MySQL -- finding whether there's a transaction started

Hello list, I'm developing a library and would need to know if the code calling my library has already started a MySQL transaction or not. I want to know whether I should start one or use savepoints instead -- starting a transaction if one is already in progress commits the existing transaction, and setting a savepoint silently fails outside transactions. And I was unable to find any non-destructive way of retrieving that information -- is there any? Thank you, Bogdan