Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!rutgers!lll-lcc!ptsfa!ihnp4!homxb!whuts!mtune!jhc
From: jhc@mtune.ATT.COM (Jonathan Clark)
Newsgroups: comp.unix.questions
Subject: Re: tty watcher
Message-ID: <1310@mtune.ATT.COM>
Date: Tue, 22-Sep-87 02:00:53 EDT
Article-I.D.: mtune.1310
Posted: Tue Sep 22 02:00:53 1987
Date-Received: Thu, 24-Sep-87 01:33:55 EDT
References: <4263@ozdaltx.UUCP> <15136@hi.UUCP> <1178@mtune.ATT.COM> <1180@mtune.ATT.COM> <28020@sun.uucp>
Reply-To: jhc@mtune.UUCP (Jonathan Clark)
Organization: AT&T ISL Middletown NJ USA
Lines: 40

>> 	/* output */			/* input */
>> 	mblk_t *dup;			mblk_t *dup;
>> 	dup = copymsg(mp);		dup = copymsg(mp);
>> 	putnext(up_to_monitor,dup);	putnext(up_to_monitor,dup);
>> 	putnext(down_to_device,mp);	putnext(up_from_device,mp);
>
>this means that *everything* going up and down the stream gets sent upstream

Well, the original requirement was that *everything* the user typed or
was sent be seen on the monitoring terminal!

>It's straightforward enough to duplicate only the interesting messages with
>a switch statement, but it does increase the line count a bit more....

And I did mention that the 'guts' of the procedure could be done in
three lines. Such trivialities as ensuring that the monitor tty is
useable after unusual conditions are left as an exercise for the
enthusiastic streams programmer :-)

>I could imagine some packaged systems supplying a prebuilt kernel or kernels.

I can imagine this as well although I understood that the SVR3 licence
forbad this. I'm willing to be corrected by anyone who's actually
seen one though.

>Umm, no, it doesn't.  I said "consist(s) *solely* of a user-mode program that
>drops on top of a *non-hacked* UNIX system."

You're right. I withdraw the comment. Although I personally believe that
any streams modules *ought* to be user-level code, and that an
experimental streams module shouldn't wreck the rest of the kernel when it
falls over. Of course this would mean that you'd need more than two
mutually protected address spaces. (Does this violate POSIX?)

How about agreeing on 'come the revolution, this *will* be easy'?
-- 
Jonathan Clark
[NAC,attmail]!mtune!jhc

The Englishman never enjoys himself except for some noble purpose.