Fixed rtnetlink attributes packaging into netlink message.

I've also added NetworkLinkDel() function which allows deleting
of the existing network links.

Docker-DCO-1.1-Signed-off-by: Milos Gajdos <milosgajdos83@gmail.com> (github: milosgajdos83)

netlink/netlink_linux.go

@@ -189,13 +189,15 @@ func newRtAttrChild(parent *RtAttr, attrType int, data []byte) *RtAttr {
 }
 
 func (a *RtAttr) Len() int {
+	if len(a.children) == 0 {
+		return (syscall.SizeofRtAttr + len(a.Data))
+	}
+
 	l := 0
 	for _, child := range a.children {
-		l += child.Len() + syscall.SizeofRtAttr
-	}
-	if l == 0 {
-		l++
+		l += child.Len()
 	}
+	l += syscall.SizeofRtAttr
 	return rtaAlignOf(l + len(a.Data))
 }
 
@@ -203,7 +205,7 @@ func (a *RtAttr) ToWireFormat() []byte {
 	native := nativeEndian()
 
 	length := a.Len()
-	buf := make([]byte, rtaAlignOf(length+syscall.SizeofRtAttr))
+	buf := make([]byte, rtaAlignOf(length))
 
 	if a.Data != nil {
 		copy(buf[4:], a.Data)
@@ -216,11 +218,10 @@ func (a *RtAttr) ToWireFormat() []byte {
 		}
 	}
 
-	if l := uint16(rtaAlignOf(length)); l != 0 {
-		native.PutUint16(buf[0:2], l+1)
+	if l := uint16(length); l != 0 {
+		native.PutUint16(buf[0:2], l)
 	}
 	native.PutUint16(buf[2:4], a.Type)
-
 	return buf
 }
 
@@ -700,6 +701,10 @@ func nonZeroTerminated(s string) []byte {
 // Add a new network link of a specified type. This is identical to
 // running: ip add link $name type $linkType
 func NetworkLinkAdd(name string, linkType string) error {
+	if name == "" || linkType == "" {
+		return fmt.Errorf("Neither link name nor link type can be empty!")
+	}
+
 	s, err := getNetlinkSocket()
 	if err != nil {
 		return err
@@ -711,15 +716,43 @@ func NetworkLinkAdd(name string, linkType string) error {
 	msg := newIfInfomsg(syscall.AF_UNSPEC)
 	wb.AddData(msg)
 
-	if name != "" {
-		nameData := newRtAttr(syscall.IFLA_IFNAME, zeroTerminated(name))
-		wb.AddData(nameData)
+	linkInfo := newRtAttr(syscall.IFLA_LINKINFO, nil)
+	newRtAttrChild(linkInfo, IFLA_INFO_KIND, nonZeroTerminated(linkType))
+	wb.AddData(linkInfo)
+
+	nameData := newRtAttr(syscall.IFLA_IFNAME, zeroTerminated(name))
+	wb.AddData(nameData)
+
+	if err := s.Send(wb); err != nil {
+		return err
 	}
 
-	kindData := newRtAttr(IFLA_INFO_KIND, nonZeroTerminated(linkType))
+	return s.HandleAck(wb.Seq)
+}
 
-	infoData := newRtAttr(syscall.IFLA_LINKINFO, kindData.ToWireFormat())
-	wb.AddData(infoData)
+// Delete a network link. This is identical to
+// running: ip link del $name
+func NetworkLinkDel(name string) error {
+	if name == "" {
+		return fmt.Errorf("Network link name can not be empty!")
+	}
+
+	s, err := getNetlinkSocket()
+	if err != nil {
+		return err
+	}
+	defer s.Close()
+
+	iface, err := net.InterfaceByName(name)
+	if err != nil {
+		return err
+	}
+
+	wb := newNetlinkRequest(syscall.RTM_DELLINK, syscall.NLM_F_ACK)
+
+	msg := newIfInfomsg(syscall.AF_UNSPEC)
+	msg.Index = int32(iface.Index)
+	wb.AddData(msg)
 
 	if err := s.Send(wb); err != nil {
 		return err

netlink/netlink_linux_test.go

@@ -27,10 +27,35 @@ func TestCreateBridgeWithMac(t *testing.T) {
 	}
 
 	if _, err := net.InterfaceByName(name); err == nil {
-		t.Fatal("expected error getting interface because bridge was deleted")
+		t.Fatal("expected error getting interface because %s bridge was deleted", name)
 	}
 }
 
+func TestCreateBridgeLink(t *testing.T) {
+	if testing.Short() {
+		return
+	}
+
+	name := "mybrlink"
+
+	if err := NetworkLinkAdd(name, "bridge"); err != nil {
+		log.Fatal(err)
+	}
+
+	if _, err := net.InterfaceByName(name); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := NetworkLinkDel(name); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := net.InterfaceByName(name); err == nil {
+		t.Fatal("expected error getting interface because %s bridge was deleted", name)
+	}
+
+}
+
 func TestCreateVethPair(t *testing.T) {
 	if testing.Short() {
 		return

netlink/netlink_unsupported.go

@@ -19,6 +19,10 @@ func NetworkLinkAdd(name string, linkType string) error {
 	return ErrNotImplemented
 }
 
+func NetworkLinkDel(name string) error {
+	return ErrNotImplemented
+}
+
 func NetworkLinkUp(iface *net.Interface) error {
 	return ErrNotImplemented
 }