[ACL-Devel] tar file format?

[Andreas Gruenbacher]

Linda Walsh wrote:
> 
> Andreas Gruenbacher wrote:
> >
> > Michael Tokarev wrote:
> > >
> > > Does anybody knows how the acl entries should be represented
> > > in tar?
> >
> > The Posix 1003.1e working group did not issue any recommendations. To my best
> > knowledge, there is an improved format being worked on (see the Austin group,
> > <http://www.opengroup.org/austin/>). I don't know anything about the status or
> > the area they will cover. There are also some other issues to be resolved,
> > including maximum file size (there's a limit in tar that's reachable today, for
> > example).
> >
> > Who knows more about this?
> > If you're serious about extending GNU tar you should talk to Paul Eggert
> > <eggert@twinsun.com>, the mantainer of paxutils. Also, some people on this list
> > might have some ideas about it.
> ---
>         Under Irix there is a -M option that is supposed to store all the
> CAP, MAC and ACL information.  It dumps it to 1 specific file, say "/tmp/.foo".
> So if you looked at the tar, you'd find a copy of /tmp/.foo for each file on the
> tape.  When it is unpacked, tar should read the /tmp/.foo after it restores each
> file and set the ATTR block up accordingly.  If you unpacked with a normal
> version of tar that doesn't know about ATTR's, it would just write over /tmp/.foo
> a bunch of times needlessly.  I suppose at the end of an archive an empty /tmp/.foo
> should be written to zero out the last remaining ATTR block info.

We would need to store the attribute values in their external representations as
specified in Posix 1003.1e DS17. Storing the binary values of attributes leads
to nonportable archives. I have no clear idea how tar and related tools could be
tought how to convert to/from external representations of arbitrary file
attibutes (except for hard-coding all these conversions into the tools).


Andreas

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 Andreas Gruenbacher, a.gruenbacher@computer.org
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