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@

1 files changed, 6 insertions, 2 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.