store: lock additional store before validating image

[flouthoc]

• We must lock store before doing any operation if its not the default imagestore.
• Refactor and address some comments from: store,imagestore: treat graphRoot as rwImageStore to support Delete #1578

How to verify ?
Tests from https://github.com/containers/storage/blob/main/tests/split-store.bats must pass as-is.

[rhatdan]

@nalind @mtrmac @vrothberg PTAL

[mtrmac]

Thanks! Locking changes LGTM.

I still don’t understand, and can’t find any documentation, why we need this extra write functionality only for deletes at all, (#1578 (review) ), but I guess I’l leave that to the involved parties to deal with.

[flouthoc]

why we need this extra write functionality only for deletes at all

@mtrmac I'll extend this for tag/untag as well, in a new PR. Following PR is just to address the locking race ( which seemed urgent) before anybody starts using this from upstream.

[mtrmac]

I'll extend this for tag/untag as well

(To be clear, my first impression is that we don’t need the functionality, not that we need it universally. But it’s very possible that I don’t understand the goal or problem.)

[giuseppe]

LGTM