Improve fs package and doc in prep to officially go public

pkg/fs/fileinfo.go

@@ -0,0 +1,34 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package fs
+
+import (
+	"os"
+	"time"
+)
+
+var _ os.FileInfo = &fileInfo{}
+
+// fileInfo implements os.FileInfo for a fileInMemory instance.
+type fileInfo struct {
+	*fileInMemory
+}
+
+// Name returns the name of the file
+func (fi *fileInfo) Name() string { return fi.name }
+
+// Size returns the size of the file
+func (fi *fileInfo) Size() int64 { return int64(len(fi.content)) }
+
+// Mode returns the file mode
+func (fi *fileInfo) Mode() os.FileMode { return 0777 }
+
+// ModTime returns the modification time
+func (fi *fileInfo) ModTime() time.Time { return time.Time{} }
+
+// IsDir returns if it is a directory
+func (fi *fileInfo) IsDir() bool { return fi.dir }
+
+// Sys should return underlying data source, but it now returns nil
+func (fi *fileInfo) Sys() interface{} { return nil }