Function change 

pub fn change(
    path: &Path,
    vault: Option<(&Path, &[u8; 32])>,
    change: impl FnOnce(&mut Entry),
) -> Result<Entry, String>

This device’s own entry changed by change, under its lock, read just before: written here, then, sharing on (vault: the folder and its key), into the folder when the others need it (see the module’s words). Returns it as written here.