Fix libcontainer network support on rhel6

It seems that netlink in older kernels, including RHEL6, does not
support RTM_SETLINK with IFLA_MASTER. It just silently ignores it, reporting
no error, causing netlink.NetworkSetMaster() to not do anything yet
return no error.

We fix this by introducing and using AddToBridge() in a very similar manner
to CreateBridge(), which use the old ioctls directly.

This fixes https://github.com/dotcloud/docker/issues/4668

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)

pkg/libcontainer/network/network.go

@@ -50,7 +50,7 @@ func SetInterfaceMaster(name, master string) error {
 	if err != nil {
 		return err
 	}
-	return netlink.NetworkSetMaster(iface, masterIface)
+	return netlink.AddToBridge(iface, masterIface)
 }
 
 func SetDefaultGateway(ip string) error {

pkg/netlink/netlink_linux.go

@@ -19,6 +19,7 @@ const (
 	VETH_INFO_PEER = 1
 	IFLA_NET_NS_FD = 28
 	SIOC_BRADDBR   = 0x89a0
+	SIOC_BRADDIF   = 0x89a2
 )
 
 var nextSeqNr int
@@ -28,6 +29,11 @@ type ifreqHwaddr struct {
 	IfruHwaddr syscall.RawSockaddr
 }
 
+type ifreqIndex struct {
+	IfrnName  [16]byte
+	IfruIndex int32
+}
+
 func nativeEndian() binary.ByteOrder {
 	var x uint32 = 0x01020304
 	if *(*byte)(unsafe.Pointer(&x)) == 0x01 {
@@ -842,6 +848,30 @@ func CreateBridge(name string, setMacAddr bool) error {
 	return nil
 }
 
+// Add a slave to abridge device.  This is more backward-compatible than
+// netlink.NetworkSetMaster and works on RHEL 6.
+func AddToBridge(iface, master *net.Interface) error {
+	s, err := syscall.Socket(syscall.AF_INET6, syscall.SOCK_STREAM, syscall.IPPROTO_IP)
+	if err != nil {
+		// ipv6 issue, creating with ipv4
+		s, err = syscall.Socket(syscall.AF_INET, syscall.SOCK_STREAM, syscall.IPPROTO_IP)
+		if err != nil {
+			return err
+		}
+	}
+	defer syscall.Close(s)
+
+	ifr := ifreqIndex{}
+	copy(ifr.IfrnName[:], master.Name)
+	ifr.IfruIndex = int32(iface.Index)
+
+	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, uintptr(s), SIOC_BRADDIF, uintptr(unsafe.Pointer(&ifr))); err != 0 {
+		return err
+	}
+
+	return nil
+}
+
 func setBridgeMacAddress(s int, name string) error {
 	ifr := ifreqHwaddr{}
 	ifr.IfruHwaddr.Family = syscall.ARPHRD_ETHER

pkg/netlink/netlink_unsupported.go

@@ -63,3 +63,7 @@ func NetworkLinkDown(iface *net.Interface) error {
 func CreateBridge(name string, setMacAddr bool) error {
 	return ErrNotImplemented
 }
+
+func AddToBridge(iface, master *net.Interface) error {
+	return ErrNotImplemented
+}