Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!ames!styx!ptsfa!dual!unisoft!mtxinu!ed
From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: comp.bugs.4bsd
Subject: Re: tmscp tape drives give "hard error" on reading too small a record
Message-ID: <341@mtxinu.UUCP>
Date: Wed, 22-Apr-87 16:44:37 EST
Article-I.D.: mtxinu.341
Posted: Wed Apr 22 16:44:37 1987
Date-Received: Sat, 25-Apr-87 09:59:25 EST
References: <1681@husc6.UUCP>
Reply-To: ed@mtxinu.UUCP (Ed Gould)
Organization: mt Xinu, Berkeley, CA
Lines: 27
Keywords: tmscp, TU81, DEC

>Description:
>	When reading a tape written with a blocksize larger than you are
>	using to read, any tmscp tape drive (e.g., TU81, TK50) will die
>	with a kernel printf "hard error: record data truncated" and an
>	I/O error.  This should not be an error when using the raw device.

That's not a bug, it's the documented - and correct - behavior
of a tape driver.  From mtio(4) on 4.3BSD:

	Each read or write call reads or writes the next record on the
	tape.  In the write case the record has the same length as the
	buffer given.  During a read, the record size is passed back as
	the number of bytes read, provided it is no greater than the
==>	buffer size; if the record is long, an error is indicated.  In
	raw tape I/O seeks are ignored.  A zero byte count is returned
	when a tape mark is read, but another read will fetch the first
	record of the new tape file.

This has been the correct behavior since at least the Sixth Edition.
Some drivers, however, don't conform to the specification.  Please
don't break one that does!

-- 
Ed Gould                    mt Xinu, 2560 Ninth St., Berkeley, CA  94710  USA
{ucbvax,decvax}!mtxinu!ed   +1 415 644 0146

"A man of quality is not threatened by a woman of equality."