code: func (mp *MachineProvider) poll(ctx context.Context, hostname, backend string) (*machine.ComponentsMachineProviderRpcMessagesPollResponse, error) {
  	return mp.client.Poll(&machine.ComponentsMachineProviderRpcMessagesPollRequest{
  		Backend:  backend,
  		Hostname: hostname,
  	}).Context(ctx).Do()
  }
docs: // poll polls Machine Provider for instructions.
  //
  // Returns an Instruction.