Function hard_link 

pub async fn hard_link<P, Q>(src: P, dst: Q) -> Result<()>
where
    P: AsRef<Path>,
    Q: AsRef<Path>,

Makes dst another name for the file src.

Runs std::fs::hard_link on the thread that polls the future. Both names refer to the same file. Most operating systems allow this only for two names on the same filesystem.