DefaultSync task syncs the image meta data and layer data to remote dir.

DirStructureSync build the dir structure for the remote dir.

LockRequest locks acquire the central lock.

NodeRegisterResponse set a NodeID for every syncd node at present.

TaskRegisterRequest send by syncd to register a sync tack.

TaskRegisterResponse represents the register response.

TaskStatusRequest send by syncd to request the status of a task.

TaskStatusResponse represents the task status response.