[ovirt-devel] new internal stable modules + proposal

[Martin Polednik]

On 29/03/16 11:12 -0400, Francesco Romani wrote:
>Hi,
>
>in the last Vdsm developer call we agreed to promote a few modules in the common repository.
>The common repository provides the additional guarantees over regular modules in lib/vdsm/
>
>- stable API
>- (thus) safe to use across verticals
>
>the planned moves are:
>
>lib/vdsm/schedule.py -> lib/vdsm/common/schedule.py
>lib/vdsm/periodic.py -> lib/vdsm/common/periodic.py
>lib/vdsm/virt/api.py -> lib/vdsm/common/api.py
>
>Question is if those modules should go under common/ or under another subdirectory, maybe infra?

Hi.

I agree that some modules should be kept (and advertised) as stable.

The name 'common' is more suited for such package as 'infra' is very ovirt
specific and could hurt readability and navigation of the project. It does
make sense to structure the project as follows:

lib/vdsm/common
lib/vdsm/virt/common
lib/vdsm/storage/common
lib/vdsm/network/common

Taking extra care taken to avoid 'common junkyard' situation and
making sure that the scope of common corresponds to it's package.

List of modules that I consider public (mostly author/main contributor
of these lately):

lib/vdsm/cpuarch.py
lib/vdsm/cpuinfo.py
lib/vdsm/hostdev.py
lib/vdsm/machinetype.py
lib/vdsm/numa.py
lib/vdsm/osinfo.py
lib/vdsm/udevadm.py

>Lastly, i have a proposal about better handling of those modules.
>
>First, the mere fact a module is placed under lib/vdsm/common provides the extra guarantees I mentioned.
>But should we added more annotations?
>
>for example something like
>
>__API__ = {}
>
>near the top of the module
>
>if this attribute exist, then the module is safe to use across verticals, has stable API and so forth
>(this is _in addition_ to the common/ package, not as replacement).
>
>Like:
>
>__API__ = {
>  "introduced-in": "4.14.0",
>  "deprecated-from": "4.18.0",
>  "removed-at": "4.20.0",
>  "contact": "fromani at redhat.com"
>}
>
>We could refine further this concept if we like it. The idea is to be lightweight as possible while
>carrying all the information we need.

I agree about keeping global metadata in that way, except ideally
using docstrings for better readability (e.g. interactive help()). To
better reflect the needs for granular deprecation and based on our
private discussion on this subject, I'd like to see at least
@deprecated(target_removal_version) decorator. On top of that, we need
properly documented public API and deprecation process.

>Comments welcome as usual
>
>bests,
>
>-- 
>Francesco Romani
>RedHat Engineering Virtualization R & D
>Phone: 8261328
>IRC: fromani
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