class-design.cc

template <typename ImageCtxT>
class ParentWriteLog {
  //will contain all the common code between SSDWriteLog and ReplicatedWriteLog classes
};

template <typename ImageCtxT>
class SSDWriteLog : public ParentWriteLog<ImageCtxT> {
public:
  //SSD specific code
};

template <typename ImageCtxT>
class ReplicatedWriteLog : public ParentWriteLog<ImageCtxT> {
public:
  //RWL or AEP specific code
};

template <typename ImageCtxT>
class WriteLogCache : public ImageCache<ImageCtxT> {
  WriteLogCache::WriteLogCache() {
    ParentWriteLog *obj = new ReplicatedWriteLog (OR) new SSDWriteLog //depending on build or config options
  }
public:
  //will give access to client AIO methods like:
  void aio_read(Extents&& image_extents, ceph::bufferlist *bl,
                int fadvise_flags, Context *on_finish) override;
}

//existing classes like Request (librbd/cache/rwl/Request) will be able to work with ParentWriteLog type
//as the class is templated like below and where necessary we can do template specialization

template <typename T>
class C_BlockIORequest : public Context {
public:
  T &rwl; // This T currently is used with ReplicatedWriteLog
};