Add plugin code

This adds basic plugins.
"main" types: veth, bridge, macvlan
"ipam" type: host-local

The code has been ported over from github.com/coreos/rkt project
and adapted to fit the CNI spec.

ip/link.go

@@ -0,0 +1,117 @@
+// Copyright 2015 CoreOS, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ip
+
+import (
+	"crypto/sha512"
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/appc/cni/Godeps/_workspace/src/github.com/vishvananda/netlink"
+)
+
+func makeVeth(name, peer string, mtu int) (netlink.Link, error) {
+	veth := &netlink.Veth{
+		LinkAttrs: netlink.LinkAttrs{
+			Name:  name,
+			Flags: net.FlagUp,
+			MTU:   mtu,
+		},
+		PeerName: peer,
+	}
+	if err := netlink.LinkAdd(veth); err != nil {
+		return nil, err
+	}
+
+	return veth, nil
+}
+
+// RandomVethName returns string "veth" with random prefix (hashed from entropy)
+func RandomVethName(entropy string) string {
+	h := sha512.New()
+	h.Write([]byte(entropy))
+	return fmt.Sprintf("veth%x", h.Sum(nil)[:5])
+}
+
+// SetupVeth sets up a virtual ethernet link.
+// Should be in container netns.
+// TODO(eyakubovich): get rid of entropy and ask kernel to pick name via pattern
+func SetupVeth(entropy, contVethName string, mtu int, hostNS *os.File) (hostVeth, contVeth netlink.Link, err error) {
+	// NetworkManager (recent versions) will ignore veth devices that start with "veth"
+	hostVethName := RandomVethName(entropy)
+	hostVeth, err = makeVeth(hostVethName, contVethName, mtu)
+	if err != nil {
+		err = fmt.Errorf("failed to make veth pair: %v", err)
+		return
+	}
+
+	if err = netlink.LinkSetUp(hostVeth); err != nil {
+		err = fmt.Errorf("failed to set %q up: %v", hostVethName, err)
+		return
+	}
+
+	contVeth, err = netlink.LinkByName(contVethName)
+	if err != nil {
+		err = fmt.Errorf("failed to lookup %q: %v", contVethName, err)
+		return
+	}
+
+	if err = netlink.LinkSetUp(contVeth); err != nil {
+		err = fmt.Errorf("failed to set %q up: %v", contVethName, err)
+		return
+	}
+
+	if err = netlink.LinkSetNsFd(hostVeth, int(hostNS.Fd())); err != nil {
+		err = fmt.Errorf("failed to move veth to host netns: %v", err)
+		return
+	}
+
+	return
+}
+
+// DelLinkByName removes an interface link.
+func DelLinkByName(ifName string) error {
+	iface, err := netlink.LinkByName(ifName)
+	if err != nil {
+		return fmt.Errorf("failed to lookup %q: %v", ifName, err)
+	}
+
+	if err = netlink.LinkDel(iface); err != nil {
+		return fmt.Errorf("failed to delete %q: %v", ifName, err)
+	}
+
+	return nil
+}
+
+// DelLinkByNameAddr remove an interface returns its IP address
+// of the specified family
+func DelLinkByNameAddr(ifName string, family int) (*net.IPNet, error) {
+	iface, err := netlink.LinkByName(ifName)
+	if err != nil {
+		return nil, fmt.Errorf("failed to lookup %q: %v", ifName, err)
+	}
+
+	addrs, err := netlink.AddrList(iface, family)
+	if err != nil || len(addrs) == 0 {
+		return nil, fmt.Errorf("failed to get IP addresses for %q: %v", ifName, err)
+	}
+
+	if err = netlink.LinkDel(iface); err != nil {
+		return nil, fmt.Errorf("failed to delete %q: %v", ifName, err)
+	}
+
+	return addrs[0].IPNet, nil
+}