RBD中回調函數的變遷

rbd中涉及的回調，以寫入爲例，跟蹤回調函數的變遷。

@rbd.cc 
################################################           ******AioExportContext  && librbd::RBD::AioCompletion
 AioExportContext(SimpleThrottle &simple_throttle, librbd::Image &image,
                   uint64_t offset, uint64_t length, int fd)
    : m_aio_completion(
        new librbd::RBD::AioCompletion(this, &AioExportContext::aio_callback)), //this==AioExportContext AioExportContext::aio_callback
      m_throttle(simple_throttle),
      m_offset(offset),
      m_fd(fd)
  {
    m_throttle.start_op();

    int op_flags = LIBRADOS_OP_FLAG_FADVISE_SEQUENTIAL |
                   LIBRADOS_OP_FLAG_FADVISE_NOCACHE;
    int r = image.aio_read2(offset, length, m_bufferlist, m_aio_completion,                                                                                                                                       
                            op_flags);
    if (r < 0) { 
      cerr << "rbd: error requesting read from source image" << std::endl;
      m_throttle.end_op(r);
    }  
  }

 @librbd/librbd.cc  
#######################################               ******librbd::AioCompletion
  RBD::AioCompletion::AioCompletion(void *cb_arg, callback_t complete_cb)                                                                                                                                         
  {
    librbd::AioCompletion *c = librbd::aio_create_completion(cb_arg,               //cb_arg == AioExportContext complete_cb == AioExportContext::aio_callback
                                                             complete_cb);
    pc = (void *)c; 
    c->rbd_comp = this;
  }

 @librbd/internal.cc
 ####################################################
   AioCompletion *aio_create_completion(void *cb_arg, callback_t cb_complete) { 
    AioCompletion *c = new AioCompletion();
    c->set_complete_cb(cb_arg, cb_complete);          //cb_arg == AioExportContext complete_cb == AioExportContext::aio_callback 
    return c;                                                                                                                                                                                                     
  }

 @librbd/AioCompletion.h
 ######################################################
   struct AioCompletion {
  ¦ Mutex lock;                                                                                                                                                                                                   
  ¦ Cond cond;
  ¦ bool done;
  ¦ ssize_t rval;
  ¦ callback_t complete_cb;
  ¦ void *complete_arg;
  ¦ rbd_completion_t rbd_comp;
  ¦ int pending_count;   ///< number of requests
  ¦ uint32_t blockers;
  ¦ int ref;
  ¦ bool released;
  ¦ ImageCtx *ictx;
  ¦ utime_t start_time;
  ¦ aio_type_t aio_type;

  ¦ Striper::StripedReadResult destriper;
  ¦ bufferlist *read_bl;
  ¦ char *read_buf;
  ¦ size_t read_buf_len;

  ¦ AsyncOperation async_op;

  ¦ AioCompletion() : lock("AioCompletion::lock", true, false),
                ¦ ¦ ¦ done(false), rval(0), complete_cb(NULL),
                ¦ ¦ ¦ complete_arg(NULL), rbd_comp(NULL),
                ¦ ¦ ¦ pending_count(0), blockers(1),
                ¦ ¦ ¦ ref(1), released(false), ictx(NULL),
                ¦ ¦ ¦ aio_type(AIO_TYPE_NONE),
                ¦ ¦ ¦ read_bl(NULL), read_buf(NULL), read_buf_len(0) {
  ¦ }
  ...
  }

¦ void set_complete_cb(void *cb_arg, callback_t cb) {
¦ complete_cb = cb;   // cb == AioExportContext cb_arg == AioExportContext::aio_callback 
¦ complete_arg = cb_arg;
}

@librbd/internal.cc  aio_read()
#########################################          *******C_AioRead
C_AioRead *req_comp = new C_AioRead(ictx->cct, c)    //librbd::AioCompletion

AioRead *req = new AioRead(ictx, q->oid.name, q->objectno, q->offset,q->length, q->buffer_extents, snap_id, true,req_comp, op_flags) //req_comp == C_AioRead

@librbd/AioRequest.cc
##########################################      *********  librados::AioCompletion  
librados::AioCompletion *rados_completion = librados::Rados::aio_create_completion(this, rados_req_cb, NULL)  //this == AioRead rados_req_cb==rados_req_cb(librbd/internal.h)

librados::AioCompletion *librados::Rados::aio_create_completion(void *cb_arg,
                                                                callback_t cb_complete,
                                                                callback_t cb_safe)
{
  AioCompletionImpl *c;
  int r = rados_aio_create_completion(cb_arg, cb_complete, cb_safe, (void**)&c);                                                                                                                                  
  assert(r == 0);
  return new AioCompletion(c);
}



@/librados/librados.cc
#######################################################
int r = rados_aio_create_completion(cb_arg, cb_complete, cb_safe, (void**)&c) //cb_arg == AioRead cb_complete==rados_req_cb(librbd/internal.h)



@librados/librados.cc
#########################################################     ************* librados::AioCompletionImpl
extern "C" int rados_aio_create_completion(void *cb_arg,            //cb_arg == AioRead cb_complete==rados_req_cb(librbd/internal.h)
                                           rados_callback_t cb_complete,
                                           rados_callback_t cb_safe,
                                           rados_completion_t *pc) 
{
  tracepoint(librados, rados_aio_create_completion_enter, cb_arg, cb_complete, cb_safe);
  librados::AioCompletionImpl *c = new librados::AioCompletionImpl;
  if (cb_complete)
    c->set_complete_callback(cb_arg, cb_complete);
  if (cb_safe)
    c->set_safe_callback(cb_arg, cb_safe);
  *pc = c; 
  tracepoint(librados, rados_aio_create_completion_exit, 0, *pc);                                                                                                                                                 
  return 0;
}

總之在主邏輯進入不同的層級時都會伴隨着回調的變遷（封裝），最後他們的調用跟封裝過程是相反的。