Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site oliveb.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!crsp!pesnta!hplabs!oliveb!jerry From: jerry@oliveb.UUCP (Jerry Aguirre) Newsgroups: net.unix-wizards,net.dcom Subject: Re: any harm in allowing only ctrl-Q to restart output? Message-ID: <252@oliveb.UUCP> Date: Fri, 18-Jan-85 20:22:08 EST Article-I.D.: oliveb.252 Posted: Fri Jan 18 20:22:08 1985 Date-Received: Sun, 20-Jan-85 08:01:10 EST References: <247@lsuc.UUCP> Organization: Olivetti ATC, Cupertino, Ca Lines: 36 Xref: watmath net.unix-wizards:11621 net.dcom:808 I have made a modification to our system to do this. We run mostly vt100s and the interference of type ahead with the vt100's Xon/Xoff can be annoying. The problem can occur when the user types during high baud rate output. For example cat a large file and while it is outputing type in the next command. The screen will contain blocks which are the vt100's way of telling you that it's input buffer overflowed. It can be hard to duplicate this as system load may slow the output and some vt100s have larger input buffers than others. It is easy to exaggerate the problem though. Just cat a large file, quickly type control-S, type a space, wait a few seconds, then type control-Q. The resulting output will be truncated because Unix restarted the output after the space and the vt100's input buffer overflowed. I modified the Berkeley "tset" command to examine the terminals termcap for a ":QS:" entry. This fits in with tset's use of other capital termcap entries for setting delays and such. If the QS entry is there it does the appropriate ioctl to set "restart on control-Q only". Fortunately all our systems had the appropriate ioctl to do this. I suggest you look hard before modifying your kernel. The ioctl may be there but just hard to find. Check the tty(4) man page carefully. I like the tset approach as it makes the change terminal dependent. Terminals without built-in flow control still have the benefit of the restart on any character "feature". Also, as has been mentioned before, this change does not destroy the restart on any character feature. The user of a vt100 never had that feature. Even when Unix sent the characters, the vt100 refused to display them! I can post the diffs to tset but as has been mentioned the ioctl required is very system dependent. I have the changes for the BSD 2.8, 2.9, and 4.1 systems. Even within BSD all three are different. Jerry Aguirre @ Olivetti ATC {hplabs|fortune|idi|ihnp4|tolerant|allegra|tymix}!oliveb!jerry