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Re: [Bug-tar] xattr support on Linux

From: Tim Kientzle
Subject: Re: [Bug-tar] xattr support on Linux
Date: Wed, 3 Oct 2012 08:11:53 -0700

On Oct 3, 2012, at 5:01 AM, Pavel Raiskup wrote:

>> FWIW, both star and bsdtar support xattrs on Linux.
>> It would be nice if GNU tar were compatible with those existing
>> implementations.
> Thanks Tim, yes -- xattr-patched GNU tar would be unable to extract
> extended attributes from archives created by BSD tar now.  In BSD tar
> pax headers you are using base64 encoding for xattr values *but* in
> different namespace --> so it will be very easy to allow GNU tar unpack
> also BSD tar archives.  I missed that fact and I'll address that later.


bsdtar also URL encodes the xattr name when building the pax property
name.  This ensures the final key will be entirely ASCII (and hence will
not cause any problems with readers that expect all keys to be valid UTF-8).

I can point you to the code in libarchive that handles this if you want
a detailed reference.  (The code is BSD-licensed; you're welcome
to copy it if you wish.)

> Otherwise, GNU tar should be compatible with star both ways because patch
> for GNU tar adopted pax headers encoding from star and I checked it
> before.  And ACLs should be BSD tar <=> GNU tar <=> star both way
> compatible.

Excellent! Thanks for your care.  Among other things, this means
that a number of other applications built on libarchive will
be fully compatible at this level.

With such proven interoperability, perhaps someone should
propose some of these extensions to the Austin Group for
standardization?  ;-)


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