在系统线程里直接向USBD发请求来和设备读取数据。如何做呢。给个思路吧

那位大侠能讲解USB驱动中构建一个URB并传到USBD所要的主要函数和流程呢。中间是要通过IRP来传的。
我现在想在系统线程里直接向USBD发请求来和设备读取数据。如何做呢。给个思路吧
  

怎么没人给点意见呢。是不是我问的问题太菜，或不解其意啊。




不在郁闷中成长，就在郁闷中毁灭。

我的源码想这样：
我在系统线程中调用下面的函数；
void ThreadProc(PDEVICE_EXTENSION pdx )
{
  while(true)
{
  Ezusb_Read_Write(usbfdo,usbIrp);//
     就在这句，我不知道如何把上面这个函数所要的环境传进去，我就用了全局变量usbfdo,usbIrp.在我DeviceIoControl的时候就把fdo,irp 赋值给usbfdo,usbIrp.但在函数里面语句 PIO_STACK_LOCATION irpStack = IoGetCurrentIrpStackLocation (Irp);
PBULK_TRANSFER_CONTROL bulkControl =
(PBULK_TRANSFER_CONTROL)Irp->AssociatedIrp.SystemBuffer;这里bulkControl的值传不进来。我想是IoGetCurrentIrpStackLocation 的关系吧。
？？？？
  IoGetCurrentIrpStackLocation这个函数要如何使用，在什么环境下用呢。
？？？？
//
}

}
NTSTATUS
Ezusb_Read_Write(
IN PDEVICE_OBJECT fdo,
IN PIRP Irp
)
/*++
Routine Description:

Arguments:

Return Value:
NT status code
STATUS_SUCCESS: Read was done successfully
STATUS_INVALID_PARAMETER_3: The Endpoint Index does not specify an IN pipe
STATUS_NO_MEMORY: Insufficient data memory was supplied to perform the READ

This routine fills the status code into the Irp

--*/
{
PDEVICE_EXTENSION pdx = fdo->DeviceExtension;
NTSTATUS ntStatus;
PIO_STACK_LOCATION irpStack = IoGetCurrentIrpStackLocation (Irp);
PBULK_TRANSFER_CONTROL bulkControl =
(PBULK_TRANSFER_CONTROL)Irp->AssociatedIrp.SystemBuffer;
ULONG bufferLength =
irpStack->Parameters.DeviceIoControl.OutputBufferLength;
PURB urb = NULL;
ULONG urbSize = 0;
ULONG transferFlags = 0;
PUSBD_INTERFACE_INFORMATION interfaceInfo = NULL;
PUSBD_PIPE_INFORMATION pipeInfo = NULL;
USBD_PIPE_HANDLE pipeHandle = NULL;


Ezusb_KdPrint((\"enter Ezusb_Read_Write()n\"));

//
// verify that the selected pipe is valid, and get a handle to it. If anything
// is wrong, return an error
//
interfaceInfo = pdx->Interface;

if (!interfaceInfo)
{
Ezusb_KdPrint((\"Ezusb_Read_Write() no interface info - Exitingn\"));
return STATUS_UNSUCCESSFUL;
}

if (bulkControl->pipeNum > interfaceInfo->NumberOfPipes)
{
Ezusb_KdPrint((\"Ezusb_Read_Write() invalid pipe - Exitingn\"));
return STATUS_INVALID_PARAMETER;
}

pipeInfo = &(interfaceInfo->Pipes[bulkControl->pipeNum]);

if (!((pipeInfo->PipeType == UsbdPipeTypeBulk) ||
(pipeInfo->PipeType == UsbdPipeTypeInterrupt)))
{
Ezusb_KdPrint((\"Ezusb_Read_Write() invalid pipe - Exitingn\"));
return STATUS_INVALID_PARAMETER;
}

pipeHandle = pipeInfo->PipeHandle;

if (!pipeHandle)
{
Ezusb_KdPrint((\"Ezusb_Read_Write() invalid pipe - Exitingn\"));
return STATUS_UNSUCCESSFUL;
}

if (bufferLength > pipeInfo->MaximumTransferSize)
{
Ezusb_KdPrint((\"Ezusb_Read_Write() invalid transfer size - Exitingn\"));
return STATUS_INVALID_PARAMETER;
}

//
// allocate and fill in the Usb request (URB)
//
urbSize = sizeof(struct _URB_BULK_OR_INTERRUPT_TRANSFER);

urb = ExAllocatePool(NonPagedPool,urbSize);

if (!urb)
{
Ezusb_KdPrint((\"Ezusb_Read_Write() unable to alloc URB - Exitingn\"));
return STATUS_NO_MEMORY;
}


transferFlags = USBD_SHORT_TRANSFER_OK;

//
// get direction info from the endpoint address
//
if (USB_ENDPOINT_DIRECTION_IN(pipeInfo->EndpointAddress))
transferFlags |= USBD_TRANSFER_DIRECTION_IN;

UsbBuildInterruptOrBulkTransferRequest(urb, //ptr to urb
(USHORT) urbSize, //size of urb
pipeHandle, //usbd pipe handle
NULL, //TransferBuffer
Irp->MdlAddress, //mdl
bufferLength, //bufferlength
transferFlags, //flags
NULL); //link

//
// Call the USB Stack.

ntStatus = Ezusb_CallUSBD(fdo, urb);

//
// If the transfer was successful, report the length of the transfer to the
// caller by setting IoStatus.Information
//
if (NT_SUCCESS(ntStatus))
{
Irp->IoStatus.Information = urb->UrbBulkOrInterruptTransfer.TransferBufferLength;
Ezusb_KdPrint((\"Successfully transfered 0x%x bytesn\",Irp->IoStatus.Information));
}

//
// free the URB
//
ExFreePool(urb);

return ntStatus;
}