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WDFREQUESTs are for sharing in KMDF v1.9

In my last post I described why a WDFREQUEST is unique to a particular WDFDEVICE.  There is one particular programming pattern where this is not the behavior you want.  This pattern is when you have each PDO accepting IO requests which it then Read More...
Posted Thursday, March 05, 2009 1:48 PM by doronh | 2 Comments
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WDFREQUESTs are not for sharing

FYI: this is a bit of a long post, but I wanted to be thorough and illustrative and give some insight into how the framework works and potential design that could have been made, but were not for the sake of simplicity and performance A common misconception Read More...
Posted Wednesday, March 04, 2009 4:58 PM by doronh | 1 Comments
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Great WinHEC presentation on device interfaces compared to device clases

[This is a repeat of a post I made to NTDEV, but I wanted to make sure I reached as many people as possible.] I just read this deck, http://download.microsoft.com/download/5/E/6/5E66B27B-988B-4F50-AF3A-C2FF1E62180F/CON-T615_WH08.pptx , which was presented Read More...
Posted Tuesday, February 03, 2009 5:03 PM by doronh | 1 Comments
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MSDN link on how to set up a user or kernel debugger

This has got to be one of the top FAQs out there: how do I set up a kernel debugger? I just stumbled across a link on MSDN which gives instructions not only on how to set up a kernel debugger on all transports (serial, 1394, usb2), but also how to set Read More...
Posted Thursday, January 29, 2009 11:15 AM by doronh | 0 Comments
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Dude, what happened to Doron?

So, I have not written anything in over 6 months and yet I have posted on NTDEV and public newsgroups. What gives? Well, the short answer is that I have been short on time these past few months. I have had only enough extra curricular time to read NTDEV Read More...
Posted Tuesday, January 27, 2009 2:09 PM by doronh | 2 Comments

How do I cancel an IRP that another thread may be completing at the same time?

Let's say that you allocated a PIRP and sent it down your device stack. You free the PIRP in the completion routine and then return STATUS_MORE_PROCESSING_REQUIRED. To make life more fun, you decide that you want to be able to cancel the sent IRP after Read More...
Posted Sunday, June 29, 2008 11:16 PM by doronh | 1 Comments
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What should you change in a sample before you ship it?

I was going to write about how to do this, but the awesome folks at WHDC got to it before I did.  I did get to review it before it was published, so I did have some influence in what is in the tip ;). So on this one my job is easy, just go read the Read More...
Posted Wednesday, April 23, 2008 11:41 AM by doronh | 0 Comments
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The WDF 1.7 cointstallers are now available

After a long wait (thank you for your patience!), the WDF 1.7 coinstallers are now up on the connect site. To get the bits go to http://connect.microsoft.com Log in using your passport account Navigate to the WDF page (I don't know where it lives in the Read More...
Posted Thursday, April 17, 2008 4:20 PM by doronh | 0 Comments
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Debugger commands (.step_filter) that make my life easier

This is a pretty cool and somewhat obscure debugger command.  It allows you to tell the debugger what functions to skip if you are using the trace command ('t').  I think of the trace command as the 'step into' command though, but that is just Read More...
Posted Wednesday, April 16, 2008 4:02 PM by doronh | 0 Comments
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EvtDevicePreprocessWdmIrp is not entirely free

One of the WDM escapes in KMDF is EvtDeviceWdmIrpPreprocess (or EvtDevicePreprocessWdmIrp in the API in which you register it) which you can register for by calling WdfDeviceInitAssignWdmIrpPreprocessCallback .  This function allows you to process Read More...
Posted Wednesday, April 02, 2008 2:14 PM by doronh | 0 Comments
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Using KeAcquireSpinLockAtDpcLevel is only a perf gain if you know you are DISPATCH_LEVEL

Well, that is certainly a long title ;). First, let us look at an approximate implementation of KeAcquireSpinLock and KeRaiseIrql (and yes I know that KeRaiseIrql is really a #define to KfRaiseIrql, but it is the same thing that happens in the end…) KIRQL Read More...
Posted Friday, March 28, 2008 3:42 PM by doronh | 1 Comments
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Inconceivableable

I have no idea who created the name for PNP_DEVICE_NOT_DISABLEABLE, but I probably have the same reaction as you ... "seriously? that is what they named?" I mean come on, I think it could have at least been named PNP_DEVICE_CANNOT_BE_DISABLED. I am sure Read More...
Posted Tuesday, March 18, 2008 4:55 PM by doronh | 1 Comments
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Once not disableable, forever not disableable

One interesting quirk about the PNP_DEVICE_NOT_DISABLEABLE state is that once it has been set and the PnP manager has processed it, the state is sticky.  By sticky I mean that even if you attempt to clear this bit on a subsequent IRP_MN_QUERY_PNP_DEVICE_STATE Read More...
Posted Tuesday, March 18, 2008 8:21 AM by doronh | 1 Comments
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Returning failure from DriverEntry

One thing that is easily overlooked about implementing DriverEntry is that upon return !NT_SUCCESS, DriverUnload is not called. I mentioned this anecdotally in a previous post , but it is worth expanding on. I was bit by this oversight when I was working Read More...
Posted Monday, March 17, 2008 4:56 PM by doronh | 0 Comments
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one of the books that started it all...

During my sophomore year at Cal Poly , I decided that I wanted to learn about threads, synchronization techniques and other topics associated modern operating systems. Windows 95 had made its debut (yes, it is not a modern OS, but I didn't know that at Read More...
Posted Wednesday, March 12, 2008 8:38 AM by doronh | 1 Comments
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