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From: MOSS@cs.umass.EDU ("Eliot Moss, GRC A351B, x5-4206")
Newsgroups: comp.os.vms
Subject: RE: Protected access to data files
Message-ID: <8708090249.AA08384@ucbvax.Berkeley.EDU>
Date: Thu, 6-Aug-87 07:16:00 EDT
Article-I.D.: ucbvax.8708090249.AA08384
Posted: Thu Aug  6 07:16:00 1987
Date-Received: Sun, 9-Aug-87 13:05:40 EDT
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Funny you should talk about using a device driver to fire up a user program
for access to files, etc. You see, years ago at an Institute not so far away
(MIT), there was (still is perhaps) an operating system called ITS for the
PDP-10 and its descendants. While definitely very much a home brew system
full of hacks (even the name ITS is a joke: Incompatible Timesharing System;
remember CTSS, the Compatible Time SHaring System?), ITS did provide a lot
of advanced features. One was the ability to run many processes at once,
organized as a tree in which each node could control its children. Another,
relevant to the case at hand, was the ability to define new devices in
software, that could do anything whatsoever (e.g., provide protected access
to files -- except ITS has no protection, so why bother, unless maybe the
active program decrypts an encrypted file, but beware! The source is
probably accessible to everyone...) Anyway, it worked by causing a job to be
fired off for each open on the device (called a JOB device, logically
enough), and the job could then open the "other side" of the device (called
the BOJ device) and extract details of each I/O request as they became
available. The OS would translate all the possible requests to a smaller
number of requests in canonial form, simplifying the BOJ device end, and
would also handle providing the data back to the client (as well as
accepting data for writes). I actually wrote one of these; it displayed a
laser printer spooler queue as I recall. Anyway, it's been done before; you
could probably get the spec to get ideas on what is necessary; and I think
it's a great idea to try to build one for VMS!

						Eliot Moss