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Re: A radically different proposal for differential updates




Hi!

While this sounds indeed interesting, I think it's impractical for at
least the two reason below:

On Tue, 2017-08-15 at 09:26:24 +0200, Christian Seiler wrote:
> AFAQ (Anticipated frequently asked questions):
> 
> Q: How can you reconstruct a tarball from the installed system? Won't
>    that change quite a bit? How will you ever be able to get more than
>    just a couple of similar chunks out of this scheme?
> A: If you modify stuff on your system: yes, the tarball you can
>    generate from that will differ from the tarball that is in the .deb.
>    However, as we want our .deb files to be reproducible, we are posing
>    additional restrictions on the tarballs inside .deb files that are
>    not part of the .tar standard. Most importantly the file ordering
>    has to be well-defined - and currently this is done via sorting in
>    the C locale. If we recreate the tarball from the system with these
>    same constrains, we should ideally get an identical tarball back if
>    no files are changed.

Unforuntately that's not the case. Reproducible .debs are based on
using the same tool versions as were used when originally generating
those .deb:s.

The .deb format keeps being updated, for example it changed default
compressor recently-ish. I expect it will keep evolving. And what's
installed on the system gives no information about what dpkg version
was used to generate its original .deb.

> Q: What about tools like debootstrap etc.?
> A: I believe it should be possible to implement this format in
>    debootstrap in a relatively straight-forward manner.

As Julian has mentioned, tons of things expect actual .deb packages
to be around, starting with humans doing stuff like
«wget URL && dpkg -i foo.deb» or dget, and tooling, etc.

Thanks,
Guillem