Comment 10 for bug 1890248

With my SRU hat on: it's always a bit of a tricky situation whether we accept a completely new upstream version backport for a stable LTS series. In case of mdadm it's especially tricky, considering that 4.1 has been tagged (released) 3 years ago, meaning 4.2 has 3+ years of changes bundled up. And that always carries risks of regressing many users.

Per the SRU policy [1], generally we allow new upstream microreleases into stable series which carry changes fitting SRU criteria if the upstream project has:
 * a reliable and credible test suite for assuring the quality of every commit or release,
 * the tests are covering both functionality and API/ABI stability,
 * the tests run during package build to cover all architectures,
 * the package has an autopkgtest to run the tests in an Ubuntu environment against the actual binary packages

So these are the general policy guidelines. We can of course evaluate every project case-by-case, and not all of these points need to be strictly true (it would be hypocrisy to say we STRICTLY require that, as there are exceptions that we approved). But in general the idea is: we need to make sure that the upstream project has sufficiently strong testing story to make sure a minimal number of users can be potentially affected by any ABI/API breakages and/or general regressions.

I would appreciate some help in getting a better understanding of the mdadm situation with this in mind. Things I'd like to know:
 1) I see that mdadm runs its tests/ as autopkgtests. How thorough are those tests? How often are new test cases added by upstream?
 2) How many autopkgtests of other packages are triggered when mdadm is uploaded?
 3) What are the bugfixes (and possibly also new features) that are added between 4.1 and 4.2?
 4) Besides the merit of having many different bugfixes from 4.2, is there a legitimate reason why we want to have mdadm 4.2 in focal? Is there a particular bugfix/feature we need that would otherwise be a pain to cherry-pick? (this is not particularly a requirement, but will help in decision making)

Thanks!

[1] https://wiki.ubuntu.com/StableReleaseUpdates#New_upstream_microreleases