Obsolete earlier packages due to version bump

[behlendorf]

Motivation and Context

Issue #11230.

Description

In order for package managers such as dnf to upgrade cleanly after
the package SONAME bump the obsolete package names must be known.
Update the new packages to correctly obsolete the old ones.

@aerusso I believe alien understands the obsoletes tag for the upstream
packaging, but I wanted to make sure you have a similar fix in the Debian
packages.

How Has This Been Tested?

Performed a dnf upgrade on Fedora and CentOS 8 and verified the
old packages were correctly detects as obsolete and replaced.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[aerusso]

Debian handles this slightly differently: we keep the old libraries in the repository until there are no reverse dependencies, after which the libraries will be "autoremoved as cruft." Normally, this happens after periodic package rebuilds. However, for ZFS it will be much faster: there are no Debian packages that depend on any of the libraries shipped by ZFS (besides ZFS itself).

The packages will then become obsolete, and should be automatically removed from user systems.

Debian goes to great lengths to make sure old libraries remain coinstallable to support old software, so normally old libraries are left around to support older software. I probably won't put any specific conflicts in place because it might represent an uphill battle for no gain.

That is, unless there is danger in having the old libraries around. For instance, if the newer kernel interface somehow is dangerously backwards-incompatible with the old libraries.

[behlendorf]

Thanks for the explanation. Then it sounds like this should be fine. There's no issue with having the old libraries around.