def key_params(api):
  """Build a unique key from the builder name (as a list).

  E.g.  arch x86 gpu GeForce320M mode MacMini4.1 os Mac10.6
  """
  # Don't bother to include role, which is always Test.
  blacklist = ['role', 'test_filter']

  flat = []
  for k in sorted(api.vars.builder_cfg.keys()):
    if k not in blacklist:
      flat.append(k)
      flat.append(api.vars.builder_cfg[k])

  return flat