From: bmckenzie@bsquare.com
Sent: Tuesday, March 05, 2002 1:16 AM
To: NT Developers Interest List
Subject: [ntdev] Re: Problem delaying the completion of an Irp

Carlo,

If there is even a remote chance you might delay the completion of the
create IRP to some time after your completion routine returns, then you
must, from your dispatch routine, call IoMarkIrpPending and return
STATUS_PENDING explicitly.  This is not documented very well, and I
believe I entered a bug on this in the bug bash.

Normally, your completion routine will complete the IRP, so you can just
return what is returned to you from your IoCallDriver call in your
dispatch routine.  If the IRP is not completed in the completion routine,
then your return from IoCallDriver may not reflect the true status of the
IRP, in that you may get a STATUS_SUCCESS return from IoCallDriver, even
though your driver has yet to complete the IRP.  Then, if you return this
STATUS_SUCCESS from your dispatch routine in this case the driver layered
over yours will not know the IRP is still pending in your driver.

To understand why this is so, I highly recommend you read this:

http://www.osr.com/ntinsider/1997/iocomp/iocomp.htm

Its complicated stuff, you definitely aren't the first to get your head
wrapped around the axle on this one.

Interestingly enough, everyone working on WDM drivers that are power
policy owners, (that is most device drivers), should have run into this by
now.  You cannot properly handle system power IRPs without hitting this
situation.  According to the DDK docs system power IRPs should be
completed by power policy owners in the associated device power IRP's
power completion routine.  But alas, most drivers aren't doing this,
including most DDK samples.

Bill M.



In fact, reading the docs didn't solve my doubts. In all other Irps
I set a completion routine for, I simply ended the dispatch routine
with a "return IoCallDriver(...)"; this should work since I never had
to further delay the Irp completion in my completion routine.
In the case of the Create Irp, instead, IoCallDriver() surely doesn't
return STATUS_PENDING, so mending the dispatch routine as you suggested
solved the problem. My doubt is now the following: suppose I can't tell
until my completion routine is called if the Irp completion has to be
delayed; in this case I have to pend the Irp anyway in the dispatch
routine and return from the completion routine STATUS_SUCCESS (or error)
if the Irp has to be completed immediately and STATUS_MORE_PROCESSING_
REQUIRED if I need to delay the completion?

Thank you again

Carlo Andreoli

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