Merge support for Routing Policy Database (RPDB)

This can be used for multi-homed connections and other advanced routing
in Linux. See the documentation links for more information about doing
this in linux.

The code was a originally pure addon into the conf.d/net files, written
in mid-2004 for doing multi-homing between two internet connections. I
have finally cleaned this up and integrated it. Thanks to Jonathan Kwan
for giving me the original impetus to develop this for Gentoo (it was
his dual internet connections...).

In the intervening years, it was a example of postup/postdown in the
net.example file, however that suffered from a few corner case issues.

If you were using the code from net.example, please see the updated
section 'Advanced Routing' on syntax, and drop your old function blocks.
Additionally, note that the rules added are now directly saved for
removal when the interface is taken down.

net/iproute2.sh

@@ -199,6 +199,32 @@ _tunnel()
 	ip tunnel "$@"
 }
 
+# This is just to trim whitespace, do not add any quoting!
+_trim() {
+	echo $*
+}
+
+# This is our interface to Routing Policy Database RPDB
+# This allows for advanced routing tricks
+_ip_rule_runner() {
+	local cmd rules OIFS="${IFS}"
+	cmd="$1"
+	rules="$2"
+	eindent
+	local IFS="$__IFS"
+	for ru in $rules ; do
+		unset IFS
+		ruN="$(trim "${ru}")"
+		[ -z "${ruN}" ] && continue
+		ebegin "${cmd} ${ruN}"
+		ip rule ${cmd} ${ru}
+		eend $?
+		local IFS="$__IFS"
+	done
+	IFS="${OIFS}"
+	eoutdent
+}
+
 iproute2_pre_start()
 {
 	local tunnel=
@@ -210,7 +236,7 @@ iproute2_pre_start()
 		ebegin "Creating tunnel ${IFVAR}"
 		ip tunnel add ${tunnel} name "${IFACE}"
 		eend $? || return 1
-		_up	
+		_up
 	fi
 
 	# MTU support
@@ -240,6 +266,15 @@ iproute2_post_start()
 
 	# Kernel may not have IP built in
 	if [ -e /proc/net/route ]; then
+		local rules="$(_get_array "rules_${IFVAR}")"
+		if [ -n "${rules}" ]; then
+			if ! ip rule list | grep -q "^"; then
+				eerror "IP Policy Routing (CONFIG_IP_MULTIPLE_TABLES) needed for ip rule"
+			else
+				service_set_value "ip_rule" "${rules}"
+				_ip_rule_runner add "${rules}"
+			fi
+		fi
 		ip route flush table cache dev "${IFACE}"
 	fi
 
@@ -259,6 +294,13 @@ iproute2_post_start()
 
 iproute2_post_stop()
 {
+	# Kernel may not have IP built in
+	if [ -e /proc/net/route ]; then
+		local rules="$(service_get_value "ip_rule")"
+		[ -n "${rules}" ] && _ip_rule_runner del "${rules}"
+		ip route flush table cache dev "${IFACE}"
+	fi
+
 	# Don't delete sit0 as it's a special tunnel
 	if [ "${IFACE}" != "sit0" ]; then
 		if [ -n "$(ip tunnel show "${IFACE}" 2>/dev/null)" ]; then