Hey Eric:
You might want to start your exploration at a higher level than the
lowest level you can possibly go to understand the internals of z/OS
I/O. For example you might want to look at EXCP or EXCPVR first, as both
prepare for entry into IOS, but both do special setup functions to make
that possible.
As an example of the setup needed, consider the difference between EXCP
and EXCPVR. EXCP, among other preliminary things, converts all addresses
in the channel program CCWs being passed to IOS from virtual to real
addresses. Ultimately, these areas must be pagefixed so as to remain in
storage during the actual I/O operation. Since STARTIO comes at the next
lower level, everything that an access method must do before calling
EXCP must also be done. This includes creating a DCB, an IOSB, etc.
I would recommend you start here, if you haven't already. as it covers
EXCP and EXCPVR.
https://www.ibm.com/support/knowledgecenter/SSLTBW_2.1.0/com.ibm.zos.v2r1.idas300/eyocp.htm
Mike Myers
On 2/8/20 12:48 PM, Erik Janssen wrote:
Hello List,
Out of curiosity I want to learn a bit more about startio. Don't worry, I won't go and
attempt to mess up someones z/os lpar, it is just for pure nerd brain entertainment.
Searching through the archives I found that there is a whitepaper that was written by
Peter Haas called "The STARTIO Facility of MVS", that there were some examples
called startio.txt or startio.ex.txt, that Bill Fairchild gave a SHARE presentation on
the subject in March 2009 in Austin and that IBM documented it, partially, in IOS logic
manuals; the versions for
OS/VS2 R2 through R3.8 were publicly available.
My search engines efforts to find any of the mentioned documents have failed so
far, so is there anybody on the list that has (some of) the mentioned documents
available and is willing to share?
Kind regards,
Erik Janssen.
PS. I had posted the same question through Google groups, but that doesn't work
in a way that the actual list gets the message it seems.
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