rbd: implement CSI-Addons ControllerReclaimSpace

The CSI Controller (provisioner) can call `rbd sparsify` to reduce the
space consumption of the volume.

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

internal/rbd/diskusage.go

@@ -0,0 +1,44 @@
+/*
+Copyright 2021 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 rbd
+
+import (
+	"fmt"
+)
+
+// Sparsify checks the size of the objects in the RBD image and calls
+// rbd_sparify() to free zero-filled blocks and reduce the storage consumption
+// of the image.
+func (ri *rbdImage) Sparsify() error {
+	image, err := ri.open()
+	if err != nil {
+		return err
+	}
+	defer image.Close()
+
+	imageInfo, err := image.Stat()
+	if err != nil {
+		return err
+	}
+
+	err = image.Sparsify(1 << imageInfo.Order)
+	if err != nil {
+		return fmt.Errorf("failed to sparsify image: %w", err)
+	}
+
+	return nil
+}