Checkpassword and FD3 - the problem

The problem:

Systems which use uthread as the threading implementation take up file
descriptors 3 and 4 with a pipe apparently used to do signalling between
threads?

I don't really know what it's for - I just know that my python program
(python uses pthreads and thus uthread) cannot close or dup2 FD3, so that it
is very difficult to use checkpassword directly.

I have the obvious kludge solutions like calling "/bin/sh -c 'python
3</dev/null'", calling python from a C wrapper which opens a file first, or
calling "/bin/sh -c 'checkpassword 3<&0'" from within python, but these are
not very nice.

I'm very curious:

Why is the checkpassword interface so married to FD#3?  Why not stdin?

Why can't I set the env variable "CHECKPASSWORDFD=125" and have it use that
instead, or have some other configurable mechanism to force a different FD?

If there's a FAQ about this somewhere, please direct me to it!

--
Jim Ramsay
[email protected]