Re: [PATCH] import-tars: ignore the global PAX header

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi brian,

On Mon, 23 Mar 2020, brian m. carlson wrote:

> On 2020-03-23 at 13:08:44, Johannes Schindelin via GitGitGadget wrote:
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > Git's own `git archive` inserts that header, but it often gets into the
> > way of `import-tars.perl` e.g. when a prefix was specified (for example
> > via `--prefix=my-project-1.0.0/`, or when downloading a `.tar.gz` from
> > GitHub releases): this prefix _should_ be stripped.
> >
> > Let's just skip it.
> >
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >     Ignore the global PAX header in import-tars.perl
> >
> >     This problem came up in Pacman-related work, where PKGBUILD definitions
> >     would reference the tarballs downloaded from GitHub, and patches would
> >     be applied on top. To work on those patches efficiently (e.g. when an
> >     upgrade to a new version of the project no longer lets those patches
> >     apply), I need to be able to import those tarballs into playground
> >     worktrees and work on them. I like to use
> >     contrib/fast-import/import-tars.perl for that purpose, but it really
> >     needs to strip the prefix, otherwise it is too tedious to work with it.
> >
> > Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-577%2Fdscho%2Fimport-tars-skip-pax-header-v1
> > Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-577/dscho/import-tars-skip-pax-header-v1
> > Pull-Request: https://github.com/gitgitgadget/git/pull/577
> >
> >  contrib/fast-import/import-tars.perl | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/contrib/fast-import/import-tars.perl b/contrib/fast-import/import-tars.perl
> > index e800d9f5c9c..d50ce26d5d9 100755
> > --- a/contrib/fast-import/import-tars.perl
> > +++ b/contrib/fast-import/import-tars.perl
> > @@ -139,6 +139,8 @@
> >  			print FI "\n";
> >  		}
> >
> > +		next if ($typeflag eq 'g'); # ignore global header
> > +
>
> In general, it isn't safe to do this.  A pax global header contains
> attributes that may live in a normal extended header at a lower
> priority.  So it is valid, for example, to write an mtime field in the
> global header that applies to the entire archive and overrides the
> ustar header block (and is overridden by a normal extended header).
>
> I think we need a different solution for this case.

I agree that we need a different solution for this case.

At the same time, I would like to point out that I am trying to address a
_different_ problem than "we're not using the information contained within
the PAX global header": I want to prevent that header from polluting the
top-level tree.

For what it's worth, my patch does not prevent future patches from using
the information contained within the global header :-)

Thanks,
Dscho