Merge pull request #3 from deepakkumarbhagat/link_modify

Link modify, re-base from upstream

link_linux.go

@@ -1012,18 +1012,12 @@ func (h *Handle) LinkAdd(link Link) error {
 	return h.linkModify(link, unix.NLM_F_CREATE|unix.NLM_F_EXCL|unix.NLM_F_ACK)
 }
 
-// LinkModify modify an existing link device. The type and features of the device
-// are taken from the parameters in the link object.
-// Equivalent to: `ip link add $link`
 func LinkModify(link Link) error {
 	return pkgHandle.LinkModify(link)
 }
 
-// LinkModify modify an existing link device. The type and features of the device
-// are taken from the parameters in the link object.
-// Equivalent to: `ip link add $link`
 func (h *Handle) LinkModify(link Link) error {
-	return h.linkModify(link, unix.NLM_F_CREATE|unix.NLM_F_ACK)
+	return h.linkModify(link, unix.NLM_F_REQUEST|unix.NLM_F_ACK)
 }
 
 func (h *Handle) linkModify(link Link, flags int) error {
@@ -1171,6 +1165,11 @@ func (h *Handle) linkModify(link Link, flags int) error {
 	nameData := nl.NewRtAttr(unix.IFLA_IFNAME, nl.ZeroTerminated(base.Name))
 	req.AddData(nameData)
 
+	if base.Alias != "" {
+		alias := nl.NewRtAttr(unix.IFLA_IFALIAS, []byte(base.Alias))
+		req.AddData(alias)
+	}
+
 	if base.MTU > 0 {
 		mtu := nl.NewRtAttr(unix.IFLA_MTU, nl.Uint32Attr(uint32(base.MTU)))
 		req.AddData(mtu)

link_test.go

@@ -492,6 +492,37 @@ func TestLinkAddDelDummyWithGroup(t *testing.T) {
 	testLinkAddDel(t, &Dummy{LinkAttrs{Name: "foo", Group: 42}})
 }
 
+func TestLinkModify(t *testing.T) {
+	tearDown := setUpNetlinkTest(t)
+	defer tearDown()
+
+	linkName := "foo"
+	originalMTU := 1500
+	updatedMTU := 1442
+
+	link := &Dummy{LinkAttrs{Name: linkName, MTU: originalMTU}}
+	base := link.Attrs()
+
+	if err := LinkAdd(link); err != nil {
+		t.Fatal(err)
+	}
+
+	link.MTU = updatedMTU
+	if err := LinkModify(link); err != nil {
+		t.Fatal(err)
+	}
+
+	result, err := LinkByName(linkName)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rBase := result.Attrs()
+	if rBase.MTU != updatedMTU {
+		t.Fatalf("MTU is %d, should be %d", rBase.MTU, base.MTU)
+	}
+}
+
 func TestLinkAddDelIfb(t *testing.T) {
 	tearDown := setUpNetlinkTest(t)
 	defer tearDown()