Support setting and retrieving route MTU/AdvMSS

Author: vishvananda

nl/nl_linux.go

@@ -278,6 +278,11 @@ func NewRtAttrChild(parent *RtAttr, attrType int, data []byte) *RtAttr {
 	return attr
 }
 
+// AddChild adds an existing RtAttr as a child.
+func (a *RtAttr) AddChild(attr *RtAttr) {
+	a.children = append(a.children, attr)
+}
+
 func (a *RtAttr) Len() int {
 	if len(a.children) == 0 {
 		return (unix.SizeofRtAttr + len(a.Data))

route.go

@@ -45,6 +45,8 @@ type Route struct {
 	MPLSDst    *int
 	NewDst     Destination
 	Encap      Encap
+	MTU        int
+	AdvMSS     int
 }
 
 func (r Route) String() string {

route_linux.go

@@ -454,6 +454,25 @@ func (h *Handle) routeHandle(route *Route, req *nl.NetlinkRequest, msg *nl.RtMsg
 		msg.Type = uint8(route.Type)
 	}
 
+	var metrics []*nl.RtAttr
+	// TODO: support other rta_metric values
+	if route.MTU > 0 {
+		b := nl.Uint32Attr(uint32(route.MTU))
+		metrics = append(metrics, nl.NewRtAttr(unix.RTAX_MTU, b))
+	}
+	if route.AdvMSS > 0 {
+		b := nl.Uint32Attr(uint32(route.AdvMSS))
+		metrics = append(metrics, nl.NewRtAttr(unix.RTAX_ADVMSS, b))
+	}
+
+	if metrics != nil {
+		attr := nl.NewRtAttr(unix.RTA_METRICS, nil)
+		for _, metric := range metrics {
+			attr.AddChild(metric)
+		}
+		rtAttrs = append(rtAttrs, attr)
+	}
+
 	msg.Flags = uint32(route.Flags)
 	msg.Scope = uint8(route.Scope)
 	msg.Family = uint8(family)
@@ -685,6 +704,19 @@ func deserializeRoute(m []byte) (Route, error) {
 			encapType = attr
 		case nl.RTA_ENCAP:
 			encap = attr
+		case unix.RTA_METRICS:
+			metrics, err := nl.ParseRouteAttr(attr.Value)
+			if err != nil {
+				return route, err
+			}
+			for _, metric := range metrics {
+				switch metric.Attr.Type {
+				case unix.RTAX_MTU:
+					route.MTU = int(native.Uint32(metric.Value[0:4]))
+				case unix.RTAX_ADVMSS:
+					route.AdvMSS = int(native.Uint32(metric.Value[0:4]))
+				}
+			}
 		}
 	}
 

route_test.go

@@ -904,3 +904,57 @@ func TestSEG6RouteAddDel(t *testing.T) {
 		t.Fatal("SEG6 routes not removed properly")
 	}
 }
+
+func TestMTURouteAddDel(t *testing.T) {
+	_, err := RouteList(nil, FAMILY_V4)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	// get loopback interface
+	link, err := LinkByName("lo")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// bring the interface up
+	if err := LinkSetUp(link); err != nil {
+		t.Fatal(err)
+	}
+
+	// add a gateway route
+	dst := &net.IPNet{
+		IP:   net.IPv4(192, 168, 0, 0),
+		Mask: net.CIDRMask(24, 32),
+	}
+
+	route := Route{LinkIndex: link.Attrs().Index, Dst: dst, MTU: 500}
+	if err := RouteAdd(&route); err != nil {
+		t.Fatal(err)
+	}
+	routes, err := RouteList(link, FAMILY_V4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(routes) != 1 {
+		t.Fatal("Route not added properly")
+	}
+
+	if route.MTU != routes[0].MTU {
+		t.Fatal("Route mtu not set properly")
+	}
+
+	if err := RouteDel(&route); err != nil {
+		t.Fatal(err)
+	}
+	routes, err = RouteList(link, FAMILY_V4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(routes) != 0 {
+		t.Fatal("Route not removed properly")
+	}
+}