CacheControlRequest代码分析

谁能帮我分析这断代码？ 刚开始写Driver的。 10分
NTSTATUS CacheControlRequest(PDEVICE_EXTENSION pdx, PIRP Irp, PIRP* pIrp)
{
ASSERT(KeGetCurrentIrql() <= DISPATCH_LEVEL);

KIRQL oldirql;
KeAcquireSpinLock(&pdx->IoctlListLock, &oldirql);

NTSTATUS status;

if (*pIrp)
{
status = STATUS_UNSUCCESSFUL;                          // Something already cached here
}
else if (pdx->IoctlAbortStatus)
{
status = pdx->IoctlAbortStatus;                   // Rejecting new IRPs for some reason
}
else
{                                                   // Try to cache IRP
IoSetCancelRoutine(Irp, OnCancelPendingIoctl);
if (Irp->Cancel && IoSetCancelRoutine(Irp, NULL))
{
status = STATUS_CANCELLED;                      // Already cancelled
}
else
{                                                 // If to cache it
IoMarkIrpPending(Irp);
status = STATUS_PENDING;

PIO_STACK_LOCATION stack = IoGetCurrentIrpStackLocation(Irp);
stack->Parameters.Others.Argument1 = (PVOID) pIrp;
IoSetCompletionRoutine(Irp, (PIO_COMPLETION_ROUTINE) OnCompletePendingIoctl, (PVOID) pdx, TRUE, TRUE, TRUE);

IoSetNextIrpStackLocation(Irp);                 // So our completion routine will get called
PFILE_OBJECT fop = stack->FileObject;
stack = IoGetCurrentIrpStackLocation(Irp);
stack->DeviceObject = pdx->DeviceObject;        // So IoCancelIrp can give us right ptr
stack->FileObject   = fop;                      // For cleanup

*pIrp = Irp;
InsertTailList(&pdx->PendingIoctlList, &Irp->Tail.Overlay.ListEntry);
}
}

KeReleaseSpinLock(&pdx->IoctlListLock, oldirql);
return status;
}

分析个什么？？？？？？？？？？？？？？？？？？？？？？？？？