Writing Windows Port Monitor Basics

Question

I'm trying to find a basic example, tutorial, or blog post on how to write a printer port monitor. I downloaded the Windows DDK and dug through localmon, but it appears that this sample is much more complex than just the nuts and bolts basics and from my understanding it is a bit different than an OEM port monitor because of how it handles the registry key and port enumeration. Does anyone know of a blog post, tutorial, or even book that walks the reader through the basic code to get one up and going? I've found a few links talking about the conceptual stuff, but nothing that is hands on code.

Answer 1

I have been over that exact same territory for a serial printer. About the best example I found was this article in Dr Dobbs Journal. The good part is that both a serial port driver and the user-space control program are covered and the project can also be used as an example of how to set up Visual Studio to compile a driver. This is also something a little difficult to find information about. The article discusses an old NT style driver, which worked well for me on XP.

There are quite a few good articles on CodeProject about writing drivers and programs to interact with them. They include source code and most deal with the newer WDM and WDF style drivers.

OSROnline is another good source, especially for discussion of specific issues and common mistakes. They also have some great utilities you will need.

Some of the most clearly written and understandable driver code I came across was Mark Russinovich's sample code. Although Microsoft withdrew all of the source when they purchased Sysinternals, some of the best examples can still be found cached here and there.

Drivers are pretty interesting. Whatever else you do though, do it in a virtual machine. Really.

Answer 2

I wrote mine from the specs, there aren't really that many API's to implement.

The one thing that regularaly trips people up is EnumPorts, the spooler allocates enough memory for ALL the ports, not just yours. So you need to make sure you fill any strings from the end of the spoolers buffer, don't put them straight after your structures.

It doesn't say so in the specs but you can safely put the UI and Server functions in the same DLL.

It's also possible to create a single port monitor that supports NT and the later Windows 2000 type port monitors.

The code in RedMon is much easier to read than the localmon example, it's worth looking at before you start. It's quite nice because you can compile it in VS, you don't need to use the DDK to build it.

Answer 3

I can recomend http://www.codeproject.com/KB/printing/wpa.aspx, which describes how to write a printer driver and also has good hints about what's necessary to build a port monitor.

But my opinion is that a good tutorial in this area is not available on the Internet (I would be glad to find somebody who can show me that I'm wrong). So, when I had to deal with this task I was forced to do it the hard way: I've read carefully the MSDN explanations starting from this point: http://msdn.microsoft.com/en-us/library/ms802196.aspx. In parallel with reading MSDN I also checked the code in DDK you mentioned and try to understand it. I'm sure this solution could also work for you.