fd type from number

[loris@draios.com (Loris Degioanni)]

(resending making sure this is not part of another thread)

I'm looking for an efficient way to determine the type of an fd (file, 
socket...) given its number, from a kernel module.
The closest thing I found by looking at the kernel sources is 
sockfd_lookup(), which works but is limited to telling me if the fd is a 
socket or not.

Is there something else I can look at?

Thank you in advance,
Loris