急求讲授张帆《Windows驱动开发技术详解》的虚拟串口驱动，求讲解

急!求讲解张帆《Windows驱动开发技术详解》的虚拟串口驱动，求讲解
第19章，虚拟串口驱动，求讲解。有意的加我qq:545039712.我出钱。
需要讲解的代码如下：
NTSTATUS HelloWDMRead(IN PDEVICE_OBJECT fdo,
                        IN PIRP Irp)
{
KdPrint(("HelloWDMRead\n"));

    NTSTATUS ntStatus = STATUS_SUCCESS;// Assume success

PDEVICE_EXTENSION pExtension = (PDEVICE_EXTENSION)fdo->DeviceExtension;

    PIO_STACK_LOCATION irpSp = IoGetCurrentIrpStackLocation( Irp );

ULONG BufLen = irpSp->Parameters.Read.Length;
PCHAR pBuf = (PCHAR)Irp->AssociatedIrp.SystemBuffer;

    KIRQL OldIrql;

    PDRIVER_CANCEL pOldCancelRoutine;

Irp->IoStatus.Information = 0;

DbgPrint("DeviceObject:%08X Read\n",fdo);

if (BufLen == 0)
    {
ntStatus = STATUS_SUCCESS;
    }
else
{
        KeAcquireSpinLock(&pExtension->WriteSpinLock, &OldIrql);

RtlCopyMemory(pBuf,pExtension->Buffer,BufLen);

Irp->IoStatus.Information = BufLen;

if (BufLen==0 && pExtension->pReadIrp==NULL) // nothing, store
{
pExtension->pReadIrp = Irp;
Irp->IoStatus.Status = ntStatus = STATUS_PENDING;

            IoSetCancelRoutine(Irp, DriverCancelCurrentReadIrp);

            if (Irp->Cancel)
            {
                pOldCancelRoutine = IoSetCancelRoutine(Irp, NULL);

                if (pOldCancelRoutine != NULL)
                {
                    // Nein, also IRP hier abbrechen
                    Irp->IoStatus.Status = ntStatus = STATUS_CANCELLED;

                    pExtension->pReadIrp = NULL;
                }
                else
                {
                    // Ja, Cancel-Routine wird Request beenden
                    IoMarkIrpPending(Irp);
                }
}
else
{
                    IoMarkIrpPending(Irp);
}
}

        KeReleaseSpinLock(&pExtension->WriteSpinLock, OldIrql);

}

    Irp->IoStatus.Status = ntStatus;
if (ntStatus != STATUS_PENDING)
IoCompleteRequest( Irp, IO_NO_INCREMENT );

    return ntStatus;
}

NTSTATUS HelloWDMWrite(IN PDEVICE_OBJECT fdo,
                        IN PIRP Irp)
{
KdPrint(("HelloWDMWrite\n"));

    NTSTATUS ntStatus = STATUS_SUCCESS;// Assume success

PDEVICE_EXTENSION pdx = (PDEVICE_EXTENSION)fdo->DeviceExtension;

    PIO_STACK_LOCATION irpSp = IoGetCurrentIrpStackLocation( Irp );

ULONG DataLen = irpSp->Parameters.Write.Length;

PUCHAR pData = (PUCHAR)Irp->AssociatedIrp.SystemBuffer;

    KIRQL OldIrql;

    PIRP            pOldReadIrp = NULL;
    PDRIVER_CANCEL  pOldCancelRoutine;

Irp->IoStatus.Information = 0;
ntStatus = STATUS_SUCCESS;

if (DataLen == 0)
    {
ntStatus = STATUS_SUCCESS;
    }else if (DataLen>COMBUFLEN)
    {
ntStatus = STATUS_INVALID_PARAMETER;
    }
else
{
KdPrint(("Write\n"));
        
KeAcquireSpinLock(&pdx->WriteSpinLock, &OldIrql);