ovsnl: only fail if no known families are found (#88)

Before this commit the ovnl client logic was such that it needs to be
kept in lock-step synchronization with a particular version of the
netlink interface. This is too fragile, as each new update requires
touching this logic, which in turn makes it non-backward compatible.

This commit flips the logic on its head and instead makes the client
complains only if no 'known' families are found. This makes the init
logic future proof and backward compatible.

Author: armando-migliaccio

ovsnl/client.go

@@ -80,32 +80,25 @@ func (c *Client) Close() error {
 
 // init initializes the generic netlink family service of Client.
 func (c *Client) init(families []genetlink.Family) error {
-	// Assume 5 families present.
 	var gotf int
-	const wantf = 5
 
 	for _, f := range families {
 		// Ignore any families without the OVS prefix.
 		if !strings.HasPrefix(f.Name, "ovs_") {
 			continue
 		}
-
-		gotf++
+		// Ignore any families that might be unknown.
 		if err := c.initFamily(f); err != nil {
-			return err
+			continue
 		}
+		gotf++
 	}
 
-	// No families; return error for os.IsNotExist check.
+	// No known families; return error for os.IsNotExist check.
 	if gotf == 0 {
 		return os.ErrNotExist
 	}
 
-	if gotf != wantf {
-		return fmt.Errorf("expected %d OVS generic netlink families, but found %d",
-			wantf, gotf)
-	}
-
 	return nil
 }
 
@@ -118,12 +111,10 @@ func (c *Client) initFamily(f genetlink.Family) error {
 			c: c,
 		}
 		return nil
-	case ovsh.FlowFamily, ovsh.PacketFamily, ovsh.VportFamily, ovsh.MeterFamily:
-		// TODO(mdlayher): populate.
-		return nil
+	default:
+		// Unknown OVS netlink family, nothing we can do.
+		return fmt.Errorf("unknown OVS generic netlink family: %q", f.Name)
 	}
-
-	return fmt.Errorf("unrecognized OVS generic netlink family: %q", f.Name)
 }
 
 // headerBytes converts an ovsh.Header into a byte slice.

ovsnl/client_linux_test.go

@@ -46,7 +46,7 @@ func TestClientNoFamiliesIsNotExist(t *testing.T) {
 	t.Logf("OK error: %v", err)
 }
 
-func TestClientInvalidFamily(t *testing.T) {
+func TestClientUnknownFamilies(t *testing.T) {
 	conn := genltest.Dial(func(greq genetlink.Message, nreq netlink.Message) ([]genetlink.Message, error) {
 		return familyMessages([]string{
 			"ovs_foo",
@@ -61,12 +61,10 @@ func TestClientInvalidFamily(t *testing.T) {
 	t.Logf("OK error: %v", err)
 }
 
-func TestClientMissingFamilies(t *testing.T) {
+func TestClientNoFamilies(t *testing.T) {
 	conn := genltest.Dial(func(greq genetlink.Message, nreq netlink.Message) ([]genetlink.Message, error) {
 		// Too few OVS families.
-		return familyMessages([]string{
-			ovsh.DatapathFamily,
-		}), nil
+		return nil, nil
 	})
 
 	_, err := newClient(conn)
@@ -77,14 +75,10 @@ func TestClientMissingFamilies(t *testing.T) {
 	t.Logf("OK error: %v", err)
 }
 
-func TestClientOK(t *testing.T) {
+func TestClientKnownFamilies(t *testing.T) {
 	conn := genltest.Dial(func(greq genetlink.Message, nreq netlink.Message) ([]genetlink.Message, error) {
 		return familyMessages([]string{
 			ovsh.DatapathFamily,
-			ovsh.FlowFamily,
-			ovsh.PacketFamily,
-			ovsh.VportFamily,
-			ovsh.MeterFamily,
 		}), nil
 	})