Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!philabs!nyit!rick
From: rick@nyit.UUCP (Rick Ace)
Newsgroups: net.unix,net.unix-wizards
Subject: Re: need help with multi-reel cpio
Message-ID: <236@nyit.UUCP>
Date: Tue, 6-May-86 10:54:44 EDT
Article-I.D.: nyit.236
Posted: Tue May  6 10:54:44 1986
Date-Received: Thu, 8-May-86 07:36:45 EDT
References: <520@sdcc13.UUCP> <461@ncr-sd.UUCP> <1241@ulysses.UUCP> <446@brl-smoke.ARPA>
Organization: NYIT Computer Graphics Lab., Old Westbury, N.Y.
Lines: 43
Xref: linus net.unix:7133 net.unix-wizards:14956

Doug Gwyn writes:
> I prefer Greg's suggestion over Griff's.  There seem to me to be
> two ways to handle magtapes on UNIX:  (a) make them do the right
> thing to fit the generalized idea of "file";  (b) supply special
> magtape-handling bells and whistles.  I've managed in the past
> to make method (a) serve quite well, even for such things as
> ANSI standard magtapes; since I believe in the generalized file
> approach, that's the method I recommend.  Approach (b) is not
> really necessary, in my opinion.  But whatever approach is used,
> it should be done RIGHT, which has not traditionally been the
> case with UNIX magtape drivers.

If you have method (b) only, you can simulate method (a) in user-mode
code.  The reverse is not necessarily true.

Perhaps for your requirements, method (a) is adequate.  However,
those who have worked extensively with magtapes will appreciate
having access to method (b) as well, particularly when trying
to read a non-ANSI (or almost-ANSI) tape that was written by a
non-UNIX host.

All tape drives I've met support these primitive operations:

	Read physical record (or tape mark) and return its length
	Write physical record of software-specified length (before,
	 at, and after the EOT reflector)
	Write tape mark (before, at, and after the EOT reflector)
	Rewind
	Detect transition into the EOT region (the tape beyond the reflector)

UNIX magtape drivers should offer these functions as a bare minimum.
Supporting the generalized notion of a "file" is also useful, but
there are some instances where you want to tell the operating system
to get out of the way and provide "hands-on" access to the tape.

-----
Rick Ace
Computer Graphics Laboratory
New York Institute of Technology
Old Westbury, NY  11568
(516) 686-7644

{decvax,seismo}!philabs!nyit!rick