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From: jwp@larry.sal.wisc.edu (Jeffrey W Percival)
Newsgroups: comp.unix.wizards
Subject: read(2) won't move TK50 past tape file mark
Keywords: ultrix tk50 unix tapes
Message-ID: <187@larry.sal.wisc.edu>
Date: 23 May 89 23:18:54 GMT
Organization: Space Astronomy Lab, Madison WI
Lines: 35

I have a TK50 tape with 3 80-byte records followed by a tape file mark,
which is in turn followed by many 8192-byte records.  I wrote a little
C program that does a read(2) in a tight loop, and reports the number
of bytes read.    We expect this:

	80 bytes read
	80 bytes read
	80 bytes read
	0 bytes read
	8192 bytes read
	8192 bytes read
	...

Right?  We get this output on a VS2000 with Ultrix 2.2, and a VS2000
with Ultrix 3.0.  However, on 2 of our MicroVAX II's running Ultrix 3.0,
we see this:

	80 bytes read
	80 bytes read
	80 bytes read
	0 bytes read
	0 bytes read
	0 bytes read
	0 bytes read
	0 bytes read
	0 bytes read
	0 bytes read
	0 bytes read
	...

It looks like the read(2) is not getting past the file mark.  This
could be a problem in the C routine read(2), the Ultrix system, or
in the TK50 controller.  Has anyone seen this, or know what's going on?
-- 
Jeff Percival (jwp@larry.sal.wisc.edu)