这个例程序大概讲了什么功能?

NTSTATUS DispatchReadWrite (
IN PDEVICE_OBJECT pDevObj,
IN PIRP pIrp ) {
#if DBG>=1
DbgPrint(\"THREADDMA: Read/Write Operation requested (DispatchWrite)\\n\");
#endif

PIO_STACK_LOCATION pIrpStack =
IoGetCurrentIrpStackLocation( pIrp );

PDEVICE_EXTENSION pDE = (PDEVICE_EXTENSION)
pDevObj->DeviceExtension;

// Check for zero-length transfers
if ( pIrpStack->Parameters.Read.Length == 0 )  {
pIrp->IoStatus.Status = STATUS_SUCCESS;
pIrp->IoStatus.Information = 0;
IoCompleteRequest( pIrp, IO_NO_INCREMENT );
return STATUS_SUCCESS;
}

// Start device operation
IoMarkIrpPending( pIrp );

// Add the IRP to the thread\'s work queue
ExInterlockedInsertTailList (
&pDE->IrpQueueListHead,
&pIrp->Tail.Overlay.ListEntry,
&pDE->lkIrpQueue );

KeReleaseSemaphore(
&pDE->semIrpQueue,
0, // No priority boost
1, // Increment semaphore by 1
FALSE ); // No WaitForXxx after this call

return STATUS_PENDING;
}