Method decode_extra

src/client/FSCrypt.h:238–240

  uint8_t nonce[FSCRYPT_FILE_NONCE_SIZE];

  void decode_extra(bufferlist::const_iterator& bl) override {
    bl.copy(sizeof(nonce), (char *)nonce);
  }

  void encode_extra(bufferlist& bl) const override {
    bl.append((char *)nonce, sizeof(nonce));