一个关于STATUS――PENDING的问题，请高手指点

请参考以下代码：

我的问题是：

  1。请问当请求发送当低级驱动后的执行流程是什么？（请以例子进行说明）
  2。当请求发送到低级驱动程序之后，当它返回STATUS_PENDING之后，完成例程要调用IoMarkIrpPending(Irp)，后面的KeSetEvent会不会被调用。如果KeSetEvent被调用，那么将使事件变为信号态，则将会杰出GpdDispatchPnp中的KeWaitForSingleObject的等待，按理STATUS_PENDING中线程应该在这个事件上等待呀，这样解除了有什么用呢？

NTSTATUS
GpdCompletionRoutine(
    IN PDEVICE_OBJECT   DeviceObject,
    IN PIRP             Irp,
    IN PVOID            Context
    )
/*++

Routine Description:

    The completion routine for plug & play irps that needs to be
    processed first by the lower drivers.

Arguments:

   DeviceObject - pointer to a device object.  

   Irp - pointer to an I/O Request Packet.

   Context - pointer to an event object.

Return Value:

      NT status code

--*/
{
    PKEVENT             event;

    event = (PKEVENT) Context;

    UNREFERENCED_PARAMETER(DeviceObject);

    if (Irp->PendingReturned) {
        IoMarkIrpPending(Irp);
    }

    //
    // We could switch on the major and minor functions of the IRP to perform
    // different functions, but we know that Context is an event that needs
    // to be set.
    //
    KeSetEvent(event, 0, FALSE);

    //
    // Allows the caller to reuse the IRP
    //
    return STATUS_MORE_PROCESSING_REQUIRED;
}


NTSTATUS
GpdDispatchPnp (
    IN PDEVICE_OBJECT DeviceObject,
    IN PIRP Irp
    )
/*++

Routine Description:

    The plug and play dispatch routines.

    Most of these the driver will completely ignore.
    In all cases it must pass the IRP to the next lower driver.

Arguments:

   DeviceObject - pointer to a device object.

   Irp - pointer to an I/O Request Packet.

Return Value:

      NT status code

--*/
{
    PIO_STACK_LOCATION          irpStack;
    NTSTATUS                    status = STATUS_SUCCESS;
    KEVENT                      event;        
    UNICODE_STRING              win32DeviceName;
    PLOCAL_DEVICE_INFO          deviceInfo;
 
    PAGED_CODE();

    deviceInfo = (PLOCAL_DEVICE_INFO) DeviceObject->DeviceExtension;
    irpStack = IoGetCurrentIrpStackLocation(Irp);

    status = IoAcquireRemoveLock (&deviceInfo->RemoveLock, NULL);
    if (!NT_SUCCESS (status)) {
        Irp->IoStatus.Status = status;
        IoCompleteRequest (Irp, IO_NO_INCREMENT);
        return status;
    }

    DebugPrint(("%s\n",PnPMinorFunctionString(irpStack->MinorFunction)));

    switch (irpStack->MinorFunction) {
    case IRP_MN_START_DEVICE:

        //
        // The device is starting.
        //
        // We cannot touch the device (send it any non pnp irps) until a
        // start device has been passed down to the lower drivers.
        //
        IoCopyCurrentIrpStackLocationToNext(Irp);
        KeInitializeEvent(&event,
                          NotificationEvent,
                          FALSE
                          );

        IoSetCompletionRoutine(Irp,
                               (PIO_COMPLETION_ROUTINE) GpdCompletionRoutine,
                               &event,
                               TRUE,
                               TRUE,
                               TRUE);
                              
        status = IoCallDriver(deviceInfo->NextLowerDriver, Irp);

        if (STATUS_PENDING == status) {
            KeWaitForSingleObject(
               &event,
               Executive, // Waiting for reason of a driver
               KernelMode, // Must be kernelmode if event memory is in stack
               FALSE, // No allert
               NULL); // No timeout
        }

        if (NT_SUCCESS(status) && NT_SUCCESS(Irp->IoStatus.Status)) {

            status = GpdStartDevice(DeviceObject, Irp);
            if(NT_SUCCESS(status))
            {
                //
                // As we are successfully now back from our start device
                // we can do work.
                //
                
                deviceInfo->Started = TRUE;
                deviceInfo->Removed = FALSE;
            }
        }

        //
        // We must now complete the IRP, since we stopped it in the
        // completion routine with STATUS_MORE_PROCESSING_REQUIRED.
        //
        Irp->IoStatus.Status = status;
        IoCompleteRequest(Irp, IO_NO_INCREMENT);
        break;

  

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