aufs support is deprecated and should be handled on upgrade

[Steve Langasek]

The Ubuntu kernel team has continued to carry aufs support as a sauce patch but there is no known application for this filesystem anymore except for docker deployments using this deprecated storage option.

We can't expect the kernel team to carry this deprecated filesystem indefinitely merely because docker.io upstream hasn't provided a migration path for existing installs. If we can't do a smooth conversion on upgrade of the docker.io package from aufs to another storage backend, then at the very least we need to draw a line and block the upgrades between releases.

So for hirsute we should make use of aufs in the docker config to result in blocking the upgrade in preinst.

We should also add a quirk to ubuntu-release-upgrader, so that on release upgrades this case can be detected before starting the upgrade and causing maintainer script failures in the middle.

We don't really want this change to be SRUed back to prior releases, but this is subject to being revisited if the focal HWE kernel needs to drop aufs support.

[William Wilson (jawn-smith)]

Attached is a debdiff to add a preinst file to docker.io that will stop it from upgrading if containers are using aufs.

[Michael Hudson-Doyle (mwhudson)]

Hi, docker packaging is maintained at https://github.com/tianon/debian-docker/tree/ubuntu so perhaps you could propose this as a change there? (It's possible we should move this to somewhere with a more generic URL -- or already have, but I don't think so)

[Ubuntu Foundations Team Bug Bot (crichton)]

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[Michael Hudson-Doyle (mwhudson)]

Although there's no reason for the deb's preinst to be checking /var/snap/docker/common/var-lib-docker/aufs surely?

[Steve Langasek (vorlon)]

On Wed, Feb 24, 2021 at 01:27:45AM -0000, Michael Hudson-Doyle wrote:
> Although there's no reason for the deb's preinst to be checking
> /var/snap/docker/common/var-lib-docker/aufs surely?

Agreed, that's not part of the deb so out of scope for a docker.io preinst.

[William Wilson (jawn-smith)]

https://github.com/tianon/debian-docker/pull/4

This PR removes the check for the snap aufs dir.

[William Wilson (jawn-smith)]

Per Tianon's suggestion, I have created a NEWS file for aufs-tools to warn users of the deprecation of AUFS.

[Brian Murray (brian-murray)]

I've uploaded the ubuntu-release-upgrader changes for this today.

[Launchpad Janitor (janitor)]

This bug was fixed in the package docker.io - 20.10.2-0ubuntu2

---------------
docker.io (20.10.2-0ubuntu2) hirsute; urgency=medium

  [ William 'jawn-smith' Wilson ]
  * Add a preinst check for aufs storage-driver to fail the upgrade.
    (LP: #1907713)

 -- Michael Hudson-Doyle <email address hidden> Tue, 02 Mar 2021 18:45:16 +1300