Add support for getting links in different namespaces

link_linux.go

@@ -2113,6 +2113,60 @@ func (h *Handle) LinkByIndex(index int) (Link, error) {
 	return execGetLink(req)
 }
 
+// LinkByIndexAndNsid finds a link by index in a different namespace and returns a pointer to the object
+func LinkByIndexAndNsid(index int, nsid int) (Link, error) {
+	return pkgHandle.LinkByIndexAndNsid(index, nsid)
+}
+
+// LinkByIndexAndNsid finds a link by index in a different namespace and returns a pointer to the object
+func (h *Handle) LinkByIndexAndNsid(index int, nsid int) (Link, error) {
+	req := h.newNetlinkRequest(unix.RTM_GETLINK, unix.NLM_F_ACK)
+
+	msg := nl.NewIfInfomsg(unix.AF_UNSPEC)
+	msg.Index = int32(index)
+	req.AddData(msg)
+
+	attr := nl.NewRtAttr(unix.IFLA_TARGET_NETNSID, nl.Uint32Attr(uint32(nsid)))
+	req.AddData(attr)
+
+	if h.options.collectVFInfo {
+		attr := nl.NewRtAttr(unix.IFLA_EXT_MASK, nl.Uint32Attr(nl.RTEXT_FILTER_VF))
+		req.AddData(attr)
+	}
+
+	return execGetLink(req)
+}
+
+// LinkByNameAndNsid finds a link by name in a different namespace and returns a pointer to the object
+func LinkByNameAndNsid(name string, nsid int) (Link, error) {
+	return pkgHandle.LinkByNameAndNsid(name, nsid)
+}
+
+// LinkByNameAndNsid finds a link by name in a different namespace and returns a pointer to the object
+func (h *Handle) LinkByNameAndNsid(name string, nsid int) (Link, error) {
+	req := h.newNetlinkRequest(unix.RTM_GETLINK, unix.NLM_F_ACK)
+
+	msg := nl.NewIfInfomsg(unix.AF_UNSPEC)
+	req.AddData(msg)
+
+	attr := nl.NewRtAttr(unix.IFLA_TARGET_NETNSID, nl.Uint32Attr(uint32(nsid)))
+	req.AddData(attr)
+
+	if h.options.collectVFInfo {
+		attr := nl.NewRtAttr(unix.IFLA_EXT_MASK, nl.Uint32Attr(nl.RTEXT_FILTER_VF))
+		req.AddData(attr)
+	}
+
+	nameData := nl.NewRtAttr(unix.IFLA_IFNAME, nl.ZeroTerminated(name))
+	if len(name) > 15 {
+		nameData = nl.NewRtAttr(unix.IFLA_ALT_IFNAME, nl.ZeroTerminated(name))
+	}
+	req.AddData(nameData)
+
+	link, err := execGetLink(req)
+	return link, err
+}
+
 func execGetLink(req *nl.NetlinkRequest) (Link, error) {
 	msgs, err := req.Execute(unix.NETLINK_ROUTE, 0)
 	if err != nil {

link_test.go

@@ -2220,6 +2220,38 @@ func TestLinkByIndex(t *testing.T) {
 	}
 }
 
+func TestLinkByIndexAndNsid(t *testing.T) {
+	minKernelRequired(t, 4, 15)
+	t.Cleanup(setUpNetlinkTest(t))
+	nsId, linkIdx, linkName, cleanup := setUpNamespaceWithLink(t)
+	t.Cleanup(cleanup)
+
+	link, err := LinkByIndexAndNsid(linkIdx, nsId)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if link.Attrs().Name != linkName {
+		t.Fatal("did not get the correct link")
+	}
+}
+
+func TestLinkByNameAndNsid(t *testing.T) {
+	minKernelRequired(t, 4, 15)
+	t.Cleanup(setUpNetlinkTest(t))
+	nsId, linkIdx, linkName, cleanup := setUpNamespaceWithLink(t)
+	t.Cleanup(cleanup)
+
+	link, err := LinkByNameAndNsid(linkName, nsId)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if link.Attrs().Index != linkIdx {
+		t.Fatal("did not get the correct link")
+	}
+}
+
 func TestLinkSet(t *testing.T) {
 	t.Cleanup(setUpNetlinkTest(t))
 

netlink_test.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"crypto/rand"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"log"
@@ -264,6 +265,82 @@ func setUpNamedNetlinkTestWithKModule(t *testing.T, moduleNames ...string) (stri
 	return setUpNamedNetlinkTest(t)
 }
 
+func setUpNamespaceWithLink(t *testing.T) (nsId int, linkId int, linkName string, teardown tearDownNetlinkTest) {
+	skipUnlessRoot(t)
+	nsName, cleanupNs := setUpNamedNetlinkTest(t)
+
+	ok := false
+	defer func() {
+		if !ok {
+			cleanupNs()
+		}
+	}()
+
+	cmd := exec.Command("ip", "netns", "set", nsName, "auto")
+	var stderr bytes.Buffer
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		if strings.Contains(stderr.String(), "Invalid") {
+			t.Skip("iproute2 version is too old")
+		}
+
+		t.Fatalf("Failed to run: ip netns set %s auto", nsName)
+	}
+
+	// create a random name
+	rnd := make([]byte, 4)
+	if _, err := rand.Read(rnd); err != nil {
+		t.Fatal("failed creating random link name")
+	}
+	name := hex.EncodeToString(rnd)
+
+	if err := exec.Command("ip", "netns", "exec", nsName, "ip", "link", "add", name, "type", "dummy").Run(); err != nil {
+		t.Fatalf("Failed to run: ip netns exec %s ip link add %s type dummy", nsName, name)
+	}
+
+	cmd = exec.Command("ip", "netns", "exec", nsName, "ip", "--json", "link", "show", name)
+	var stdout bytes.Buffer
+	stderr.Reset()
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+	if err := cmd.Run(); err != nil {
+		if strings.Contains(stderr.String(), "unknown") {
+			t.Skip("iproute2 version is too old")
+		}
+
+		t.Fatalf("Failed to run: %s", cmd)
+	}
+
+	var ipOutput []struct {
+		Index int `json:"ifindex"`
+	}
+
+	err := json.Unmarshal(stdout.Bytes(), &ipOutput)
+	if err != nil {
+		t.Fatalf("Failed to parse json")
+	}
+
+	if len(ipOutput) != 1 {
+		t.Fatalf("failed to get created link")
+	}
+
+	ns, err := netns.GetFromName(nsName)
+	if err != nil {
+		t.Fatalf("getting ns: %v", err)
+	}
+
+	defer ns.Close()
+
+	nsid, err := GetNetNsIdByFd(int(ns))
+	if err != nil {
+		t.Fatalf("getting nsid: %v", err)
+	}
+
+	ok = true
+
+	return nsid, ipOutput[0].Index, name, cleanupNs
+}
+
 func remountSysfs() error {
 	if err := unix.Mount("", "/", "none", unix.MS_SLAVE|unix.MS_REC, ""); err != nil {
 		return err