Hi Jan,

That all makes sense and answers my question. Ideally we would like to
avoid the intermediate updates as this adds complexity to update logic
(i.e. you have to leap-frog through that for devices that are factory
fresh). Sounds like there are no immediate plans for breaking changes and
I'll keep an eye on the mailing list so I can weigh in. Thank you very much
for taking the time to give such a well thought out answer!

For anyone else who finds this thread later, I also found reference to this
in the documentation
https://rauc.readthedocs.io/en/latest/advanced.html#migrating-to-an-updated-bundle-version
.

Best,
~Matt

On Fri, Jun 5, 2020 at 2:25 AM Jan Lübbe <jlu@pengutronix.de> wrote:

> Hi,
>
> On Thu, 2020-06-04 at 15:02 -0400, Matt Campbell wrote:
> > I'm looking into RAUC for a product, and I was wondering if there are
> > any project goals around the stability of the RAUC bundle format.
> > Specifically, it would be great if all future versions of the rauc
> > binary was compatible will all previous bundle formats, and also that
> > all older versions of the binary can install future created bundles.
> > Obviously that's a big ask, but it'd be great to know what to expect
> > of RAUC in the future. Even a rough idea of how compatibility will
> > play out will help me greatly in evaluating RAUC.
>
> The basic bundle format has not changed so far (squashfs with
> CMS
> signature), which means that newer versions can install old bundles.
> Going forward, any issue with installing old bundles would be
> considered a bug.
>
> Newer RAUC versions have introduced new features and slot types, though
> (such as casync, emmc-boot partitions, MBR partition switching). If you
> use those features, old versions of RAUC won't be able to install those
> bundles. As long as you don't use new features, our intention is that
> bundles created by newer versions will be installable by older
> versions.
>
> There are ideas of introducing a new bundle format to allow streaming
> installation (over the network), but we won't remove support for the
> original format.
>
>
> If there are ever reasons that require an incompatible change, you can
> use a two step migration:
> You can use an intermediate update to ship a new RAUC binary in a
> bundle created by the old version. Then use the newly installed RAUC
> for the real update.
>
>
> Does that answer your questions?
>
> Regards,
> Jan
>
>

-- 
Matthew Campbell
Senior Embedded Systems Engineer
mcampbell@izotope.com

iZotope, Inc.
www.izotope.com