calculating an aspect of shared buffer state from a background worker

Dear Hackers --

I'm looking at doing a calculation to determine the number of free buffers
available. A n example ratio that is based on some data structures in
freelist.c as follows:

(StrategyControl->lastFreeBuffer - StrategyControl->firstFreeBuffer) /
(double) NBuffers

Is there a way to get access to the StrategyControl pointer in the context
of a background worker?

Thanks,
Robert