jsavoye wrote:Looking at this again, I see that the EXLST of X'85' just says that it is the last exit. But the manual also says that the EXLST is invoked on each OPEN macro I issue. In this case, I am not issuing an open for the unlike file, although perhaps the system is doing so internally and it is essentially as if I did.
Yes, you are, effectively, doing an OPEN, so your DCB exit routine will be entered.
The X'80' in X'85' says this entry in the address list that DCBEXLST points to is the last entry in the address list. There is no concept of a "last exit."
I think - though I'm not certain about this - that you can do what you want to do, but you have to signal your mainline code to switch from logic to process RECFM=F data to process RECFM=V data. Read the topics "Concatenating Unlike Data Sets" and "Calls to DCB OPEN Exit for Sequential Concatenation" in DFSMS Using Data Sets
for your z/OS release very carefully.