Method write

src/os/Transaction.h:900–939

* Write data to an offset within an object. If the object is too * small, it is expanded as needed. It is possible to specify an * offset beyond the current end of an object and it will be * expanded as needed. Simple implementations of ObjectStore will * just zero the data between the old end of the object and the * newly provided data. More sophisticated implementations of * O

   * Note that a 0-length write does not affect the size of the object.
   */
  void write(const coll_t& cid, const ghobject_t& oid, uint64_t off, uint64_t len,
	       const ceph::buffer::list& write_data, uint32_t flags = 0) {
    using ceph::encode;
    Op* _op = _get_next_op();
    uint64_t alignstart = (0 - off) & ~CEPH_PAGE_MASK;
    _op->op = OP_WRITE;
    _op->cid = _get_coll_id(cid);
    _op->oid = _get_object_id(oid);
    _op->off = off;
    _op->len = len;
    ceph_assert(len == write_data.length());
    data.fadvise_flags = data.fadvise_flags | flags;
    data.ops = data.ops + 1;
    if (!is_format_aligned()) {
      encode(write_data, data_misaligned_bl);
      return;
    }
    if (len >= CEPH_PAGE_SIZE + alignstart) {
      uint64_t alignlen = (len - alignstart) & CEPH_PAGE_MASK;
      uint64_t suffixstart = alignstart + alignlen;
      if (alignstart != 0) {
        // Misaligned chunk at start
        bufferlist prefix;
        prefix.substr_of(write_data, 0, alignstart);
        encode_nohead(prefix, data_misaligned_bl);
      }
      // Aligned chunk in middle
      bufferlist aligned;
      aligned.substr_of(write_data, alignstart, alignlen);
      encode_nohead(aligned, data_aligned_bl);
      if (suffixstart != len) {
        // Misaligned chunk at end
        bufferlist suffix;
        suffix.substr_of(write_data, suffixstart, len-suffixstart);
        encode_nohead(suffix, data_misaligned_bl);
      }
    } else {
      encode_nohead(write_data, data_misaligned_bl);
    }
  }
  /**
   * zero out the indicated byte range within an object. Some
   * ObjectStore instances may optimize this to release the