Comment 39 for bug 1694159

On the release notes for Artful we should add a about this along the usual Libvirt update info.
There is no release note wiki/template for Artful yet, so I added a tracker for that.

An example could look like:

There was an issue in libvirt (bug 1694159) about handling conffiles when upgrading from Xenial (16.04) to latter releases. This issue lead to duplicate conffiles carrying the old libvirt-bin names/references.
Since Yakkety (16.10) those files are inactive but still around. That is misleading at best - e.g. if users try to modify them and wonder why the daemon do not pick up the changes. Therefore those conffiles will get cleaned up now.
For LTS (16.04) -> LTS (18.04) upgraders, but also for Xenial -> Ubuntu Cloud Archive Pike transitions this will be fine. In those cases there never were inactive duplicates, so the upgrade will move and retain user configurations as it should have done back in Yakkety.
But users that are already on Yakkety or later will have the duplicate conffiles around and moving those might negatively affect a currently working setup. Therefore in those cases the old conffiles are removed. If there was any custom content present they will be backed up as usual with a .dpkg-bak suffix and the user prompted about that on the upgrade.
In general changes to the affected conffiles are rather rare, so for most users the upgrade will just remove a few old inactive conffiles.