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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.bugs.4bsd,comp.unix.wizards
Subject: Re: tmscp tape drives give "hard error" on reading too small a record
Message-ID: <6368@mimsy.UUCP>
Date: Mon, 20-Apr-87 14:29:42 EST
Article-I.D.: mimsy.6368
Posted: Mon Apr 20 14:29:42 1987
Date-Received: Tue, 21-Apr-87 03:15:05 EST
References: <1681@husc6.UUCP> <2412@ulysses.homer.nj.att.com> <1696@husc6.UUCP>
Followup-To: comp.unix.wizards
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 20
Keywords: tmscp, TU81, DEC
Xref: mnetor comp.bugs.4bsd:317 comp.unix.wizards:1978

In article <1696@husc6.UUCP> dudek@endor.harvard.edu (Glen Dudek) writes:
>... but UNIX semantics for raw tape devices require this behaviour

I do not think so:

>(at least, all such raw tape drivers I've ever seen behave this way).

All save one.  The TU78 driver in 4.[23]BSD gives ENOMEM errors when
reading with too small a block size.

>I found this problem when a remote software installation broke because the
>installation assumed 'dd if=/dev/rmt4 of=/dev/null' would successfully
>skip a tape file independent of blocksize.

I believe the `proper' way to skip a file is to use the magtape ioctls:
`mt -f /dev/rmt4 fsf'.  Obviously this will not work on systems without
such ioctls.  (So it goes.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	seismo!mimsy!chris	ARPA/CSNet:	chris@mimsy.umd.edu