Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-sdd!apollo!brian
From: brian@apollo.HP.COM (Brian Holt)
Newsgroups: comp.sys.apollo
Subject: Re: Apollo won't release rbak/wbak format.  grrr.
Message-ID: <45fe461b.18e92@apollo.HP.COM>
Date: 2 Oct 89 21:21:00 GMT
References: <26979@iuvax.cs.indiana.edu>
Reply-To: brian@apollo.HP.COM (Brian Holt)
Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
Lines: 32

In article <26979@iuvax.cs.indiana.edu> sahayman@iuvax.cs.indiana.edu (Steve Hayman) writes:
>
>"the rbak/wbak format is unpublished and we don't want to give it out."
I'm afraid I don't know anything about the rbak/wbak format, but if I
did I'd send it to you.

>Mind you I suspect that "man 5 tar" doesn't
>tell you the true story of Apollo's tar format, since it doesn't
>mention anything about whatever extensions they've added to support
>Apollo specific information. (see "man 1 tar", description of the "A" option)
Actually, we specifically did use the standard tar format, so that
you can read even -A files on any machine. The solution (how to include
more data without changing the tape format) is a bit of a hack, but
it works. If you write a tape with the -A format, then tar creates
two entries on the tape for every file. One is just the normal 
tar entry, the second is a dummy file (I think it is /tmp/somethingorother)
that contains the extended information. When read by a normal version
of tar, this short file will get created multiple times and the
tape will restore correctly. When read by tar on DomainOS, tar will
notice the shadow file and set the DomainOS attributes according to
its contents. 

I have to confess this hack was my idea, but it was the only solution
that allowed us to mantain complete compatibility with everyone's 'tar'
and still add extra information.

		=brian

P.S. I haven't worked in that group for a couple years, so that's all I know.
-- 
Internet: brian@apollo.hp.com
UUCP:     {decvax,mit-eddie,umix}!apollo!brian