keepintvl;		/* time between keepalive probes */
 extern int tcp_maxidle;			/* time to drop after starting probes */
diff --git a/sys/netinet/tcp_usrreq.c b/sys/netinet/tcp_usrreq.c
index 2e14907f448..6f70aaf3184 100644
--- a/sys/netinet/tcp_usrreq.c
+++ b/sys/netinet/tcp_usrreq.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_usrreq.c,v 1.107 2011/04/28 09:56:27 claudio Exp $	*/
+/*	$OpenBSD: tcp_usrreq.c,v 1.108 2011/07/06 23:44:20 sthen Exp $	*/
 /*	$NetBSD: tcp_usrreq.c,v 1.20 1996/02/13 23:44:16 christos Exp $	*/
 
 /*
@@ -909,6 +909,10 @@ tcp_sysctl(name, namelen, oldp, oldlenp, newp, newlen)
 	case TCPCTL_DROP:
 		return (tcp_ident(oldp, oldlenp, newp, newlen, 1));
 
+	case TCPCTL_ALWAYS_KEEPALIVE:
+		return (sysctl_int(oldp, oldlenp, newp, newlen,
+		    &tcp_always_keepalive));
+
 #ifdef TCP_ECN
 	case TCPCTL_ECN:
 		return (sysctl_int(oldp, oldlenp, newp, newlen,
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index 0573c7d966b..7a61253231f 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: tcp_var.h,v 1.98 2011/01/07 17:50:42 bluhm Exp $	*/
+/*	$OpenBSD: tcp_var.h,v 1.99 2011/07/06 23:44:20 sthen Exp $	*/
 /*	$NetBSD: tcp_var.h,v 1.17 1996/02/13 23:44:24 christos Exp $	*/
 
 /*
@@ -473,7 +473,8 @@ struct	tcpstat {
 #define	TCPCTL_DROP	       19 /* drop tcp connection */
 #define	TCPCTL_SACKHOLE_LIMIT  20 /* max entries for tcp sack queues */
 #define	TCPCTL_STATS	       21 /* TCP statistics */
-#define	TCPCTL_MAXID	       22
+#define	TCPCTL_ALWAYS_KEEPALIVE 22 /* assume SO_KEEPALIVE is always set */
+#define	TCPCTL_MAXID	       23
 
 #define	TCPCTL_NAMES { \
 	{ 0, 0 }, \
@@ -497,7 +498,8 @@ struct	tcpstat {
 	{ "reasslimit", 	CTLTYPE_INT }, \
 	{ "drop", 	CTLTYPE_STRUCT }, \
 	{ "sackholelimit", 	CTLTYPE_INT }, \
-	{ "stats",	CTLTYPE_STRUCT } \
+	{ "stats",	CTLTYPE_STRUCT }, \
+	{ "always_keepalive",	CTLTYPE_INT } \
 }
 
 #define	TCPCTL_VARS { \