Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!cmcl2!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn )
Newsgroups: comp.unix.wizards
Subject: Re: Ultrix tape job is unkillable!
Message-ID: <9221@smoke.BRL.MIL>
Date: 17 Dec 88 08:39:24 GMT
References: <476@larry.UUCP> <43200057@uicsrd.csrd.uiuc.edu> <8555@alice.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 16

In article <8555@alice.UUCP> debra@alice.UUCP () writes:
>An identical machine with Unix 9Vr2 does not have this problem. So it clearly
>is something in the Berkeley device driver.

That wouldn't surprise me very much.  VAX (and PDP-11) magtape drivers
have been pretty horrible in most UNIXes I've seen, partly due to the
tendency of most controllers to generate one interrupt when a rewind
(for example) command is accepted, and another when BOT is reached.
This implies that some state must be maintained in the driver, and
you know how notoriously easy it is to get into trouble doing that.

It could be much worse -- when I was using a prerelease of VAX/VMS
(as a DEC subcontractor) ages ago, I took the TE16 off-line manually
while it was rewinding (in order to be sure it wouldn't be overwritten,
since it still had the write ring installed), and the WHOLE SYSTEM
wedged until the rewind completed.  I nearly died laughing..