//Copy the packet into a buffer
  while (CurrentMdl && DataLength > 0)
    {
      NdisQueryMdl(CurrentMdl, &pSrc, &CurrLength, NormalPagePriority);
      if (pSrc == NULL)
        {
	  bytesCopied = 0;
	  break;
        }
        
      //
      //  Current buffer length is greater than the offset to the buffer
      //
      
      if (CurrLength > Offset)
        {
	  pSrc += Offset;
	  CurrLength -= Offset;
	  
	  if (CurrLength > DataLength)
            {
	      CurrLength = DataLength;
            }
	  DataLength -= CurrLength;
	  NdisMoveMemory(pDest, pSrc, CurrLength);
	  bytesCopied += CurrLength;
            
	  pDest += CurrLength;
	  Offset = 0;
        }
      else
        {
	  Offset -= CurrLength;
        }
      NdisGetNextMdl(CurrentMdl, &CurrentMdl);
      
    }
  

?

這段代碼就是拷貝數(shù)據(jù)到緩沖區(qū)。其中CurrMDL,offset和dataLength來(lái)自Net_Buffer:

    pNetBuffer = NET_BUFFER_LIST_FIRST_NB(pNetBufferList);
  
  //
  // Try to get the 1p data from OOB data
  //
  if(NET_BUFFER_LIST_INFO(pNetBufferList, Ieee8021QNetBufferListInfo) != 0)
    {
      Ndis8021QInfo.Value = NET_BUFFER_LIST_INFO(pNetBufferList, Ieee8021QNetBufferListInfo);
      UserPriority  = (UCHAR)Ndis8021QInfo.TagHeader.UserPriority;
    }     
  
  //copy the packet into a buffer
  pDest = packetBuffer;
  
  CurrentMdl = pNetBuffer->MdlChain;
  Offset = pNetBuffer->DataOffset;
  DataLength = pNetBuffer->DataLength;
  

?其中NET_BUFFER_LIST_FIRST_NB返回的是第一個(gè)Net_Buffer.? CurrentMDL指向MDL的list.現(xiàn)在來(lái)看看如何拷貝數(shù)據(jù)的。其中NdisQueryMdl返回MDL虛擬地址的基地址Psrc，和對(duì)應(yīng)的緩沖區(qū)長(zhǎng)度CurrLength


?
?1、如果CurrLenght >?offset,那么把Psrc+offset,指向used data.同樣，CurrLength-offset，表示當(dāng)前的MDL中有用的數(shù)據(jù)長(zhǎng)度。然后執(zhí)行NdisMoveMemory的拷貝操作.緊接著把，dataLength-CurrLength,因?yàn)橐呀?jīng)拷貝好了一部分，然后再把offset置零，因?yàn)楝F(xiàn)在指針已經(jīng)到了可用數(shù)據(jù)區(qū)。

2、當(dāng)再次得到下一個(gè)MDL的Psrc,和CurrLength時(shí)，因?yàn)閛ffset已經(jīng)=0，所以CurrLength肯定大于0，所以即使執(zhí)行PSrc+=offset, CurrLength-=offset.最后拷貝整個(gè)長(zhǎng)度的空間(以圖為例，不都是這樣！！)，dataLength-CurrLength.

3、最后第三次得到pSrc,和CurrLength,但是CurrLength,已經(jīng)大于dataLength，所以只拷貝dataLength的長(zhǎng)度數(shù)據(jù)。就完成了所有數(shù)據(jù)拷貝。

4、但是如果第一次的時(shí)候offset>CurrLength,那么就是比如圖中第一個(gè)MDL為unused data區(qū)，執(zhí)行offset-=CurrLength.如下圖：

?

?這樣之后又回到了前面所說(shuō)的CurrLength>offset了。

這就是拷貝數(shù)據(jù)到緩沖區(qū)的過(guò)程。不知有何疏漏，或者錯(cuò)誤，見(jiàn)諒~
?

拷貝MDL中數(shù)據(jù)到緩沖區(qū)