message: Fix bug in mem_fs: parent of foo.txt is root dir
diff: @@ -327,7 +327,7 @@ impl FileSystemInner {
  let mut components = path.components();
  match components.next() {
  - Some(Component::RootDir) => {}
  + Some(Component::RootDir) | None => {}
  _ => return Err(FsError::BaseNotDirectory),
  }
  