In an earlier post, I described a subtle race condition resulting from the differing lifetimes of miniport adapters and control device objects. Last week, Gianluca Varenni, the maintainer of WinPcap and one of the brains at CACE technology, pointed out that Microsoft had recently changed the Passthru sample to add reference counting in some instances to adapter objects. I went back and looked, and sure enough, the current DDK WDK sample has additional reference counting built into the driver.
Microsoft didn’t add any comments to the sample describing the reference counting addition, but I found this bug myself a while ago and implemented essentially the same solution. The basic problem is that there is a race between the two different adapter tear-down paths – the one that is initiated from halting the virtual miniport itself and the other that is triggered by the halting of the underlying miniport.
Gianluca also pointed out that nobody in their right mind would write an IM driver from scratch, other than as an educational experience, because it’s entirely too difficult to get the various NDIS synchronization issues right unless you’re an absolute expert at it. Obviously, even Microsoft is still finding bugs.
The good news is that IM’s are dead. Vista has a much-improved lightweight filtering architecture, so the writing is no the wall.
What’s it going to be like getting to ship actual production code with the WDK? I can’t wait to strip out all of the #ifdefs for the old kits…