Help on IoGetDeviceObjectPointer and ObDeferenceObject

Hi,

I am using IoGetDeviceObjectPointer() API to get handle to a named device
object. In that call I am passing device object and file object as local
variables (stack variables). Once IoGetDeviceObjectPointer() returns
success, I am acquiring spin lock and copying those device object and file
object to a permanent storage. My question is do I need to call
ObDereferenceObject() for a stack variable which I passed in
IoGetDeviceObjectPointer() API? I am calling ObDereferenceObject(FileObject)
later on when I the close device stack.

The code is something like this.

Status = IoGetDeviceObject(xxx, xxx, &TempFO, &TempDO).

if (NT_SUCCESS(Status) {

Acquire spin lock;

PermFO = TempFO;
PermDO = TempDO;

Release spin lock;
}

CloseStack() {
ObDereferenceObject(PermFO);
}

My question is do I need to ObDereferenceObject(TempFO) somewhere in the
code?????

Thanks.

No, making a copy of a pointer is not going to increment the objects
reference count. So only when you do an explict call that changes the
reference count do you need to worry.

--
Don Burn (MVP, Windows DDK)
Windows 2k/XP/2k3 Filesystem and Driver Consulting
Remove StopSpam from the email to reply




"Nikhil" <> wrote in message
news:AE9D47D4-62E9-4902-B3E1-...
> Hi,
>
> I am using IoGetDeviceObjectPointer() API to get handle to a named device
> object. In that call I am passing device object and file object as local
> variables (stack variables). Once IoGetDeviceObjectPointer() returns
> success, I am acquiring spin lock and copying those device object and file
> object to a permanent storage. My question is do I need to call
> ObDereferenceObject() for a stack variable which I passed in
> IoGetDeviceObjectPointer() API? I am calling
> ObDereferenceObject(FileObject)
> later on when I the close device stack.
>
> The code is something like this.
>
> Status = IoGetDeviceObject(xxx, xxx, &TempFO, &TempDO).
>
> if (NT_SUCCESS(Status) {
>
> Acquire spin lock;
>
> PermFO = TempFO;
> PermDO = TempDO;
>
> Release spin lock;
> }
>
> CloseStack() {
> ObDereferenceObject(PermFO);
> }
>
> My question is do I need to ObDereferenceObject(TempFO) somewhere in the
> code?????
>
> Thanks.
>

Thank you for a quick response.

"Don Burn" wrote:

> No, making a copy of a pointer is not going to increment the objects
> reference count. So only when you do an explict call that changes the
> reference count do you need to worry.
>
> --
> Don Burn (MVP, Windows DDK)
> Windows 2k/XP/2k3 Filesystem and Driver Consulting
> Remove StopSpam from the email to reply
>
>
>
>
> "Nikhil" <> wrote in message
> news:AE9D47D4-62E9-4902-B3E1-...
> > Hi,
> >
> > I am using IoGetDeviceObjectPointer() API to get handle to a named device
> > object. In that call I am passing device object and file object as local
> > variables (stack variables). Once IoGetDeviceObjectPointer() returns
> > success, I am acquiring spin lock and copying those device object and file
> > object to a permanent storage. My question is do I need to call
> > ObDereferenceObject() for a stack variable which I passed in
> > IoGetDeviceObjectPointer() API? I am calling
> > ObDereferenceObject(FileObject)
> > later on when I the close device stack.
> >
> > The code is something like this.
> >
> > Status = IoGetDeviceObject(xxx, xxx, &TempFO, &TempDO).
> >
> > if (NT_SUCCESS(Status) {
> >
> > Acquire spin lock;
> >
> > PermFO = TempFO;
> > PermDO = TempDO;
> >
> > Release spin lock;
> > }
> >
> > CloseStack() {
> > ObDereferenceObject(PermFO);
> > }
> >
> > My question is do I need to ObDereferenceObject(TempFO) somewhere in the
> > code?????
> >
> > Thanks.
> >
>
>
>