necessity for "extern" in function prototype?

["Min-Hua Chen" <orca.chen@xxxxxxxxx>]

Hi:

I note that the headers of the linux source have "extern" in the function protoptye.
I think the extern is not necessary because all function in C are global (except static functions),
on the other hand, adding "extern" in prototype makes the code easy to read.

Is there any stronger reason for adding "extern" in function prototype?

regards,
Min-Hua