Would it not be a good idea to have some kind of macro defined when
tcp_window_tracking in built into netfilter so that all of the helpers
and other code that are doing things like TCP checksum verification
and whatnot, can avoid wasting cycles doing it a second time?

Then helpers could wrap their tcp checksum calls with something like:

#ifndef TCP_WINDOW_TRACKING
...
#endif

Or is a runtime check a better idea?  If so what test could be done at
runtime to know that tcp_window_tracking is checking TCP checksums?

b.

-- 
Brian J. Murrell