Add error message for ifname collision (#74)

* Add error message for ifname collision

This changes introduce to validateIfName, to check the validation
for interface name, i.e. same name among two or more interfaces.

vendor/github.com/vishvananda/netns/netns_test.go

@@ -0,0 +1,66 @@
+package netns
+
+import (
+	"runtime"
+	"sync"
+	"testing"
+)
+
+func TestGetNewSetDelete(t *testing.T) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	origns, err := Get()
+	if err != nil {
+		t.Fatal(err)
+	}
+	newns, err := New()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if origns.Equal(newns) {
+		t.Fatal("New ns failed")
+	}
+	if err := Set(origns); err != nil {
+		t.Fatal(err)
+	}
+	newns.Close()
+	if newns.IsOpen() {
+		t.Fatal("newns still open after close", newns)
+	}
+	ns, err := Get()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ns.Equal(origns) {
+		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)
+	}
+}
+
+func TestThreaded(t *testing.T) {
+	ncpu := runtime.GOMAXPROCS(-1)
+	if ncpu < 2 {
+		t.Skip("-cpu=2 or larger required")
+	}
+
+	// Lock this thread simply to ensure other threads get used.
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	wg := &sync.WaitGroup{}
+	for i := 0; i < ncpu; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			TestGetNewSetDelete(t)
+		}()
+	}
+	wg.Wait()
+}