Now that the deb files can reside in different places sorting them leads
to subtil differences in the order and hence the created chroot. apts
unpack order on the other hand might not be a good order (but why would
one sorted from a to z be one?), but it is far more stable as it is
independent on the filenames.
As long as you can make it so that the same path to the deb file works
inside and outside of the chroot using file:// as a mirror is no longer
a problem with the previous work.
Guessing filenames is boring. What if we could ask apt to tell us which
debs it downloaded (or found lying around elsewhere) directly? Turns out
we can rather easily avoiding a bunch of guesswork.
EIPP stands for "External Installation Planner Protocol" and is rather
similar to EDSP but with the clear advantage that we can extract the
information we need more easily as we can tell apt to write the file for
us rather than playing solver-in-the-middle and the problem space is
much smaller meaning less data for apt to generate and to pass through
our hands.
The idea here is simply that every package which doesn't have a Status
field in EIPP has the uninstalled status and the only reason its is part
of the EIPP request is that we want to change this by installing it.
That could be verified via the Install header at the start of the
request, but this commit doesn't implement that.
Note that this means we need "more" than the download-only mode can
provide: Either a simulation or "the real deal". Except we modify the
later to be a fancy no op.
