Re: tar extract changed since netbsd-8? (extracting sets over running system)

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Tue, Nov 12, 2019 at 08:25:46AM -0500, Greg Troxel wrote:
> David Brownlee <abs%absd.org@localhost> writes:
> 
> > On Tue, 12 Nov 2019 at 11:33, Jaromír Doleček <jaromir.dolecek%gmail.com@localhost> wrote:
> >>
> >> Le mar. 12 nov. 2019 à 12:05, Martin Husemann <martin%duskware.de@localhost> a écrit :
> >>>
> >>> Not seen this locally, but that would be the switch to bsd/libarchive tar.
> >>> Maybe it does not unlink files before extraction and replaces them in-space?
> >>>
> >>> I do the same kind of updates, but usually on a very quiet system.
> >>>
> >>> The crashes you see are from other running processes? Joerg would likely
> >>> say: "don't do that" ;-)
> >>>
> >>
> >> I thought we do unlink by default, I think I remember a commit to that effect in past. The unlink is very useful default behaviour of GNU tar. In-place overwrite is very rarely the wanted behaviour.
> >
> > Aha thanks!
> >
> > I would argue the switch to unlink no longer being the default is a
> > regression. If its mandated by standards or we're the only outlier
> > then it probably makes sense to switch, but otherwise its sprinkling
> > occasional non deterministic breakage across a bunch of scripts which
> > previously ran fine on NetBSD.

It does not force an unlink first, but will unlink if there is a
conflict. So the question would be why open(2) with O_CREAT|O_EXCL
doesn't fail.

> I'm not quite clear on 'unlink by default', but it seems to me the
> replacement files should be written to a temporary name and then
> renamed() into place so the file is either the old version or the new
> version.

That would dramatically increase the time it takes for an untar for
little to no gain.

Joerg