Re: Supporting arbitrary file attributes

[Paul Eggert]

> From: Mike Gerdts <address@hidden>
> Date: 30 Mar 2002 23:32:59 -0500
> 
> A common problem with each vendor's version of tar is that it is unable
> to support things like ACL's, extended attributes, etc. effectively. 
> Furthermore, if one vendor comes up with a solution for the problem and
> an analagous structure exists on another vendor's platform, there is no
> guarantee that the information can be transported via a tar, cpio, or
> any other known cross-platform utility.

Some of these problems have been fixed in POSIX 1003.1-2001.  Have
you taken a look at its specification of tar and pax format?

You can read the POSIX 1003.1-2001 spec online at:
http://www.UNIX-systems.org/version3/online.html

Registration is required, the terms are here:
http://www.opengroup.org/onlinepubs/terms.htm

Look at the 'pax' command for a description of the new standard
formats, in particular the pax Interchange Format.

> A slightly more complicated example would be to store Solaris Access
> Control Lists (ACLs).

There's no standard for ACLs, unfortunately.  Have you looked at how
Solaris 9 etc. do these things?  No sense reinventing the wheel.

> Tar implementations that are aware of this extensible header format that
> do not support a particulare extensible feature should emit a warning
> when the attributes cannot be assigned to the file.

The pax Interchange Format addresses this issue to some extent.

> Am I describing a free utility that already exists?

Not as far as I know.  Nobody has had the time to work on this stuff yet.