func()

in pkg/netnswrapper/netns_linux.go [42:109]
43 lines of code
8 McCabe index (conditional complexity)

func (*netns) NewNS(nsName string) (ns.NetNS, error) {
	// Create the directory for mounting network namespaces
	// This needs to be a shared mountpoint in case it is mounted in to
	// other namespaces (containers)
	err := os.MkdirAll(nsBaseDir, 0755)
	if err != nil {
		return nil, err
	}

	// create an empty file at the mount point and fail if it already exists
	nsPath := path.Join(nsBaseDir, nsName)
	mountPointFd, err := os.OpenFile(nsPath, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
	if err != nil {
		return nil, err
	}
	mountPointFd.Close()

	// Ensure the mount point is cleaned up on errors
	defer func() {
		if err != nil {
			os.RemoveAll(nsPath)
		}
	}()

	var wg sync.WaitGroup
	wg.Add(1)

	// do namespace work in a dedicated goroutine, so that we can safely
	// Lock/Unlock OSThread without upsetting the lock/unlock state of
	// the caller of this function
	go (func() {
		defer wg.Done()
		runtime.LockOSThread()
		// Don't unlock. By not unlocking, golang will kill the OS thread when the
		// goroutine is done (for go1.10+)

		var origNS ns.NetNS
		origNS, err = ns.GetNS(getCurrentThreadNetNSPath())
		if err != nil {
			return
		}
		defer origNS.Close()

		// create a new netns on the current thread
		err = unix.Unshare(unix.CLONE_NEWNET)
		if err != nil {
			return
		}

		// Put this thread back to the orig ns, since it might get reused (pre go1.10)
		defer func() { _ = origNS.Set() }()

		// bind mount the netns from the current thread (from /proc) onto the
		// mount point. This causes the namespace to persist, even when there
		// are no threads in the ns.
		err = unix.Mount(getCurrentThreadNetNSPath(), nsPath, "none", unix.MS_BIND, "")
		if err != nil {
			err = fmt.Errorf("failed to bind mount ns at %s: %v", nsPath, err)
		}
	})()
	wg.Wait()

	if err != nil {
		return nil, fmt.Errorf("failed to create namespace: %v", err)
	}

	return ns.GetNS(nsPath)
}