merge snapshotter override logic

[BenTheElder]

I think this should fix #2987

[BenTheElder]

/hold

[aojea]

/assign @AkihiroSuda

he is the expert here

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: AkihiroSuda, BenTheElder

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[aojea]

should we unhold #2987 (comment)?

[BenTheElder]

Yes. We just deduped the logic a bit to improve prioritizing selecting the right backend.

On containerized ZFS native is the safe fallback, native actually works anywhere but is not as performant.

If kind is running on fuseblk we can pretty safely assume fuse overlafys

Otherwise we check userns and overlayvs vs fuse overlayfs

otherwise overlayfs is the preferred default.

we:

• dropped trying to use fuse overlayfs on ZFS per the bug
• check for this case before checking the userns case, because native will also work fine there

[BenTheElder]

/hold cancel
/override pull-kind-e2e-kubernetes
(unrelated failure, known issue with an actual Kubernetes regression affecting more than kind being reverted upstream)

[k8s-ci-robot]

@BenTheElder: Overrode contexts on behalf of BenTheElder: pull-kind-e2e-kubernetes

In response to this:

/hold cancel
/override pull-kind-e2e-kubernetes
(unrelated failure, known issue with an actual Kubernetes regression affecting more than kind being reverted upstream)

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