Function crypt_keyslot_add_by_keyfile 

pub unsafe extern "C" fn crypt_keyslot_add_by_keyfile(
    cd: *mut crypt_device,
    keyslot: c_int,
    keyfile: *const c_char,
    keyfile_size: size_t,
    new_keyfile: *const c_char,
    new_keyfile_size: size_t,
) -> c_int