What prevents analog of lvconvert --mergethin?

[decalek]

In the LVM2 variant of dm-thin managament, a user creates thin snapshot with:

lvcreate --snapshot x800/kube2-srv --name kube2-srv-snap02

and swaps its origin online (given not busy devices) with:

lvconvert --mergethin x800/kube2-srv-snap02

If I understand correctly, Stratis (by design) performs snapshot reversion only at pool startup?

What underlying obstacles prevent online dm reconfiguration in Stratis snapshot revert?

[jbaublitz]

@bmr-cymru @mulkieran I think you would be more qualified to answer this question.

[bmr-cymru]

@jbaublitz thanks for the tag!

What underlying obstacles prevent online dm reconfiguration in Stratis snapshot revert?

Nothing at all; just that it was not implemented when the feature was first added: doing it at pool activation time is always safe, and requires no "busy" check. It's an entirely reasonable (and likely simple) RFE.

The major motivator for the feature was a desire to support this in Snapshot Manager, to give feature parity with the LVM plugins. In our case, the volumes are almost always in use at the time the revert is issued (because they typically include the volumes the system is running from), so we were perfectly happy with the simpler initial implementation to begin with.

I thought I'd already filed an issue to do the online revert when possible, but I am not finding it right now; possibly it was just a comment in the original issue/PR (but it's easy to write, both the RFE & the code changes should be quite straightforward).