//清理缓冲  《寒江独钓》p233
void cfFileCacheClear(PFILE_OBJECT pFileObject)
{
   PFSRTL_COMMON_FCB_HEADER pFcb;
   LARGE_INTEGER liInterval;
   BOOLEAN bNeedReleaseResource = FALSE;
   BOOLEAN bNeedReleasePagingIoResource = FALSE;
   KIRQL irql;

   pFcb = (PFSRTL_COMMON_FCB_HEADER)pFileObject->FsContext;	//从文件对象得到FCB(file control block 文件控制块)
   if(pFcb == NULL)
       return;

   irql = KeGetCurrentIrql();	//得到当前IRQL并保证不大于DISPATCH_LEVEL方可进行
   if (irql >= DISPATCH_LEVEL)	//其后函数需要在小于DISPATCH_LEVEL级别上执行
   {
       return;
   }

   liInterval.QuadPart = -1 * (LONGLONG)50;	//后面需使用的等待时间

   while (TRUE)
   {
       BOOLEAN bBreak = TRUE;
       BOOLEAN bLockedResource = FALSE;
       BOOLEAN bLockedPagingIoResource = FALSE;
       bNeedReleaseResource = FALSE;
       bNeedReleasePagingIoResource = FALSE;

	   // 到fcb中去拿锁。
       //测试当前线程是否有指定资源的独占访问权。返回TRUE
	   if (pFcb->PagingIoResource)
           bLockedPagingIoResource = ExIsResourceAcquiredExclusiveLite(pFcb->PagingIoResource);



	   // 总之一定要拿到这个锁。
       if (pFcb->Resource)		
       {
           bLockedResource = TRUE;
           if (ExIsResourceAcquiredExclusiveLite(pFcb->Resource) == FALSE)	
			   //此处不解？？为什么要不能互斥获得pFcb->Resource才开始以下处理？
           {
               bNeedReleaseResource = TRUE;	//开始获得资源 并将标识置为真。为其后不能同时获得RESOURCE及PAGERESURCE做释放准备
											//不能全部获得两设备必须释放并重新进行获取过程，直到全部获取两资源。


               if (bLockedPagingIoResource)	//此处不解？？根据另一资源能否互斥获取来决定获得本资源时等待还是立即返回？
               {
                   if (ExAcquireResourceExclusiveLite(pFcb->Resource, FALSE) == FALSE)
                   {
                       bBreak = FALSE;		//获取失败自然BREAK标记为FALSE，继续循环
                       bNeedReleaseResource = FALSE;	//获取失败，
                       bLockedResource = FALSE;
                   }
               }
               else					//有独占访问权则互斥获得资源
                   ExAcquireResourceExclusiveLite(pFcb->Resource, TRUE);
           }
       }
	   
       if (bLockedPagingIoResource == FALSE)		//获取PAGINGIORESOURCE类似获取RESOURCE
       {
           if (pFcb->PagingIoResource)
           {
               bLockedPagingIoResource = TRUE;
               bNeedReleasePagingIoResource = TRUE;
               if (bLockedResource)
               {
                   if (ExAcquireResourceExclusiveLite(pFcb->PagingIoResource, FALSE) == FALSE)
                   {
                       bBreak = FALSE;
                       bLockedPagingIoResource = FALSE;
                       bNeedReleasePagingIoResource = FALSE;
                   }
               }
               else
               {
                   ExAcquireResourceExclusiveLite(pFcb->PagingIoResource, TRUE);
               }
           }
       }
	   
       if (bBreak)		
       {
           break;
       }
       

	   //只获得其中一个资源必须释放，防止死锁。等待指定时间后，继续获取
       if (bNeedReleasePagingIoResource)
       {
           ExReleaseResourceLite(pFcb->PagingIoResource);
       }
       if (bNeedReleaseResource)
       {
           ExReleaseResourceLite(pFcb->Resource);		
       }
	   
       if (irql == PASSIVE_LEVEL)				//等待指定时间后继续循环
       {
           KeDelayExecutionThread(KernelMode, FALSE, &liInterval);
		   //KeDelayExecutionThread must be running at IRQL = PASSIVE_LEVEL.
       }
       else
       {
		   //其他IRQL等级下 使用这种方法等待
           KEVENT waitEvent;
           KeInitializeEvent(&waitEvent, NotificationEvent, FALSE);
           KeWaitForSingleObject(&waitEvent, Executive, KernelMode, FALSE, &liInterval);
       }
   }
   


//互斥获取资源均为刷新缓存做准备。
   if (pFileObject->SectionObjectPointer)
   {
	   IO_STATUS_BLOCK ioStatus;
	   CcFlushCache(pFileObject->SectionObjectPointer, NULL, 0, &ioStatus);
	   if (pFileObject->SectionObjectPointer->ImageSectionObject)
	   {
		   MmFlushImageSection(pFileObject->SectionObjectPointer,MmFlushForWrite); // MmFlushForDelete
	   }
	   CcPurgeCacheSection(pFileObject->SectionObjectPointer, NULL, 0, FALSE);
   }
   
   if (bNeedReleasePagingIoResource)
   {
       ExReleaseResourceLite(pFcb->PagingIoResource);
   }
   if (bNeedReleaseResource)
   {
       ExReleaseResourceLite(pFcb->Resource);
   }
}

[招生]科锐逆向工程师培训(2024年11月15日实地，远程教学同时开班, 第51期)