Add basic functions for dealing with network namespaces

Signed-off-by: Matthew Heon <matthew.heon@gmail.com>

Closes: #109
Approved by: mheon

libpod/networking.go

@@ -0,0 +1,65 @@
+package libpod
+
+import (
+	"github.com/containernetworking/plugins/pkg/ns"
+	"github.com/cri-o/ocicni/pkg/ocicni"
+	"github.com/sirupsen/logrus"
+)
+
+// Get an OCICNI network config
+func getPodNetwork(id, name, nsPath string, ports []ocicni.PortMappings) ocicni.PodNetwork {
+	return ocicni.PodNetwork{
+		Name:         name,
+		Namespace:    name, // TODO is there something else we should put here? We don't know about Kube namespaces
+		ID:           id,
+		NetNS:        nsPath,
+		PortMappings: ports,
+	}
+}
+
+// Create and configure a new network namespace
+func (r *Runtime) createNetNS(id, name string, ports []ocicni.PortMapping) (n ns.NetNS, err error) {
+	ns, err := ns.NewNS()
+	if err != nil {
+		return nil, errors.Wrapf(err, "error creating network namespace %s", id)
+	}
+	defer func() {
+		if err != nil {
+			if err2 := ns.Close(); err2 != nil {
+				logrus.Errorf("Error closing partially created network namespace %s: %v", id, err2)
+			}
+		}
+	}()
+
+	podNetwork := getPodNetwork(id, name, ns.Path(), ports)
+
+	if err := r.netPlugin.SetUpPod(podNetwork); err != nil {
+		return nil, errors.Wrapf(err, "error configuring network namespace %s", id)
+	}
+
+	// TODO hostport mappings for forwarded ports
+
+	return ns, nil
+}
+
+// Join an existing network namespace
+func joinNetNS(path string) (ns.NetNS, error) {
+	ns, err := ns.GetNS(path)
+	if err != nil {
+		return nil, errors.Wrapf(err, "error retrieving network namespace at %s", path)
+	}
+
+	return ns, nil
+}
+
+// Tear down a network namespace
+func (r *Runtime) teardownNetNS(id, name string, ports []ocicni.PortMapping, ns ns.NetNS) error {
+	// TODO hostport mappings for forwarded ports should be undone
+	podNetwork := getPodNetwork(id, name, ns.Path(), ports)
+
+	if err := r.netPlugin.TearDownPod(podNetwork); err != nil {
+		return errors.Wrapf(err, "failed to remove network namespace %s", id)
+	}
+
+	return nil
+}