Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!gatech!ulysses!ggs
From: ggs@ulysses.homer.nj.att.com (Griff Smith)
Newsgroups: comp.unix.wizards
Subject: Re: Ultrix tape job is unkillable!
Summary: broken device drivers/hardware
Message-ID: <11027@ulysses.homer.nj.att.com>
Date: 20 Dec 88 17:30:45 GMT
References: <476@larry.UUCP> <43200057@uicsrd.csrd.uiuc.edu>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 42

In article <43200057@uicsrd.csrd.uiuc.edu>, kai@uicsrd.csrd.uiuc.edu writes:
> 
> > Written by jwp@larry.UUCP:
> > ...
> > so instead of interrupting the process with cntl/C, I pop the
> > drive off-line (thinking the jobs will abort).  Later, I find
> > the "readtape" job hanging around with a priority of -5, and
> > I couldn't kill it.
> 
> This problem is not specific to Ultrix.  I've found the exact same thing
> occurs on VAX BSD unix, Sequent Dynix, and Alliant Concentrix.  The only
> thing that seems to work is a reboot.

It's not just the brand of operating system; specific drives may work
better than others.  The 4.3BSD device driver for the TU78 tape drive
should have no problem with a drive going off-line; the error recovery
is implemented to follow the procedures described in DEC's TM78
documentation.  I tested the driver with all the nasty cases I could
think of, including dropping power to the tape controller while a tape
was in motion.  The driver survived on a VAX 11/785, but a power
problem on a VAX 8650 caused an interrupt loop that required a
re-boot.  You might try tripping power breakers to see what happens,
but not when you aren't willing to take a crash.

> Is this a problem in the device driver, kernel process management, or
> something else entirely?
> there ought to be a way to have the OS force the event to occur or fail.

The problem is that people who write tape device drivers often don't
give a damn about error recovery.  There has also been little interest
in defining consistent error recovery semantics, even WITHIN offerings
from a single vendor.  Some tape drives also make it difficult to deal
gracefully with errors.  I think 4.4BSD will have a close approximation
of reasonable behavior; I'm surprised that Ultrix doesn't yet.

> Patrick Wolfe  (pat@kai.com, kailand!pat)
> System Manager, Kuck and Associates, Inc.
-- 
Griff Smith	AT&T (Bell Laboratories), Murray Hill
Phone:		1-201-582-7736
UUCP:		{most AT&T sites}!ulysses!ggs
Internet:	ggs@ulysses.att.com