RE: File Read -- MI400

Since I asked the original question, how does one go about requesting
such a thing from IBM?

-----Original Message-----
From: bvining@vnet.ibm.com [mailto:bvining@vnet.ibm.com]
Sent: Wednesday, February 16, 2000 11:14 PM
To: MI400@midrange.com
Subject: File Read


Be aware though that you are starting down a potentially long road.

Some of the things to keep in mind (and not necessarily an exhaustive
list as these are just off the top):

1. The parameters passed to the various QDB* programs are not 
documented.
   One might be able to figure out how a particular language compiler
   interfaces with a given QDB* program; but that is hardly the same as
   knowing all options and features.  As ALL system calls to these
   programs would be going through your code you may find "interesting"
   side effects/values.  Such a wrapper would not be supported by IBM.

2. Modification of the SEPT in order to create your own exit is not
   supported by IBM, and can require additional work at higher security
   levels.  This is an area where breakage of your application can
   occur (and has in the past).

3. Some interfaces which allow the reading of files do not go through
   the QDB* programs.  Some that readily come to mind are the various
   Database MI instructions.  These instructions are blocked, but that
   doesn't necessarily equate to not used.  The wrapper approach
   therefore is not a complete solution.  And as IBM use (or non-use)
   of the QDB* programs is an implementation detail always subject to
   change you are unlikely to find any IBM supported documentation
   of which parts of the system you may catch with a wrapper, and which
   parts you won't catch.

I would urge you to ask IBM for a system provided interface to
this type of information.  Whether any solution would be based on an
exit point, a read trigger, or something else could be decided at some
future point (if sufficient requests are made); but at least it would
be an IBM supported approach that you could reliably use in the running
of your system.  The proposed approach of modifying the SEPT will
leave you outside of normal support.

Bruce Vining

>
>...     I think the idea of wrapping the existing program is excellent.
>It'd be like an exit program, only with no existing exit point.  ...
>

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