[Bug-tar] Reproducible archives with --posix (Re: --xattrs makes archives unreproducible)

[Pavel Raiskup]

Hi Zachary, thanks for working on the patch.

On Friday 26 of June 2015 15:37:26 Zachary Vance wrote:
> Archives with extended headers are reproducible

This is not --xattrs related fix, but rather --posix related.  Using
--xattrs/--selinux/--acls GNU tar automatically chooses 'pax' format.

> * I've changed ".%p" in the default headers to .0 instead of stripping the
> component. This is in the hopes that this will maintain some compatibility
> with old parsers.

FWIW, I'm not in favor of diverging from pax specification here.  While
this change is really worth doing, should not we rather first try to
change (relax) the pax specs [1]?  I'm not sure whether the %p string
helps somehow in real world.  If there was some xheader unaware tar
implementation, having the PID in PaxHeaders directory name (after
extraction) is just misleading IMO.

>From [1]:
| If no -o exthdr.name= string is specified, pax shall use the following
| default value:
|
| %d/PaxHeaders.%p/%f

[1] http://pubs.opengroup.org/onlinepubs/009695399/utilities/pax.html

Pavel