Implement support for calculating disk usage per tenant (#5969)

Fixes #5961

cmd/disk-usage.go

@@ -0,0 +1,59 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * 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 cmd
+
+import (
+	"context"
+	"time"
+)
+
+const (
+	usageCheckInterval = 12 * time.Hour // 12 hours
+)
+
+// getDiskUsage walks the file tree rooted at root, calling usageFn
+// for each file or directory in the tree, including root.
+func getDiskUsage(ctx context.Context, root string, usageFn usageFunc) error {
+	return walk(ctx, root+slashSeparator, usageFn)
+}
+
+type usageFunc func(ctx context.Context, entry string) error
+
+// walk recursively descends path, calling walkFn.
+func walk(ctx context.Context, path string, usageFn usageFunc) error {
+	if err := usageFn(ctx, path); err != nil {
+		return err
+	}
+
+	if !hasSuffix(path, slashSeparator) {
+		return nil
+	}
+
+	entries, err := readDir(path)
+	if err != nil {
+		return usageFn(ctx, path)
+	}
+
+	for _, entry := range entries {
+		fname := pathJoin(path, entry)
+		if err = walk(ctx, fname, usageFn); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}