Why can’t you un-pend an IRP?
I was playing around with SDV and the pending bit the other day, and tried setting and clearing it in back-to-back lines in a dispatch routine. Having CSQ mark the IRP pending (which is automatic, if it succeeds at queuing the IRP) caused SDV to blow up with a very confusing error.
According to a PowerPoint slide by Adrian Oney, here’s the reason:
There is no IoUnmarkIrpPending because a driver above you can legally mark your stack location pending and return STATUS_PENDING
He goes on to say that PoCallDriver does this. News to me! I had always wondered why it was illegal (as opposed to simply immoral) to mark and un-mark an IRP as pending; it’s because in so doing, you would destroy the state of the driver above you who was depending on this.
December 3rd, 2006 at 4:22 am
Of course, because the IRP structure isn’t opaque, I’m sure there’s at least one driver out there that removes the flag manually.
(And the people who ship drivers using that kind of code don’t usually use SDV).