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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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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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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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How to share HW resources with another driver not in the same PnP hierarchy

First, I have to say that I don't agree with this design pattern at all . I think it leads to too many problems and complications that are not worth the pain. The only reason I am writing this entry is that I have seen so many people get this wrong or Read More...
Posted Wednesday, October 24, 2007 3:56 PM by doronh | 1 Comments
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WdfDeviceRetrieveDeviceInterfaceString and PDOs

When you initially create a PDO, it takes a few steps for PnP to recognize it. I wrote this problem of determining when a PDO becomes a PDO last year . At the end of the post I mentioned that KMDF handles all of this state management for you underneath Read More...
Posted Monday, October 22, 2007 4:56 PM by doronh | 1 Comments
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Setting a security descriptor on a legacy device object

Setting the security descriptor allows you to control who can open a handle to the device object. Typically you can call IoCreateDeviceSecure to create the device object and have the correct DACL from the start. One issue with IoCreateDeviceSecure is Read More...
Posted Tuesday, October 16, 2007 4:45 PM by doronh | 1 Comments
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Having two names is not necessarily better than one, part 2

Previously I wrote about what happens when there are 2 devices in a stack with a name and all of the associated issues that arise from it. In that vein I want to write about what happens when you give your device object a name in KMDF and compare it to Read More...
Posted Thursday, July 12, 2007 11:10 AM by doronh | 0 Comments
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Problems with not having a current IRP stack location, part 2

This problem falls into the category being hidden by a macro that does not indicate in its name what it touches. If you call IoMarkIrpPending on an IRP that you allocated in your driver, chances are that you are corrupting memory. First, let's look at Read More...
Posted Monday, April 09, 2007 9:04 AM by doronh | 2 Comments
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Filtering HID collections and setting I/O flags

Over the past 3 years or so, I have been casually referring to KMDF as the ultimate driver compat layer. Just like Windows has an application compatibility layer which shields applications from OS changes, KMDF provides the same type of compatibility Read More...
Posted Monday, March 26, 2007 5:19 PM by doronh | 4 Comments
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Supporting query interface in KMDF

In my last post I talked about bidirectional interfaces which can have both input and output parameters. KMDF supports both unidirectional and bidirectional interfaces. As is the case with many KMDF APIs and behaviors, we allow you to implement the easy Read More...
Posted Monday, March 12, 2007 11:25 AM by doronh | 0 Comments
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Power relationships in a bus driver

A small but important rule in WDM is that while a PDO is in D0, the parent must be in D0 as well. A very simple statement that can cause a lot of trouble ;). What I have seen is that very few WDM drivers enforce this rule (while KMDF does implement this Read More...
Posted Friday, March 02, 2007 5:28 PM by doronh | 1 Comments
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Problems associated with arming yourself for wake

Hindsite in this case is 20/20, but arming your device for wake can open yourself up to multitude of race conditions and hard problems. Some of them you can solve in your driver, some of them you must accept that they are there and leave them be. Arming Read More...
Posted Tuesday, February 27, 2007 2:59 PM by doronh | 0 Comments
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I can't imagine how much work it would be to actually /write/ a book

All I can say is that it is a ton of work to review one. We just finished all of the reviews for the WDF book and man was it alot of work! We have an awesome set of writers, I really don't know how they managed it all. From creating the content, taking Read More...
Posted Tuesday, February 20, 2007 5:27 PM by doronh | 0 Comments
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Which PnP and power IRPs are synchronized against each other?

In my previous post , I talked about how state changing PnP IRPs (refered to from now own as just PnP IRPs) are serialized against each other and briefly mentioned which power IRPs they were synchronized against. This merits its own entry. In short, PnP Read More...
Posted Tuesday, February 06, 2007 10:26 PM by doronh | 1 Comments
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