Re: Streamlining backports

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Hi Ernesto:

I fully concur with what Loic wrote, and just to add to that:

Years ago, a lead developer gave us some general principles that all backports
should ideally follow. These are codified:

https://github.com/ceph/ceph/blob/master/SubmittingPatches-backports.rst#general-principles

but I think it's worth quoting them here. Each backport is supposed to specify:

1. what bug it is fixing
2. why this fix is the minimal way to do it
3. why does this need to be fixed in <release>

Now, how good we are, as a project, at adhering to these principles is already
pretty questionable. How will introducing more automation help us improve?
Or maybe we should change the principles to say: "the Ceph project encourages
commits to be backported from master indiscriminately without any justification
or risk analysis"?

I guess we would not change the stated principles as suggested, but I still
think that, when deciding what kind of automation to introduce, we should ask
ourselves questions like:

How stable are our "stable" releases?
Do we value stability over features, or vice versa?
How often does the drive to backport stuff introduce regressions?
How to gauge the riskiness of a given backport?
Do the answers to these questions vary from one component to another, or can
answers be formulated on a project-wide basis?

Backporting stuff is necessary, but also risky. Automation, I think, can
actually increase the frequency with which we unintentionally introduce
regressions into stable releases because

* automation, if successful, might tend to increase the overall number of
  backports
* automation cannot provide any justification or estimate of risk, so it might
  also increase the number of backports that lack any justification or
  estimation of risk

I'm skeptical of the value of labels, but I do think it would be useful to have
Jenkins jobs checking:

1. whether the commits being cherry-picked are really in master
2. whether the master commits cherry-picked cleanly
3. whether the backport PR contains the same number of commits as the master PR

These couldn't be "mandatory" checks because there are plenty of exceptions, but
I think having this information there would be useful for reviewers (but I don't
review backports so I don't know for sure).

Nathan
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