> Hmm. I take that back. I don't think any of this really belongs in Objects/longobject.c.
I am also not happy with that. Originally they were in Modules/posixmodule.c. However where should we place the declarations? We have not posixmodule.h. PyLong_FromPid()/PyLong_AsPid() placed right in Include/longobject.h. Are you have any suggestions?
> Is it possible to just use PyLong_FromLong / PyLong_FromLongLong etc. depending on the precision of uid_t / gid_t?
No. uid_t/gid_t can be large than maximal signed long, and long long can be not defined. See issue2005 where more complex patch proposed.