Document the ROUTE_FLAGFILTER socket option.

ok jmatthew@

1 files changed, 24 insertions, 2 deletions

diff --git a/share/man/man4/route.4 b/share/man/man4/route.4
index 03a47a7c289..5085487a1fb 100644
--- a/share/man/man4/route.4
+++ b/share/man/man4/route.4
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: route.4,v 1.54 2019/11/22 06:26:00 claudio Exp $
+.\"	$OpenBSD: route.4,v 1.55 2020/08/21 13:20:14 benno Exp $
 .\"	$NetBSD: route.4,v 1.3 1994/11/30 16:22:31 jtc Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
@@ -30,7 +30,7 @@
 .\"
 .\"     @(#)route.4	8.6 (Berkeley) 4/19/94
 .\"
-.Dd $Mdocdate: November 22 2019 $
+.Dd $Mdocdate: August 21 2020 $
 .Dt ROUTE 4
 .Os
 .Sh NAME
@@ -195,6 +195,15 @@ by doing a
 .Xr shutdown 2
 system call for further input.
 .Pp
+There are three filter options that can be used to restrict the received route messages
+to a subset of all the route messages processed by the kernel:
+.Pp
+.Bl -tag -width xxxxxxxx -compact
+.It ROUTE_TABLEFILTER
+.It ROUTE_MSGFILTER
+.It ROUTE_FLAGFILTER
+.El
+.Pp
 A process can specify an alternate routing table by using the
 .Dv ROUTE_TABLEFILTER
 .Xr setsockopt 2 .
@@ -244,6 +253,19 @@ if (setsockopt(routefd, AF_ROUTE, ROUTE_PRIOFILTER,
 	err(1, "setsockopt(ROUTE_PRIOFILTER)");
 .Ed
 .Pp
+The
+.Dv ROUTE_FLAGFILTER
+socket option can be used to exclude a subset of
+.Vt rtm_flags
+flags from the received route messages:
+.Bd -literal -offset indent
+int rtfilter = RTF_LLINFO | RTF_BROADCAST;
+
+if (setsockopt(routefd, AF_ROUTE, ROUTE_FLAGFILTER, &rtfilter,
+    sizeof(rtfilter)) == -1)
+	err(1, "setsockopt(ROUTE_FLAGFILTER)");
+.Ed
+.Pp
 The predefined constants for the routing priorities are:
 .Bd -literal
 #define RTP_NONE	0	/* unset priority use sane default */