passthru中PtBindAdapter实现流程

本人刚接触passthru，谁能讲解一下passthru中PtBindAdapter实现流程啊？

NdisOpenProtocolConfiguration(Status,&ConfigHandle,SystemSpecific1);

NdisReadConfiguration(Status,&Param,ConfigHandle, &DeviceStr, NdisParameterString);

TotalSize = sizeof(ADAPT) + Param->ParameterData.StringData.MaximumLength;

 NdisAllocateMemoryWithTag(&pAdapt, TotalSize, TAG);

这几行代码在做什么啊？TotalSize的大小怎么计算的呢？