Function sample_files 

pub fn sample_files(
    files: &[PathBuf],
    format: FileFormat,
    as_read: &ReadAs,
) -> Sampled

Read a spread of files and say what they are.

The ends and the middle, because names sort and a directory written table by table can start with several files of the same table. Three reads whatever the directory’s size: this runs in a listing pass and on the way into an open, and a directory of forty thousand files must cost the same as a directory of four.