96 lines
3.4 KiB
Plaintext
96 lines
3.4 KiB
Plaintext
IRP Cancellation
|
|
|
|
1. An internal spinlock (ntoskrnl!IopCancelSpinLock) is always
|
|
acquired before invoking a cancel routine. The previous IRQL
|
|
can be found at pIrp->CancelIrql. The cancel routine MUST release
|
|
the spinlock by calling IoReleaseCancelSpinLock() before returning.
|
|
Code may call IoAcquireCancelSpinLock() as necessary, but don't
|
|
party on it too much. It's a huge source of contention within the
|
|
kernel.
|
|
|
|
2. You can never complete an IRP that still has a non-NULL cancel
|
|
routine pointer. You MUST set the cancel routine pointer to NULL
|
|
before calling IoCompleteRequest().
|
|
|
|
3. You cannot set a cancel routine and then pass the IRP to another
|
|
driver. If you're going to pass the IRP to another driver (say, a
|
|
lower-level driver) you MUST set the cancel routine to NULL before
|
|
calling IoCallDriver().
|
|
|
|
4. IoSetCancelRoutine() returns the previous cancel routine pointer.
|
|
It's possible that you are in the midst of completing an IRP and
|
|
call IoSetCancelRoutine() to set the cancel routine pointer to
|
|
NULL, and IoSetCancelRoutine() returns NULL. This typically means
|
|
that the cancel routine is running or about to run Real Soon Now.
|
|
|
|
5. The pIrp->Cancel flag is set in IoCancelIrp() BEFORE the cancel
|
|
routine pointer is extracted from the IRP and invoked.
|
|
|
|
6. IoCancelIrp extracts the Irp using IoSetCancelRoutine(NULL) . So
|
|
you can detect if it has extracted your cancel routine by later
|
|
calling IoSetCancelRoutine (which returns the previous value) .
|
|
|
|
7. Drivers check pIrp->Cancel AFTER setting a CancelRoutine in order
|
|
to detect the case of the Irp being cancelled while your setting
|
|
the CancelRoutine. If it is TRUE, using #4 above to detect if
|
|
IoCancelIrp knows about your CancelRoutine. If it does not,
|
|
you must complete the irp yourself. An easy way to do this is
|
|
to manually call your CancelRoutine.
|
|
|
|
IoSetCancelRoutine(pIrp, &CancelRoutine);
|
|
|
|
if (pIrp->Cancel)
|
|
{
|
|
//
|
|
// Irp was canceled.
|
|
//
|
|
|
|
//
|
|
// Did IoCancelIrp consume our CancelRoutine?
|
|
//
|
|
|
|
if (IoSetCancelRoutine( pIrp, NULL ) != NULL)
|
|
{
|
|
//
|
|
// Nope. This means our cancle routing will
|
|
// NOT be called by IoCancelIrp. We better call it
|
|
//
|
|
|
|
IoAcquireCancelSpinLock(&pIrp->CancelIrql);
|
|
CancelRoutine(g_pDeviceObject, pIrp);
|
|
}
|
|
|
|
//
|
|
// do not use pIrp anymore
|
|
//
|
|
}
|
|
else
|
|
{
|
|
//
|
|
// safe to queue pIrp. If it is cancelled the CancelRoutine
|
|
// will be called.
|
|
//
|
|
}
|
|
|
|
|
|
7. x
|
|
|
|
|
|
|
|
Pending
|
|
|
|
1. If you return STATUS_PENDING from an IOCTL handler, then you
|
|
must first call IoMarkIrpPending().
|
|
|
|
2. If you take an incoming IRP, build another stack location,
|
|
and call IoCallDriver(), you must set a completion routine and
|
|
the completion routine must propagate the pending flag:
|
|
|
|
if( pIrp->PendingReturned )
|
|
{
|
|
IoMarkIrpPending( pIrp );
|
|
}
|
|
|
|
3. x
|
|
|