# File lib/fog/vsphere/requests/compute/list_virtual_machines.rb, line 5
        def list_virtual_machines(options = {})
          # Listing all VM's can be quite slow and expensive.  Try and optimize
          # based on the available options we have.  These conditions are in
          # ascending order of  time to complete for large deployments.
          if options['instance_uuid'] then
            list_all_virtual_machines_by_instance_uuid(options)
          elsif options['folder'] then
            list_all_virtual_machines_in_folder(options)
          else
            list_all_virtual_machines
          end
        end