Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!gatech!bbn!diamond.bbn.com!aweinste
From: aweinste@bbn.com (Anders Weinstein)
Newsgroups: comp.unix.wizards,comp.bugs.4bsd
Subject: tty selects for input in background processes
Message-ID: <7510@diamond.BBN.COM>
Date: Tue, 28-Jul-87 18:57:31 EDT
Article-I.D.: diamond.7510
Posted: Tue Jul 28 18:57:31 1987
Date-Received: Thu, 30-Jul-87 03:37:21 EDT
Reply-To: aweinste@bbn.com (Anders Weinstein)
Distribution: world
Organization: BBN Laboratories Incorporated, Cambridge, MA
Lines: 17
Xref: mnetor comp.unix.wizards:3462 comp.bugs.4bsd:467

In both 4.2 & 4.3, a select on a tty will return with input ready *even if*
the selecting process is in the background and can't actually read the typed
line or character.  The FIONREAD ioctl has the same defect.  I place the bug
in the "ttnread" routine, which is missing the appropriate check on the
process groups.

This has stymied my attempt to write a user-ftp-like program which must
multiplex handling tty commands with network input (and is very likely to be
kept in the background while idle). I know I can avoid blocking on the
background read attempts, but I don't want the idle process to wake up every
time the user types a line in the foreground.  I'm considering spawning
another process (/bin/cat comes to mind) just to funnel me the tty input
through a pipe -- this all just so I can do a select on it. Any alternative
suggestions would be welcome.

Anders Weinstein
BBN Labs