feat: support backends that don't allow file owner changes

[Tyler-2]

What it does:

• Checks the actual read/write ability of cache files by the cache user, instead of just checking ownership.

Why does it do that:

• Some storage backends don't support changing of file ownership. What lancache really cares about is whether it can read/write to the files, not whether it owns the files. If the location is read/writable, it's usable. This will allow for a wider variety of backend storage configurations.
• Because it would fix these two issues:
  • Permissions checker too strict #203
  • FORCE_PERMS_CHECK = false does not stop Full Permissions Check at start up #182

Testing done

I've been running with this configmap in my cluster:

apiVersion: v1
kind: ConfigMap
metadata:
  name: lancache-script-permission-check
  namespace: "{{ lancache_namespace }}"
data:
  20_perms_check.sh: |
    #!/bin/bash
    if [ -d "/data/cache/cache" ]; then
      echo "Running fast permissions check - listing files that fail permission check:"
      su - ${WEBUSER} -c 'find /data/cache/cache -maxdepth 1 ! -readable -o ! -writable | grep . && exit 1 || exit 0'
      if [[ $? -eq 0 || "$FORCE_PERMS_CHECK" == "true" ]]; then
        echo "Doing full checking of permissions (This WILL take a long time on large caches)..."
        find /data \! -user ${WEBUSER} -exec chown ${WEBUSER}:${WEBUSER} '{}' +
        echo "Permissions ok"
      else
        echo "Fast permissions check successful, if you have any permissions error try running with -e FORCE_PERMS_CHECK = true"
      fi
    fi

and then these mods to the stateful set podspec to patch it in:

      volumes:
        - name: script-permission-check-configmap
          configMap:
            name: lancache-script-permission-check
            defaultMode: 0777

        volumeMounts:
          - name: script-permission-check-configmap
            mountPath: /hooks/entrypoint-pre.d/20_perms_check.sh
            subPath: 20_perms_check.sh

It works as expected and I have not suffered any ill effects on a 1.5TB cache.

[VibroAxe]

LGTM @Lepidopterist ?

[VibroAxe]

LGTM

[Tyler-2]

Been running with this and still haven't discovered any problems.

[NelsonDane]

I've been using this patch for many months and wanted to confirm that it works well. Thank you @Tyler-2