Is there any reason retrieve IP every time in Hyper-V?

[lingsamuel]

Inside Start, we already set IPAddress

machine/drivers/hyperv/hyperv.go

Lines 362 to 372 in 4f91040

	func (d *Driver) Start() error {
	if err := cmd("Hyper-V\\Start-VM", d.MachineName); err != nil {
	return err
	}
	ip, err := d.waitForIP()
	if err != nil {
	return err
	}
	d.IPAddress = ip

But inside GetIP, we retrieve IP instead of use cached value.

machine/drivers/hyperv/hyperv.go

Lines 433 to 453 in 4f91040

	func (d *Driver) GetIP() (string, error) {
	s, err := d.GetState()
	if err != nil {
	return "", err
	}
	if s != state.Running {
	return "", drivers.ErrHostIsNotRunning
	}
	stdout, err := cmdOut("((", "Hyper-V\\Get-VM", d.MachineName, ").networkadapters[0]).ipaddresses[0]")
	if err != nil {
	return "", err
	}
	resp := parseLines(stdout)
	if len(resp) < 1 {
	return "", fmt.Errorf("IP not found")
	}
	return resp[0], nil
	}

[lingsamuel]

By this simple patch, we could reduce a huge latency (each cmdOut takes about 1s).

[afbjorklund]

I think it got changed along the way: fa8fa69

Before, it would allow running with DHCP (just like in the VirtualBox driver)

Can you open a PR in docker/machine as well, just for showing good will ?

Given implementation, your optimization sounds doable.

[lingsamuel]

Opened docker#4870