[Merge] ~xnox/ubuntu-release-upgrader:ignore-base-tasks into ubuntu-release-upgrader:ubuntu/master

[Dimitri John Ledkov]

Dimitri John Ledkov has proposed merging ~xnox/ubuntu-release-upgrader:ignore-base-tasks into ubuntu-release-upgrader:ubuntu/master.

Commit message:
DistUpgradeCache: Ignore BaseMetaPkgs' & obsolete tasks
 during server upgrade

ubuntu-minimal and ubuntu-base are forced to stay installed via
BaseMetaPkgs / keepBaseMetaPkgs rule during either desktop or server
upgrades. During server upgrades, we try to establish which Tasks are
installed, we do this by iterating all packages and checking if all
packages of a given Task are installed. This is the case for
ubuntu-minimal & ubuntu-standard. But they are not manually-installed
tasks. Instead they are handled with a metapackage only, to allow
alternative implementations of certain components
(i.e. time-daemon). Thus during upgrade we should not force install
those, but instead rely on keeping BaseMetaPkg installed only to
esnure that alternative selections of time-daemons is permitted and is
not changed.

Also, this function might missdetect as obsolete tasks as
installed. For example Task: ubuntu-core should no longer exist, as
the metapackages for it got dropped, but we forgot to remove the
metadata from the archive. If it happens that ubuntu-core appears to
be fully installed, do not try to preserve it on upgrades.

LP: #1872902


Requested reviews:
  Steve Langasek (vorlon)
  Julian Andres Klode (juliank)
  Balint Reczey (rbalint)
  Ubuntu Core Development Team (ubuntu-core-dev)
Related bugs:
  Bug #1872902 in chrony (Ubuntu): "Upgrade to Focal now removes chrony"
  https://bugs.launchpad.net/ubuntu/+source/chrony/+bug/1872902

For more details, see:
https://code.launchpad.net/~xnox/ubuntu-release-upgrader/+git/ubuntu-release-upgrader/+merge/382970

DistUpgradeCache: Ignore BaseMetaPkgs' & obsolete tasks
 during server upgrade

ubuntu-minimal and ubuntu-base are forced to stay installed via
BaseMetaPkgs / keepBaseMetaPkgs rule during either desktop or server
upgrades. During server upgrades, we try to establish which Tasks are
installed, we do this by iterating all packages and checking if all
packages of a given Task are installed. This is the case for
ubuntu-minimal & ubuntu-standard. But they are not manually-installed
tasks. Instead they are handled with a metapackage only, to allow
alternative implementations of certain components
(i.e. time-daemon). Thus during upgrade we should not force install
those, but instead rely on keeping BaseMetaPkg installed only to
esnure that alternative selections of time-daemons is permitted and is
not changed.

Also, this function might missdetect as obsolete tasks as
installed. For example Task: ubuntu-core should no longer exist, as
the metapackages for it got dropped, but we forgot to remove the
metadata from the archive. If it happens that ubuntu-core appears to
be fully installed, do not try to preserve it on upgrades.

LP: #1872902

-- 
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~xnox/ubuntu-release-upgrader:ignore-base-tasks into ubuntu-release-upgrader:ubuntu/master.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: review-diff.txt
Type: text/x-diff
Size: 1729 bytes
Desc: not available
URL: <https://lists.ubuntu.com/archives/ubuntu-reviews/attachments/20200426/5443d5e8/attachment-0001.diff>