look_up_user_keyrings
extern int look_up_user_keyrings(struct key **, struct key **);
ret = look_up_user_keyrings(NULL, &user_session);
ret = look_up_user_keyrings(&key, NULL);
ret = look_up_user_keyrings(NULL, &key);
return look_up_user_keyrings(NULL, NULL);
ret = look_up_user_keyrings(NULL, &user_session);
ret = look_up_user_keyrings(NULL, &dest_keyring);
ret = look_up_user_keyrings(&dest_keyring, NULL);