[libvirt] Bump tar format?

[Daniel P. Berrange]

On Sat, Jun 11, 2016 at 10:14:11AM -0400, Cole Robinson wrote:
> This issue appeared again:

> On 07/22/2015 11:57 AM, Eric Blake wrote:
> > On 07/22/2015 08:44 AM, Andrea Bolognani wrote:
> >>   1. rename the test case, making it shorter;
> > 
> > Works if we can do it, but I agree we should add a syntax check to
> > enforce it.
> > 
> >>
> >>   2. bump tar format from ustar, which has limitations on the length
> >>      of file names, to posix/pax, which has no such limitations.
> > 
> > Might be doable, if RHEL 5 autoconf/automake/tar supports it.  Here's
> > where we switched to ustar:
> > https://www.redhat.com/archives/libvir-list/2012-April/msg01435.html
> > commit 75ad8b67
> > 
> > and even then, we ran into problems with too-long symlinks (which are
> > processed differently than regular files).
> 
> Since RHEL5 support has been dropped for a while now, maybe it's time to
> revisit changing the tar format

Yep, IIUC we should be fine for require pax support for the vintage of
Linux we required.  *BSD should be fine too, so IIUC, their tar version
uses libarchive which supports pax.  Windows has 7-zip which can do pax
and of course cygwin. Finally OS-X has the pax command and support in
the apple archive utility.

So I think we're be fine to require it.

While, we're changing this, I think we should probably take the opportunity
to also switch over to using 'xz' as our compression format, instead of gz.
Consider the 1.3.5 release compressed with different formats:

 35109092  libvirt-1.3.5.tar.gz
 25573966  libvirt-1.3.5.tar.bz2
 12112612  libvirt-1.3.5.tar.xz

Those results seem pretty compelling to me :-)

Regards,
Daniel
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