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Path: utzoo!linus!philabs!sbcs!bnl!stern
From: stern@bnl.UUCP (Eric Stern)
Newsgroups: net.unix
Subject: Re: Is anybody *USING* ANSI tapes on UNIX (label handling)
Message-ID: <919@bnl.UUCP>
Date: Mon, 15-Apr-85 01:01:27 EST
Article-I.D.: bnl.919
Posted: Mon Apr 15 01:01:27 1985
Date-Received: Sat, 20-Apr-85 01:22:30 EST
References: <504@sal.UUCP> <533@spp2.UUCP>
Distribution: net
Organization: SUNY StonyBrook
Lines: 41

> In article <504@sal.UUCP> jf@sal.UUCP (Johan Finnved) writes:
> >Possible implementation suggestions:
> >
> >... It starts by
> >rewinding the tape and checking its volume label in order to make sure
> >that this user (real uid) has really the right to use this tape. ...
> >Does anybody have ideas on what to put in the fields for Owner
> >Identifier (in VOL1 lables), Accessibility  (In VOL1 and HDR1-EOV1-EOF1
> >labels) and System Code (in HDR1-EOV1-EOF1 labels) ?
> 
> Just be sure that, for those cases when I take my tape to your site, I
> can read & write to my tape without requiring recourse to superuser
> capabilities.  (The loginid & userid probably will be different.  Very
> often, my userid on my system will be assigned to someone else on
> your system.)

The volume label contains a field for accessability and a
machine dependent field for owner identification.  In VMS,
if the system determines that the tape was written on a DEC
system, the owner identification field contains the owner's
identity and volume protection information.  Volume protection
can be granted in the same way as file protection works, so
read and write permission can be allowed or disallowed to
members of the owners group, and the general world.
At mount time, the information is checked and access is
granted/denied appropriately.  Of course someone with system
priviledges can overide this.  I presume that if the volume was
not generated on a DEC computer, the system allows full access.

Because the user identifier and file protection concepts are
so similar on UNIX and VMS, something similar ought to be
possible on UNIX.  The information on what VMS writes in tape
labels in contained in the back of the RMS reference manual.
This includes the standard ansi stuff as well as the DEC
specific stuff.  They also give the formats for laying out
tapes multiple tape volume sets, and multiple volume files.

				Eric G. Stern
				..!philabs!sbcs!bnl!stern
				stern@bnl.arpa
				stern@bnl.bitnet