about memory alignment

[Liuhao <liu.haoA@xxxxxxx>]

HI, developers:

data.largest_data_off_in_data_bl = orig_len + sizeof(__u32);  // we are about to
What 's mean of sizeof(__u32)?  Why add sizeof(__u32)?

Detail:
oid write(const coll_t& cid, const ghobject_t& oid, uint64_t off, uint64_t len,
                const bufferlist& write_data, uint32_t flags = 0) {
      uint32_t orig_len = data_bl.length();
      Op* _op = _get_next_op();
      _op->op = OP_WRITE;
      _op->cid = _get_coll_id(cid);
      _op->oid = _get_object_id(oid);
      _op->off = off;
      _op->len = len;
      ::encode(write_data, data_bl);

      assert(len == write_data.length());
      data.fadvise_flags = data.fadvise_flags | flags;
      if (write_data.length() > data.largest_data_len) {
         data.largest_data_len = write_data.length();
         data.largest_data_off = off;
         data.largest_data_off_in_data_bl = orig_len + sizeof(__u32);  // we are about to
      }
      data.ops++;
}

Thanks
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