From 5dbfa43f65ba09a5e06e8c58771f432b58882eed Mon Sep 17 00:00:00 2001
From: "Andrey V. Elsukov" <ae@FreeBSD.org>
Date: Tue, 9 Sep 2014 10:52:50 +0000
Subject: [PATCH] Add the ability to set `prefer_source' flag to an IPv6
 address. It affects the IPv6 source address selection algorithm (RFC 6724)
 and allows override the last rule ("longest matching prefix") for choosing
 among equivalent addresses. The address with `prefer_source' will be
 preferred source address.

Obtained from:	Yandex LLC
MFC after:	1 month
Sponsored by:	Yandex LLC
---
 sbin/ifconfig/af_inet6.c |  4 ++++
 sbin/ifconfig/ifconfig.8 | 15 ++++++++++++++-
 sys/netinet6/in6_src.c   | 10 ++++++++++
 sys/netinet6/in6_var.h   |  1 +
 usr.bin/netstat/inet6.c  |  2 +-
 5 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/sbin/ifconfig/af_inet6.c b/sbin/ifconfig/af_inet6.c
index d2e65e4dc96f..0f8688a8b3e1 100644
--- a/sbin/ifconfig/af_inet6.c
+++ b/sbin/ifconfig/af_inet6.c
@@ -254,6 +254,8 @@ in6_status(int s __unused, const struct ifaddrs *ifa)
 		printf("autoconf ");
 	if ((flags6 & IN6_IFF_TEMPORARY) != 0)
 		printf("temporary ");
+	if ((flags6 & IN6_IFF_PREFER_SOURCE) != 0)
+		printf("prefer_source ");
 
 	if (((struct sockaddr_in6 *)(ifa->ifa_addr))->sin6_scope_id)
 		printf("scopeid 0x%x ",
@@ -465,6 +467,8 @@ static struct cmd inet6_cmds[] = {
 	DEF_CMD("-deprecated", -IN6_IFF_DEPRECATED,	setip6flags),
 	DEF_CMD("autoconf",	IN6_IFF_AUTOCONF,	setip6flags),
 	DEF_CMD("-autoconf",	-IN6_IFF_AUTOCONF,	setip6flags),
+	DEF_CMD("prefer_source",IN6_IFF_PREFER_SOURCE,	setip6flags),
+	DEF_CMD("-prefer_source",-IN6_IFF_PREFER_SOURCE,setip6flags),
 	DEF_CMD("accept_rtadv",	ND6_IFF_ACCEPT_RTADV,	setnd6flags),
 	DEF_CMD("-accept_rtadv",-ND6_IFF_ACCEPT_RTADV,	setnd6flags),
 	DEF_CMD("no_radr",	ND6_IFF_NO_RADR,	setnd6flags),
diff --git a/sbin/ifconfig/ifconfig.8 b/sbin/ifconfig/ifconfig.8
index 5bf590d047d6..69e13ae0eabd 100644
--- a/sbin/ifconfig/ifconfig.8
+++ b/sbin/ifconfig/ifconfig.8
@@ -28,7 +28,7 @@
 .\"     From: @(#)ifconfig.8	8.3 (Berkeley) 1/5/94
 .\" $FreeBSD$
 .\"
-.Dd June 5, 2014
+.Dd September 9, 2014
 .Dt IFCONFIG 8
 .Os
 .Sh NAME
@@ -689,6 +689,19 @@ Clear a flag
 .Cm no_prefer_iface .
 .El
 .Pp
+The following parameters are specific for IPv6 addresses.
+Note that the address family keyword
+.Dq Li inet6
+is needed for them:
+.Bl -tag -width indent
+.It Cm prefer_source
+Set a flag to prefer address as a candidate of the source address for
+outgoing packets.
+.It Cm -prefer_source
+Clear a flag
+.Cm prefer_source .
+.El
+.Pp
 The following parameters are specific to cloning
 IEEE 802.11 wireless interfaces with the
 .Cm create
diff --git a/sys/netinet6/in6_src.c b/sys/netinet6/in6_src.c
index 34fa0801354b..9e163da8a41d 100644
--- a/sys/netinet6/in6_src.c
+++ b/sys/netinet6/in6_src.c
@@ -451,6 +451,16 @@ in6_selectsrc(struct sockaddr_in6 *dstsock, struct ip6_pktopts *opts,
 		if (ifa_preferred(&ia->ia_ifa, &ia_best->ia_ifa))
 			NEXT(9);
 
+		/*
+		 * Rule 10: prefer address with `prefer_source' flag.
+		 */
+		if ((ia_best->ia6_flags & IN6_IFF_PREFER_SOURCE) == 0 &&
+		    (ia->ia6_flags & IN6_IFF_PREFER_SOURCE) != 0)
+			REPLACE(10);
+		if ((ia_best->ia6_flags & IN6_IFF_PREFER_SOURCE) != 0 &&
+		    (ia->ia6_flags & IN6_IFF_PREFER_SOURCE) == 0)
+			NEXT(10);
+
 		/*
 		 * Rule 14: Use longest matching prefix.
 		 * Note: in the address selection draft, this rule is
diff --git a/sys/netinet6/in6_var.h b/sys/netinet6/in6_var.h
index 70e3a94025ba..5b74dca6bb61 100644
--- a/sys/netinet6/in6_var.h
+++ b/sys/netinet6/in6_var.h
@@ -498,6 +498,7 @@ struct	in6_rrenumreq {
 					 */
 #define IN6_IFF_AUTOCONF	0x40	/* autoconfigurable address. */
 #define IN6_IFF_TEMPORARY	0x80	/* temporary (anonymous) address. */
+#define	IN6_IFF_PREFER_SOURCE	0x0100	/* preferred address for SAS */
 #define IN6_IFF_NOPFX		0x8000	/* skip kernel prefix management.
 					 * XXX: this should be temporary.
 					 */
diff --git a/usr.bin/netstat/inet6.c b/usr.bin/netstat/inet6.c
index a44ff3ebf44f..96fdcaf6f7e3 100644
--- a/usr.bin/netstat/inet6.c
+++ b/usr.bin/netstat/inet6.c
@@ -346,7 +346,7 @@ static const char *srcrule_str[] = {
 	"public/temporary address",
 	"alive interface",
 	"better virtual status",
-	"rule #10",
+	"preferred source",
 	"rule #11",
 	"rule #12",
 	"rule #13",