Add support for setting nexthop flags for routes

There are few nexthop flags that are usable in some scenarios: onlink
and pervasive. This patch allows to set, clear and list them.

route.go

@@ -17,6 +17,13 @@ const (
 	SCOPE_NOWHERE  Scope = syscall.RT_SCOPE_NOWHERE
 )
 
+type NextHopFlag int
+
+const (
+	FLAG_ONLINK    NextHopFlag = syscall.RTNH_F_ONLINK
+	FLAG_PERVASIVE NextHopFlag = syscall.RTNH_F_PERVASIVE
+)
+
 // Route represents a netlink route. A route is associated with a link,
 // has a destination network, an optional source ip, and optional
 // gateway. Advanced route parameters and non-main routing tables are
@@ -27,11 +34,40 @@ type Route struct {
 	Dst       *net.IPNet
 	Src       net.IP
 	Gw        net.IP
+	Flags     int
 }
 
 func (r Route) String() string {
-	return fmt.Sprintf("{Ifindex: %d Dst: %s Src: %s Gw: %s}", r.LinkIndex, r.Dst,
-		r.Src, r.Gw)
+	return fmt.Sprintf("{Ifindex: %d Dst: %s Src: %s Gw: %s Flags: %s}", r.LinkIndex, r.Dst,
+		r.Src, r.Gw, r.ListFlags())
+}
+
+func (r *Route) SetFlag(flag NextHopFlag) {
+	r.Flags |= int(flag)
+}
+
+func (r *Route) ClearFlag(flag NextHopFlag) {
+	r.Flags &^= int(flag)
+}
+
+type flagString struct {
+	f NextHopFlag
+	s string
+}
+
+var testFlags = []flagString{
+	flagString{f: FLAG_ONLINK, s: "onlink"},
+	flagString{f: FLAG_PERVASIVE, s: "pervasive"},
+}
+
+func (r *Route) ListFlags() []string {
+	var flags []string
+	for _, tf := range testFlags {
+		if r.Flags&int(tf.f) != 0 {
+			flags = append(flags, tf.s)
+		}
+	}
+	return flags
 }
 
 // RouteUpdate is sent when a route changes - type is RTM_NEWROUTE or RTM_DELROUTE

route_linux.go

@@ -30,6 +30,7 @@ func routeHandle(route *Route, req *nl.NetlinkRequest, msg *nl.RtMsg) error {
 	}
 
 	msg.Scope = uint8(route.Scope)
+	msg.Flags = uint32(route.Flags)
 	family := -1
 	var rtAttrs []*nl.RtAttr
 
@@ -155,6 +156,7 @@ func deserializeRoute(m []byte) (Route, error) {
 		return route, err
 	}
 	route.Scope = Scope(msg.Scope)
+	route.Flags = int(msg.Flags)
 
 	native := nl.NativeEndian()
 	for _, attr := range attrs {