派遣函数学习3）其他方式读写设备

首先    既不设置 DO_DIRECT_IO /  DO_BUFFER_IO

派遣函数直接读写应用程序提供的缓冲区地址。  直接操应用程序的缓冲区地址是很危险的

只有驱动程序与应用程序运行再相同线程上下文的时候，才能用这种方式

探测可读可写用： ProbeForWrite   +   try 块

NTSTATUS HelloDDKRead(IN PDEVICE_OBJECT pDevObj,
								 IN PIRP pIrp) 
{
	KdPrint(("Enter HelloDDKRead
"));

	PDEVICE_EXTENSION pDevExt = (PDEVICE_EXTENSION)pDevObj->DeviceExtension;
	NTSTATUS status = STATUS_SUCCESS;

	//得到当前堆栈
	PIO_STACK_LOCATION stack = IoGetCurrentIrpStackLocation(pIrp);
	//得到读的长度
	ULONG ulReadLength = stack->Parameters.Read.Length;
	//得到读的偏移量
	ULONG ulReadOffset = (ULONG)stack->Parameters.Read.ByteOffset.QuadPart;
	//得到用户模式地址
	PVOID user_address = pIrp->UserBuffer;

	KdPrint(("user_address:0X%0X
",user_address));

	__try
	{
		KdPrint(("Enter __try block
"));
		//判断空指针是否可写，显然会导致异常
		ProbeForWrite(user_address,ulReadLength,4);

		memset(user_address,0xAA,ulReadLength);

		//由于在上面引发异常，所以以后语句不会被执行!
		KdPrint(("Leave __try block
"));
	}
	__except(EXCEPTION_EXECUTE_HANDLER)
	{
		KdPrint(("Catch the exception
"));
		KdPrint(("The program will keep going
"));
		status = STATUS_UNSUCCESSFUL;
	}

	pIrp->IoStatus.Status = status;
	pIrp->IoStatus.Information = ulReadLength;	// bytes xfered
	IoCompleteRequest( pIrp, IO_NO_INCREMENT );
	KdPrint(("Leave HelloDDKRead
"));

	return status;
}