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From: terryl@tekcrl.TEK.COM
Newsgroups: comp.unix.xenix,comp.sources.wanted,comp.unix.questions
Subject: Re: tty watcher
Message-ID: <1951@tekcrl.TEK.COM>
Date: Thu, 17-Sep-87 18:16:22 EDT
Article-I.D.: tekcrl.1951
Posted: Thu Sep 17 18:16:22 1987
Date-Received: Sun, 20-Sep-87 11:48:36 EDT
References: <1180@mtune.ATT.COM> <198@flmis06.ATT.COM>
Reply-To: terryl@tekcrl.tek.com
Organization: Tektronix, Inc., Beaverton, OR.
Lines: 33
Xref: mnetor comp.unix.xenix:778 comp.sources.wanted:2311 comp.unix.questions:4166

In article <198@flmis06.ATT.COM> mikel@flmis06.ATT.COM (Mikel Manitius) writes:
>>2) is the major point here; there are no tty watchers that consist solely of a
>>user-mode program that drops on top of a non-hacked UNIX system.
>
>I saw this done on 4.1bsd once, I even had the code that did it. It was
>a simple program that figured out where the clist struct was for that user's
>tty driver, and scanned it repeatidly in /dev/kmem for changes. It would
>output his input line by line.
>
>This sort of thing should be feasable on most Unix systems... It's just
>a pain figuring out where to find his clist, especially given just a
>tty name.

     Actually, if you have a tty name, it is quite trivial to figure out
where the C-list structure lives in kernel memory (assuming you have at
least read access to /dev/kmem).

	****WARNING, WILL ROBINSON!!! SPOILER AHEAD!!!****

     It goes like this: first, do a stat(2) on said tty name. Inside of
the stat structure returned is a field giving the major/minor number of
the tty. Take the major number and use this to index into the cdevsw[]
structure. One of the fields in the cdevsw[] structure is a pointer to
the FIRST tty structure for the specific RS-232 device. Now use the minor
number gotten from the stat(2) call to index into the tty structure. You
now have a pointer to the tty structure for the tty name in question. It
is left as an exercise to the student to find the appropriate C-list struc-
ture.


				Terry Laskodi
				     of
				Tektronix