Thank you Maxim, your suggestion will definitely work for me.

Are you familiar with any simple "non-core" module that does it ? I will need to test for the existence of this function or the need to explicitly add librt, and update CORE_LIBS accordingly + define some preprocessor macro that I can later #ifdef on in my code.

I googled this up:
https://github.com/bigplum/nginx-tcp-lua-module/blob/master/config
but don't really understand what is going on there :)

Thanks,

Eran