Function crypt_keyslot_add_by_key 

pub unsafe extern "C" fn crypt_keyslot_add_by_key(
    cd: *mut crypt_device,
    keyslot: c_int,
    volume_key: *const c_char,
    volume_key_size: size_t,
    passphrase: *const c_char,
    passphrase_size: size_t,
    flags: u32,
) -> c_int