Re: A radically different proposal for differential updates
- Date: Wed, 16 Aug 2017 03:25:23 +0200
- From: Guillem Jover <guillem@xxxxxxxxxx>
- Subject: Re: A radically different proposal for differential updates
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
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.