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August 2006 - Posts

How do I debug a failed device install or disable?

Debugging a failed device install or disable can be tough. The error could be hidden in the depths of the system and it might take awhile to figure it out. The error code on the device might be of some help, but it is not always clear. For instance, you Read More...
Posted Thursday, August 31, 2006 4:49 PM by doronh | 5 Comments
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Symbolic links need protection?

It is not like I go read the WDK docs in my spare time, but one day I did and I came across IoCreateUnprotectedSymbolicLink . Huh? An unprotected symbolic link? I knew about IoCreateSymbolicLink (which by induction would be a protected symlink), but I Read More...
Posted Tuesday, August 29, 2006 5:24 PM by doronh | 0 Comments
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I want my sleep key back! (or how to hibernate a machine from your app)

One of the first things I do when I get a new desktop machine or install a new build of Windows is to map the Sleep button on my keyboard to hibernate instead of suspend. Hibernate makes more sense for these machines because they will never run on batteries Read More...
Posted Monday, August 28, 2006 2:41 PM by doronh | 11 Comments

A NULL and zero wait timeout are not the same

When you call KeWaitForSingleObject or KeWaitForMultipleObjects you can provide a pointer to a timeout value. What value you pass for the pointer value makes a huge difference. This subtle distinction is something that first time driver writers do not Read More...
Posted Friday, August 25, 2006 5:22 PM by doronh | 5 Comments
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How do I know which symbolic link is being opened?

In my last post I showed how you can distinguish between to different device interfaces being opened on the same device object. While device interfaces are the Microsoft party line for how to expose a PnP device object which can be opened, I realize that Read More...
Posted Wednesday, August 23, 2006 4:46 PM by doronh | 0 Comments
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How do I know which device interface is being opened?

Let's say your device supports two interfaces and you want to expose both of them on the same device object. Furthermore, let's say that the I/O interface to each device interface is different. For instance, let's say that one interface allows only one Read More...
Posted Friday, August 18, 2006 4:08 PM by doronh | 2 Comments
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New for Windows Vista: thread agnostic I/O

When an I/O is issued on behalf of a system service call (for example NtReadFile, NtWriteFile, etc), the I/O manager creates a threaded IRP and then issues the I/O. I previously wrote about this. Today, Paul has returned as a guest writer and will talk Read More...
Posted Thursday, August 17, 2006 9:14 AM by doronh | 3 Comments
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Formatting a WDFREQUEST for any IRP_MJ code

In KMDF, the WDFIOTARGET object provides an abstraction for sending I/O to another PDEVICE_OBJECT and tracking all pending I/O. The WDFIOTARGET also provides formatting for specific types of I/O: read, write, IOCTL, and internal IOCTL. The WDFUSBDEVICE Read More...
Posted Wednesday, August 16, 2006 4:26 PM by doronh | 1 Comments
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Look Ma, I'm on Channel 9!

I was interviewed for channel 9 a couple of weeks ago, you see the interview here . We talked about KMDF, the state machines and the future of driver development. I had a great time doing the interview, hopefully you like it as well. Please let me know Read More...
Posted Tuesday, August 15, 2006 1:02 PM by doronh | 5 Comments

Debugger command (!list) that makes my life easier

Yesterday I introduced the dl command and demonstrated some of its limitations. Today I will talk about !list . Let's take yesterday's data structure, MY_DATA. What if the LIST_ENTRY is at the end of the structure or there is more data in your structure Read More...
Posted Thursday, August 10, 2006 8:06 AM by doronh | 7 Comments
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Debugger command (dl) that makes my life easier

The use of the LIST_ENTRY structure in WDM is quite pervasive. It is used for nearly all list keeping tasks. I have used it extensively in the past and KMDF uses it quite a bit as well. There are two debugger commands that help in viewing the contents Read More...
Posted Wednesday, August 09, 2006 3:34 PM by doronh | 2 Comments
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IoSetCompletionRoutineEx is not a drop in replacement for IoSetCompletionRoutine

Yesterday I wrote about the evolution of work items. Work items evolved because there was a need to have a reference on the device object until the work item's callback routine returned. As I illustrated yesterday, there is a small piece of assembly in Read More...
Posted Tuesday, August 08, 2006 12:49 PM by doronh | 3 Comments
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Why is there an Ex and Io work item in WDM?

Have you ever looked at the work item APIs and wondered why there are two different types of work items? Or for that matter, why are there so many work item APIs? As Paul wrote last week, the work item API set has grown for Vista. Today I will try to Read More...
Posted Monday, August 07, 2006 4:49 PM by doronh | 8 Comments
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Turning setupapi logging up to 11

When debugging a failed device install, one of the first things you should do is look at the %windir%\setup*.log files (yes files, there are a few of them and the names changed in Vista). But what if the logs do not have enough information for you to Read More...
Posted Friday, August 04, 2006 8:09 AM by doronh | 1 Comments

Enhanced Work Item Support in Vista

While writing the threaded and non-threaded PIRP entry, I had the I/O manager developers review what I wrote to make sure I was giving out correct information. After the review, the I/O manager folks wanted to know if they could write some guest entries Read More...
Posted Thursday, August 03, 2006 8:05 AM by doronh | 2 Comments
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Viewing your KMDF log in a mini-dump (and other post mortem features)

Your KMDF driver log can also be available in a mini-dump under certain circumstances. If you have a full kernel dump or a full memory dump, the log will be always present (barring any memory corruption or problems writing out the dump file). KMDF will Read More...
Posted Wednesday, August 02, 2006 4:03 PM by doronh | 0 Comments
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Customizing the KMDF log for your driver

Yesterday I talked about the KMDF log. The KMDF log is a great tool to debug why a DDI call has failed or diagnose the cause of a bugcheck in your driver. You can customize different attributes of the log so that you can better debug your driver. The Read More...
Posted Tuesday, August 01, 2006 3:55 PM by doronh | 0 Comments
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