请问我这个最简单的StartIO为何只能被一次Write请求调用？

2012-03-17 11:05:52 157 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

StartIO例程学习能够保证各个并行的IRP顺序执行，即串行化。很多时候，对设备的操作必须是串行化，驱动程序有必要将并行的请求变成串行的请求，需要用到队列。并行运行（函数执行交织在一起）如果想一次处理每个IRP，必须采用队列将处理串行化。采用“先来先服务”原则 typedef struct _KDEVICE_QUEUE { 阅读详情



#pragma LOCKED

void StartIO(IN PDEVICE_OBJECT pDevObj, IN PIRP pIrp)

{

	KdPrint(("Call StartIO\n"));

	KSPIN_LOCK a;

	KIRQL irql;

	KeAcquireSpinLock(&a, &irql);

	if(pIrp != pDevObj->CurrentIrp || pIrp->Cancel)

	{

		KeReleaseSpinLock(&a, irql);

		return;

	}

	else

	{

		IoSetCancelRoutine(pIrp, NULL);

		KeReleaseSpinLock(&a, irql);

	}

	

	PIO_STACK_LOCATION stack = IoGetCurrentIrpStackLocation(pIrp);



	int offset;

	int length;

	unsigned char key = stack->MajorFunction;

	pDevice_ext pdx = (pDevice_ext)pDevObj->DeviceExtension;



	if(key == IRP_MJ_READ)

	{

		offset = stack->Parameters.Read.ByteOffset.QuadPart;

		length = stack->Parameters.Read.Length;

		KdPrint(("Read %d %d\n", offset, length));

		if(offset + length <= pdx->datalen)

		{

			pIrp->IoStatus.Status = STATUS_SUCCESS;

			pIrp->IoStatus.Information = length;

			memcpy(pIrp->AssociatedIrp.SystemBuffer, pdx->data + offset, length);

		}

		else

		{

			pIrp->IoStatus.Status = STATUS_END_OF_FILE;

			pIrp->IoStatus.Information = 0;

		}

	}

	else if(key == IRP_MJ_WRITE)

	{

		offset = stack->Parameters.Write.ByteOffset.QuadPart;

		length = stack->Parameters.Write.Length;

		KdPrint(("Write %d %d\n", offset, length));

		if(offset + length <= pdx->datalen)

		{

			pIrp->IoStatus.Status = STATUS_SUCCESS;

			pIrp->IoStatus.Information = length;

			memcpy(pdx->data + offset, pIrp->AssociatedIrp.SystemBuffer, length);

		}

		else

		{

			pIrp->IoStatus.Status = STATUS_END_OF_FILE;

			pIrp->IoStatus.Information = 0;

		}

	}

	else

	{

		pIrp->IoStatus.Status = STATUS_NOT_IMPLEMENTED;

		pIrp->IoStatus.Information = 0;

	}

	



	KdPrint(("status = %d\n", pIrp->IoStatus.Status)); 

	IoCompleteRequest(pIrp, IO_NO_INCREMENT);

	IoStartNextPacket(pDevObj, true);

}

我设计一个用户进程，先后会调用两次异步的WriteFile
我的用户进程调用第一次WriteFile时，可以进入StartIO中并完成
调用第二次时，直接就没进入StartIO，一直就Pending着了。
我在IRP_MJ_WRITE的派遣函数中有这样子的句子:
KdPrint(("In io\n"));
IoStartPacket(pDevObj, pIrp, 0, OnCancelIRP);
KdPrint(("Out io\n"));
然后发现在调用IoStartPacket后，没进入StartIO函数
为什么？

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