ipvlan: support enslaving an interface returned by ipam

For IP allocation schemes that cannot be interface agnostic, master can be set
to "ipam". In this configuration, the IPAM plugin is required to return a single
interface name for the ipvlan plugin to enslave.

plugins/main/ipvlan/ipvlan_test.go

@@ -224,4 +224,40 @@ var _ = Describe("ipvlan Operations", func() {
 		})
 		Expect(err).NotTo(HaveOccurred())
 	})
+
+	It("errors if master should originate from ipam but an ipam interface is not returned", func() {
+		const IFNAME = "ipvl0"
+
+		conf := `{
+    "cniVersion": "0.3.1",
+    "name": "mynet",
+    "type": "ipvlan",
+    "master": "ipam",
+    "ipam": {
+        "type": "host-local",
+        "subnet": "10.1.2.0/24"
+    }
+}`
+		targetNs, err := ns.NewNS()
+		Expect(err).NotTo(HaveOccurred())
+		defer targetNs.Close()
+
+		args := &skel.CmdArgs{
+			ContainerID: "dummy",
+			Netns:       targetNs.Path(),
+			IfName:      IFNAME,
+			StdinData:   []byte(conf),
+		}
+
+		err = originalNS.Do(func(ns.NetNS) error {
+			defer GinkgoRecover()
+
+			_, _, err := testutils.CmdAddWithResult(targetNs.Path(), IFNAME, []byte(conf), func() error {
+				return cmdAdd(args)
+			})
+			Expect(err.Error()).To(Equal("IPAM plugin returned missing master interface"))
+			return nil
+		})
+		Expect(err).NotTo(HaveOccurred())
+	})
 })