请问我这个最简单的StartIO为何只能被一次Write请求调用？

[njuliao]

#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？

[downbj]

你在派遣函数中把IRP加入队列的前调用IoMarkIrpPending