Add method for empty ns handle

netns_linux.go

@@ -60,6 +60,9 @@ func (ns NsHandle) Equal(other NsHandle) bool {
 // String shows the file descriptor number and its dev and inode.
 func (ns NsHandle) String() string {
 	var s syscall.Stat_t
+	if ns == -1 {
+		return "NS(None)"
+	}
 	if err := syscall.Fstat(int(ns), &s); err != nil {
 		return fmt.Sprintf("NS(%d: unknown)", ns)
 	}
@@ -81,6 +84,11 @@ func (ns *NsHandle) Close() error {
 	return nil
 }
 
+// Get an empty (closed) NsHandle
+func None() NsHandle {
+	return NsHandle(-1)
+}
+
 // Set sets the current network namespace to the namespace represented
 // by NsHandle.
 func Set(ns NsHandle) (err error) {

netns_test.go

@@ -35,3 +35,10 @@ func TestGetNewSetDelete(t *testing.T) {
 		t.Fatal("Reset ns failed", origns, newns, ns)
 	}
 }
+
+func TestNone(t *testing.T) {
+	ns := None()
+	if ns.IsOpen() {
+		t.Fatal("None ns is open", ns)
+	}
+}