🚀 go-pugleaf

After reading up on cross-memory services (Extended Addressability Guide and the James Antognini
article), I have the following questions:

1.  Assuming I want to connect only selected address spaces to the service address space (via
non-system LX):

              a.  to execute the ATSET and ETCON macros in the user's address space (assuming the
user runs in problem
                   state) I will have to create an additional  PC routine to check authorization and
issue those macros on behalf of
                   the user.

              b. that additional PC routine will have to be based on a system LX, otherwise I will
enter a logical endless loop
                  (<g>)

              c. in other words: I will need to reserve two LX's - one system, one non-system

My question is: is this worth it? Is this the customary way of doing things?  Or for economy's sake
do people end up using  a single system LX even for connection to selected address spaces (unless
those selected address spaces are in supervisor mode)?

2.  When I getmain a global area in common storage to save the cross-memory info (PC numbers,
(dormant) system LX, etc.), in what key should I getmain it?   What are the "safe" keys that people
are accustomed to using?  (I gather from earlier discussions on this list that key 8 is a no-no.)

3. The notion and purpose of an "EAX" (as opposed to a simple "AX") is not clearly elucidated in
either of the above papers
-- both more or less assume one already pretty much knows what it is and give it short shrift.  Can
anyone point me to a more precise presentation of the EAX, or, alternatively,  briefly explain in
this forum when and for what reason one would opt to reserve an EAX and specify it in the ETDEF
macro?

I am sure I will have some more questions but that's enough for now!

Thanks,
John Krew

p.s. also cross-posted to IBM-MAIN