let BLS_ENTRIES = "/some/prefix/";
let entry = String::new("../../../some/prefix/foobar.conf");
let path = std::path::Path::new(&entry);
let abs_path = path.canonicalize();

// We try to ensure that the path exists, that it's a file in BLS_ENTRIES and that it's suffix is .conf
match abs_path {
  Ok(abs_path) => {
    if abs_path.exists() {
      if abs_path.parent() != Some(Path::new(BLS_ENTRIES)) {
        return Err(format!("entry argument {} is not in bootloader entry directory {}", entry, BLS_ENTRIES));
      }
      if !abs_path.ends_with(".conf") {
        return Err(format!("entry argument {:?} does not have .conf suffix", abs_path));
      }
      match abs_path.file_stem() {
        Some(file_stem) => {
          match file_stem.to_str() {
            Some(file_stem) => {
              return Ok(BLSEntry::new(String::from(file_stem)));
            }
            _ => {}
          }
        }
        _ => {}
      }
    }
  },
  _ => {}
}