Re: How to distinguish .udeb files from regular .deb files?

[Guillem Jover <guillem@debian.org>]

Hi!

On Fri, 2016-08-19 at 13:47:15 +0200, Philipp Hahn wrote:
> I accidentally called "dpkg-name" on some *.udeb files and they got
> renamed to .deb.

Yes, and the reasons are a bit ugly, so you might want to skip the
following paragraph…

This is the consequence of the half-assed integration of .udebs into
the lower-level deb toolchain. I started merging support into dpkg
years ago, but got into some technical disagreement with the
debian-installer team at the time (#452273), and while the discussion
got a bit heated, I think it had definitely not yet reached a point of
no-return, it then was referred to the tech-ctte by an uninvolved party
for no good reason (#575059), at which point I lost any kind of
motivation and before they imposed any kind of decree on any of
the "sides", I reverted the change and stopped any further work on
integrating udebs natively in dpkg. So that's what you are seeing above.

> Looking inside dpkg-name, it tries to evaluate "Package-Type" [1], but
> that is not contained in the control file of the binary package, so
> always evaluates to "deb":
> > 123     my $type = $fields->{'Package-Type'} || 'deb';

Right, “deb” is the default type so normal .deb packages will not have
that field, “udeb” is special cased in dpkg-genchanges to avoid including
that “huge” field, but any other value would get the field in the binary
package:

,--- dpkg-genchanges ---
my $pkg_type = $pkg->{'Package-Type'} ||
               $pkg->get_custom_field('Package-Type') || 'deb';

if ($pkg_type eq 'udeb') {
    delete $fields->{'Package-Type'};
    delete $fields->{'Homepage'};
} else {
    for my $f (qw(Subarchitecture Kernel-Version Installer-Menu-Item)) {
        warning(g_('%s package with udeb specific field %s'), $pkg_type, $f)
            if defined($fields->{$f});
    }
}
`---

I also thought I had added support for Package-Type to dpkg-deb but it
seems not, I'll be doing so, but of course that will still not help
with .udebs, as per above.

> Is there some other (preferred) way to identify .udeb packages?

> 1. "Section: debian-installer"?

This is the current best "heuristic", but it still feels wrong, as the
true marker for whether a package is a deb or something else is the
Package-Type field.

Thanks,
Guillem