IoGetDeviceObjectPointer on serial driver !!

[Thomas Johansen]

Hi

The first time I call IoGetDeviceObjectPointer on \Device\Serial0 the
function call do not fail.
Any attempts to open the COM port from user mode app. fails, which is fine.

But when I stop the driver i stil can't open the COM port from a user mode
app. ??
In my DriverUnload function I do call ObDereferenceObject() on the
fileobject returned by IoGetDeviceObjectPointer.

Any further attempts to call IoGetDeviceObjectPointer on \Device\Serial0
fails, (with error code 3221225506) which according to the DDK help files,
can't be returned ?

Isn't IoGetDeviceObjectPointer a combination of ZwCreateFile,
ObReferenceObjectByHandle, IoGetRelatedDeviceObject, ZwClose ??
So why can't I reopen the COM port ??

Thomas

 

[Gary G. Little]

Deref the device object that you get back as well.

 

[Walter Oney]

But when I stop the driver i stil can't open the COM port from a user mode
app. ??
In my DriverUnload function I do call ObDereferenceObject() on the
fileobject returned by IoGetDeviceObjectPointer.

Are you sure DriverUnload is being called? Are you sure you've got the
right FileObject pointer? Given that you're handling this operation in
DriverUnload, you must be using a static variable to hold the pointer.
That's not a very good idea, since each instance of your device should
have its own unique value.

Any further attempts to call IoGetDeviceObjectPointer on \Device\Serial0
fails, (with error code 3221225506) which according to the DDK help files,
can't be returned ?

Shame on you for not translating this to hex -- C0000022 --
STATUS_ACCESS_DENIED, which is exactly what you'd expect if SERIAL
thought a handle was still open.

 

[Alexander Grigoriev]

No, you should NOT dereference the devobj. You only need to dereference the
file object. The file object itself keeps a reference to the devobj.

 

[Gary G. Little]

Really? Then why is it that I have to use ObDereferenceObject on the
DeviceObject passed back to me from IoGetDeviceObjectPointer, to get that
device to close? Decrementing the reference count on the file object alone
does not do it.

 

[Spiro Trikaliotis]

Hello,

Really? Then why is it that I have to use ObDereferenceObject on the
DeviceObject passed back to me from IoGetDeviceObjectPointer, to get that
device to close? Decrementing the reference count on the file object alone
does not do it.

According to Walter Oney's book and the DDK documentation, you have to
dereference the file object only. Are you sure you do not call
ObReferenceObject() on the device object yourself?

Kind regards,
Spiro.

 

[Gary G. Little]

I was incorrect. I've been testing this for a problem for the past few days
and did not have things set up the way I "thought" I had them when I made
the post. I have indeed been passing the FileObject to ObReferenceObject and
not the DriverObject.

 

[Thomas Johansen]

No, you should NOT dereference the devobj. You only need to dereference
the

file object. The file object itself keeps a reference to the devobj.

Yes. I do that, but still my COM port isn't released and I have to reboot
!!!

This is what I do in my opne COM function:

status = IoGetDeviceObjectPointer(&wstrComPort, FILE_ALL_ACCESS,
&FileObject, &DeviceObject);

KeInitializeEvent(&evt, NotificationEvent, FALSE);
pIrp = IoBuildDeviceIoControlRequest(IOCTL_SERIAL_SET_BAUD_RATE,
AttachedDeviceObject, (PUCHAR)&br, sizeof(br), NULL, 0, FALSE, &evt, &ios);

if (pIrp != NULL)
{
status = IoCallDriver(AttachedDeviceObject, pIrp);
if (status == STATUS_PENDING)
{
KeWaitForSingleObject(&evt, Executive, KernelMode, FALSE, NULL);
status = ios.Status;
}
}

This code seems to work.
In my XXXUnload function i do this:

if(FileObject != NULL)
{
KdPrint(("Closing the COM port.\r\n"));
ObDereferenceObject(FileObject);
}

But after this the COM port isn't released ?

Am I doing something wrong here ?

Thomas

 

[Thomas Johansen]

And in my system log I get the following error message:

"The system cannot find the file specified" Error 7000

 

[Thomas Johansen]

And in my system log I get the following error message:

"The system cannot find the file specified" Error 7000

 

[Alexander Grigoriev]

What is AttachedDeviceObject and how it corresponds to DeviceObject?

 

[Thomas Johansen]

Hey again.

From my COM open function:

PFILE_OBJECT FileObject = NULL;
PDEVICE_OBJECT DeviceObject = NULL;
PDEVICE_OBJECT AttachedDeviceObject = NULL;


// Get device object pointer
status = IoGetDeviceObjectPointer(&wstrComPort, FILE_ALL_ACCESS,
&FileObject, &DeviceObject);

// Check status
if (NT_SUCCESS (status))
{
// Create unknown device
status = IoCreateDevice(DriverObject,
0,
NULL,
FILE_DEVICE_UNKNOWN ,
0,
FALSE,
&pDeviceObject );

if(NT_SUCCESS (status))
{
// Attach the next lower to this stack
AttachedDeviceObject = IoAttachDeviceToDeviceStack(pDeviceObject,
DeviceObject);

if(NULL != AttachedDeviceObject)
{
// initialize the baudrtate structure baudrate
RtlZeroMemory(&baudRate, sizeof(baudRate));
baudRate.BaudRate = nBaudRate;

// Initialize the event
KeInitializeEvent(&evt, NotificationEvent, FALSE);

// Build the IRP
pIrp = IoBuildDeviceIoControlRequest(IOCTL_SERIAL_SET_BAUD_RATE,

AttachedDeviceObject,

(PUCHAR)&baudRate,

sizeof(baudRate),

NULL,
0,

FALSE,

&evt,

&IoStatusBlock);

if (pIrp != NULL)
{
// Set the baud rate
status = IoCallDriver(AttachedDeviceObject, pIrp);

// If pending wait for completion
if (status == STATUS_PENDING)
{
KeWaitForSingleObject(&evt, Executive, KernelMode, FALSE,
NULL);
status = IoStatusBlock.Status;
}
}
else
{
KdPrint(("IoBuildDeviceIoControlRequest failed.
STATUS_INSUFFICIENT_RESOURCES\n"));
status = STATUS_INSUFFICIENT_RESOURCES;
}
}
}

I do this in my Unload function:

//Close the COM port.
IoDetachDevice(DeviceObject);
ObDereferenceObject(FileObject);

Hope this helps... By the way. All serial port operation works fine. Exept
that the port is released for the system again..

Thomas

 

[Alexander Grigoriev]

1. You don't need to attach your device object.
2. You're detaching wrong device object.

 

[Thomas Johansen]

Hi Alexander

1. You don't need to attach your device object.

You where completly right !!! Thanks

2. You're detaching wrong device object.

Schould I use IoDetachDevice(..) on the Device object from
IoGetDeviceObjectPointer call ?
I have tried. Doesn't work

In the DDK help the IoDetachDevice schould be used on devices returned from
IoAttachDevice or IoAttachDeviceToDeviceStack ?
As in number 1, I don't need to attach the device ??

So I still can't find out, how to close the COM port !!!!


Thomas

 

[Thomas Johansen]

Hi again

I got my self a big cup of coffee and firgured it out myself..

Thanks for the time and help

Thomas

 

[Gary G. Little]

Long time ago this came up and I boloxed up the answer. Are you doing an
ObDereferenceObject on the file object pointer you get back from the call to
IoGetDeviceObjectPointer?