RFC: Major-to-major OS update only

[agners]

Context

At times OS changes requires some migration. To make migration maintainable, we typically assume upgrades from one major to the next.

In a particular case, ova and generic-x86-64 updates from 6.1 and before cannot be done to 7.6 and beyond (read the details in home-assistant/operating-system#1889).

Decision

We should prevent upgrades which skip major versions. We do not have metadata about older release readily available, hence that does not allow us to jump to the latest version of a particular major release. However, we do know the first version of a particular major release, hence we can enforce an update to that version only, e.g.:

• 6.0 -> 7.0
• 6.6 -> 7.0
• 7.0 -> 8.0

[agners]

In discussion, jumping to x.0 releases is problematic for two reasons:

• We cannot address a bug in the upgrade path of a x.0 release
• Some people might be inclined to not upgrade due to releases ending with .0 having bad reputation 😅

Proposed solution is to upgrade to the latest release of the next major release. For that to work we need to have a dictionary which allows to loop up what the last release of a particular series is, e.g.

  "hassos-upgrade": {
    "6": "6.6",
    "5": "5.13",
  }

The logic would check as follows:

1. Get major of current release
2. Lookup major in hassos-upgrade
3. If listed and match: Goto 6
4. If listed and doesn't match: Offer upgrade to that version
5. If not listed: Offer upgrade to latest as per hassos dictionary.
6. Lookup major + 1 in hassos-upgrade
7. If listed: Offer upgrade to that version
8. If not listed: Offer upgrade to latest as per hassos dictionary.

This would mean following upgrade paths:

• Starting at 6.1: -> 6.6 -> 7.6
• Starting at 6.6: -> 7.6