'White list constructor
For example, followed json string specifies that devices whose
vendor_id is \'8086\' and product_id is \'1520\' can be assigned
to guest.
\'[{"product_id":"1520", "vendor_id":"8086"}]\'
:param whitelist_spec: A json string for a list of dictionaries,
each dictionary specifies the pci device
properties requirement.'

def __init__(self, whitelist_spec=None):

    super(Whitelist, self).__init__()
    if whitelist_spec:
        self.specs = self._parse_white_list_from_config(whitelist_spec)
    else:
        self.specs = []
