util: Libify socketset

Add the ReceiveBytes, ReceiveNetlinkMessage, and ReceiveUEvent methods.
This is because not everything passed through a netlink socket cannot
reliably be parsed using the ParseNetLinkMessage function.

With the ReceiveUEvent method, we add support for "uevent" kernel
events, which updates us about the state of devices currently on the
system. To make using this method easier, we add a UEvent struct, that
has the action (what event), Devpath (where the device lives in /proc or
/sysfs), and Subsystem (what subsystem this event belows to).

engine/resources/net.go

@@ -42,6 +42,7 @@ import (
 	// do not clean up spawned goroutines. Should be replaced when a suitable
 	// alternative is available.
 	"github.com/vishvananda/netlink"
+	"golang.org/x/sys/unix"
 )
 
 func init() {
@@ -195,7 +196,7 @@ func (obj *NetRes) Watch() error {
 	defer wg.Wait()
 
 	// create a netlink socket for receiving network interface events
-	conn, err := socketset.NewSocketSet(rtmGrps, obj.socketFile)
+	conn, err := socketset.NewSocketSet(rtmGrps, obj.socketFile, unix.NETLINK_ROUTE)
 	if err != nil {
 		return errwrap.Wrapf(err, "error creating socket set")
 	}
@@ -223,7 +224,7 @@ func (obj *NetRes) Watch() error {
 		defer close(nlChan)
 		for {
 			// receive messages from the socket set
-			msgs, err := conn.Receive()
+			msgs, err := conn.ReceiveNetlinkMessages()
 			if err != nil {
 				select {
 				case nlChan <- &nlChanStruct{