nfs: make DeleteVolume (more) idempotent

Signed-off-by: Niels de Vos <ndevos@redhat.com>

internal/nfs/controller/errors.go

@@ -0,0 +1,43 @@
+/*
+Copyright 2022 The Ceph-CSI Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package controller
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	// ErrNotConnected is returned when components from the NFS
+	// ControllerServer can not connect to the Ceph cluster or NFS-Ganesha
+	// service.
+	ErrNotConnected = errors.New("not connected")
+
+	// ErrNotFound is a generic error that is the parent of other "not
+	// found" failures. Callers can check if something was "not found",
+	// even if the actual error is more specific.
+	ErrNotFound = errors.New("not found")
+
+	// ErrExportNotFound is returned by components that communicate with the
+	// NFS-Ganesha service, and have identified that the NFS-Export does
+	// not exist (anymore). This error is also a ErrNotFound.
+	ErrExportNotFound = fmt.Errorf("NFS-export %w", ErrNotFound)
+
+	// ErrFilesystemNotFound is returned in case the filesystem
+	// does not exist.
+	ErrFilesystemNotFound = fmt.Errorf("filesystem %w", ErrNotFound)
+)