How to get the file descriptor of a handle?

Hello I'd like to know how you get the file descriptor, which is incapsulated in a handle. The libraries GHC.IO.Handle/GHC.IO.Handle.FD only provide for the other direction. The function haFD, which I've used before I've updated to the current version of GHC (6.12), appears to be in use two times in the libraries. But there isn't a definition anywhere. Any help would be appreciated. Cheers, Volker -- Volker Wysk