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

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

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Hi René,

On Mon, 23 Mar 2020, René Scharfe wrote:

> Am 23.03.20 um 14:08 schrieb Johannes Schindelin via GitGitGadget:
> > 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.
>
> git archive uses a global pax header to pass the ID of the archived
> commit as a comment, and for mtime values after 2242-03-16.  Ignoring it
> in a simple importer seems reasonable for now, but I don't understand
> how this relates to prefixes.

The tar importer in `contrib/fast-import/import-tars.perl` has a very
convenient feature that I took for public knowledge: if _all_ paths stored
in the imported `.tar` start with a common prefix, e.g.
`my-project-1.0.0/` as indicated in the commit message (or `git-2.26.0/`
in the tar at https://github.com/git/git/archive/v2.26.0.tar.gz), then
this prefix is stripped.

This feature makes a ton of sense because it is relatively common to
import two or more revisions of the same project into Git, and obviously
we don't want all files to live in a tree whose name changes from revision
to revision.

Now, the problem with that feature is that it breaks down if there is a
`pax_global_header` "file" located outside of said prefix.

> Is it because the header is treated as a regular file with the full path
> "pax_global_header" (independently from any prefix for actual files) and
> can thus be placed outside the expected destination directory?

Exactly.

Thanks,
Dscho

>
> Thanks,
> René
>
>