Re: support for translators in tar

[Paul Eggert]

> Cc: bug-tar@gnu.org, bug-hurd@gnu.org
> Keywords: Hurd,tar,passive 
> translator,file,format,bits,stat,showtrans,permissions,mode_t,author,ls
> Supersedes: <87lmjkmlzz.fsf@Astalo.y2000.kon.iki.fi>
> From: Kalle Olavi Niemitalo <kon@iki.fi>
> Date: 12 Sep 2001 19:15:08 +0300
> 
> [I already typed this once but lost power before sending.  :-(
> This time, I ensured auto-save-mode is on.]
> 
> Paul Eggert <eggert@twinsun.com> writes:
> 
> > What does 'ls -l' do?  Users will probably want 'tar' to do something 
> > similar.
> 
> It starts the passive translator and gets the stat data from that.

Tar should probably do the same, then, right?  Basically, 'tar' should
save the same thing that 'ls -l' does -- that's what normal users expect.

> > What 'ls' switch is used to see a translator rather than to invoke it?
> > What does the 'ls' output look like in that case?
> 
> There is no such switch,

Perhaps it would make more sense to work on 'ls' first, before 'tar',
as you can gain experience faster with 'ls' to see what the right
switches are, and what is the most convenient in practice.

> Can these be added in such a way that older tars can still read
> Hurd tar archives?

The latest draft of the next POSIX standard, POSIX 1003.1-200x d7,
specifies a new tar format that GNU tar does not yet implement.  This
tar format allows extensions, and there's room in it for the sort of
thing that you describe.  It won't be a small job to add this, though,
since tar needs support for both the new tar format and the GNU
extensions.  I haven't yet found anybody with enough free time to do
this.

The new format attempts to cater to older tars, not entirely
successfully in my opinion.