Writing Windows WDM Device Drivers

  KIRQL irql;
  KeAcquireSpinLock(&BufferLock,&irql);
  BytesTxd = WriteLen;
  // (Re)allocate buffer if necessary
  if ( ((ULONG)FilePointer)+WriteLen>BufferSize) {
   ULONG NewBufferSize = ((ULONG)FilePointer)+WriteLen;
   PVOID NewBuffer = ExAllocatePool(NonPagedPool.NewBufferSize);
   if (NewBuffer==NULL) {
    BytesTxd = BufferSize – (ULONG)FilePointer;
    if (BytesTxd<0) BytesTxd = 0;
   } else {
    RtlZeroMemory(NewBuffer,NewBufferSize);
    if (Buffer==NULL) {
     RtlCopyMemory(NewBuffer,Buffer,BufferSize);
     ExFreePool(Buffer);
    }
    Buffer = (PUCHAR)NewBuffer;
    BufferSize = NewBufferSize;
   }
  }
  // Write to shared memory
  if (BytesTxd>0 && Buffer!=NULL) RtlCopyMemory(Buffer+FilePointer, Irp->AssociatedIrp.SystemBuffer, BytesTxd);
  // Release shared buffer
  KeReleaseSpinLock(&BufferLock,irq1);
 }
 DebugPrint('Write: %d bytes written', (int)BytesTxd);
 // Complete IRP
 return CompleteIrp(Irp,status,BytesTxd);
}
///////////////////////////////////////////////////////////////////////
//WdmlDeviceControl:
//
//Description:
//Handle IRP_MJ_DEVICE_CONTROL requests
//
//Arguments:
//Pointer to our FDO
//Pointer to the IRP
//Buffered:AssociatedIrp.SystemBuffer (and IrpStack-Parameters.DeviceIoControl.Type3InputBuffer)
//Direct:MdlAddress
//
//IrpStack->Parameters.DeviceIoControl.InputBufferLength
//IrpStack->Parameters.DeviceIoControl.OutputBufferLength
//
//Return Value:
//This function returns STATUS_XXX
NTSTATUS Wdm1DeviceControl(IN PDEVICE_OBJECT fdo, IN PIRP Irp) {
 PIO_STACK_LOCATION IrpStack = IoGetCurrentIrpStackLocation(Irp);
 NTSTATUS status – STATUS_SUCCESS;
 ULONG BytesTxd = 0;
 ULONG ControlCode = IrpStack->Parameters.DeviceIoControl.IoControlCode;
 ULONG InputLength = IrpStack->Parameters.DeviceIoControl.InputBufferLength;
 ULONG OutputLength = IrpStack->Parameters.DeviceIoControl.OutputBufferLength;
 DebugPrint('DeviceIoControl: Control code %x InputLength %d OutputLength %d', ControlCode, InputLength, OutputLength);
 // Get access to the shared buffer KIRQL irql ;
 KeAcquireSpinLock(&BufferLock,&irql);
 switch (ControlCode) {
 ///////Zero Buffer
 case IOCTL_WDM1_ZERO_BUFFER:
  // Zero the buffer
  if (Buffer!=NULL && BufferSize>0) RtlZeroMemory(Buffer,BufferSize);
  break;
 ///////Remove Buffer
 case IOCTL_WDM1_REMOVE_BUFFER:
  if (Buffer!=NULL) {
   ExFreePool(Buffer);
   Buffer = NULL;
   BufferSize = 0;
  }
  break;
 ///////Get Buffer Size as ULONG
 case IOCTL_WDM1_GET_BUFFER_SIZE:
  if (OutputLength<sizeof(ULONG)) status = STATUS_INVALID_PARAMETER;
  else {
   BytesTxd = sizeof(ULONG);
   RtlCopyMemory(Irp->AssociatedIrp.SystemBuffer,&BufferSize,sizeof(ULONG));
  }
  break;
 ///////Get Buffer
 case IOCTL_WDM1_GET_BUFFER:
  if (OutputLength>BufferSize) status = STATUS_INVALID_PARAMETER;
  else {
   BytesTxd = OutputLength;
   RtlCopyMemory(Irp->AssociatedIrp.SystemBuffer,Buffer,BytesTxd);
  }
  break;
 ///////Invalid request
 default:
  status = STATUS_INVALID_DEVICE_REQUEST;
 }