keyring_restrict
rc = keyring_restrict(make_key_ref(keyring, true), NULL, NULL);
keyring_restrict(make_key_ref(dm_verity_keyring, true), NULL, NULL))
extern int keyring_restrict(key_ref_t keyring, const char *type,
ret = keyring_restrict(key_ref, _type ? type : NULL, restriction);
EXPORT_SYMBOL(keyring_restrict);