Method obtain_contiguous_space

src/common/buffer.cc:1383–1412

  }

  buffer::list::reserve_t buffer::list::obtain_contiguous_space(
    const unsigned len)
  {
    // note: if len < the normal append_buffer size it *might*
    // be better to allocate a normal-sized append_buffer and
    // use part of it.  however, that optimizes for the case of
    // old-style types including new-style types.  and in most
    // such cases, this won't be the very first thing encoded to
    // the list, so append_buffer will already be allocated.
    // OTOH if everything is new-style, we *should* allocate
    // only what we need and conserve memory.
    if (unlikely(get_append_buffer_unused_tail_length() < len)) {
      auto new_back = \
	buffer::ptr_node::create(buffer::create(len)).release();
      new_back->set_length(0);   // unused, so far.
      _buffers.push_back(*new_back);
      _num += 1;
      _carriage = new_back;
      return { new_back->c_str(), &new_back->_len, &_len };
    } else {
      ceph_assert(!_buffers.empty());
      if (unlikely(_carriage != &_buffers.back())) {
        auto bptr = ptr_node::create(*_carriage, _carriage->length(), 0);
	_carriage = bptr.get();
	_buffers.push_back(*bptr.release());
        _num += 1;
      }
      return { _carriage->end_c_str(), &_carriage->_len, &_len };
    }
  }

  void buffer::list::append(const ptr& bp)
  {