Where to store the stack "state"

Hi, To add support for traffic extraction, it's necessary to introduce some nothing of "state" in the MAC layer (since the DL_USAGE must be 'remembered' to know how to interpret further data) ... Any suggestion how to achieve that as cleanly as possible ? Having a global doesn't sound that nice, but passing a struct around either. Maybe introduce a pointer to a 'tetra_state' in the primitive struct ? Cheers, Sylvain