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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: hacknews
Subject: getty(8) made more resistant to line noise
Message-ID: <4309@utzoo.UUCP>
Date: Wed, 12-Sep-84 17:59:00 EDT
Article-I.D.: utzoo.4309
Posted: Wed Sep 12 17:59:00 1984
Date-Received: Wed, 12-Sep-84 17:59:00 EDT
Organization: U of Toronto Zoology
Lines: 26

Getty(8) has been modified to prevent the well-known phenomenon in
which the wtmp file bloats ridiculously in the presence of a noisy
line.  As near as we can figure it out, this problem is caused like
this:

	1. Getty is basically throwing away characters with framing
		errors, which is why getty piles up cpu time in the
		presence of line noise.
	2. When getty gets 16 characters or so without framing errors,
		it thinks it's got a login name.  (The next-char loop
		terminates on array overflow as well as on an explicit
		newline.)  So it gets things set up to invoke login.
	3. Among other setup chores, it sets the tty into cooked mode.
		Framing errors are now taken as interrupts.
	4. A framing error destroys the getty, causing init to write
		a logoff record and fork a new getty.

Two changes have been made to getty.  First, array overflow no longer
terminates the get-login-name loop; it just recycles the array pointer
back to the beginning of the array.  Second, getty sets SIGINT to
"ignored" before flipping the tty into cooked mode.  (This doesn't hurt
login(1), since login does the same thing with SIGINT immediately on
invocation.)
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry