What is the use of IrpSp->Parameters.MountVolume.DeviceObject?

NTFSD
1

Hi, experts,

In handling IRP_MN_MOUNT_VOLUME, we have four device objects.

Say:

NTSTATUS DispatchFsControl(PDEVICE_OBJECT DeviceObject1, PIRP Irp)
{
IrpSp->Parameters.MountVolume.Vpb.RealDevice; // DeviceObject2
IrpSp->Parameters.MountVolume.Vpb.DeviceObject; // DeviceObject3

IrpSp->Parameters.MountVolume.DeviceObject; // DeviceObject4
}

To my understanding,

1, DeviceObject1 is the file system, say L"\Ntfs".

2, DeviceObject2 is the partition device, say L"\Device\HarddiskVolume1".

3, DeviceObject3 is the volume device created in this routine to respond to
IRP_MN_MOUNT_VOLUME, say L"FileSystem\Ntfs".

4, DeviceObject4 is ???

http://www.osronline.com/showThread.cfm?link=25276
and
http://www.osronline.com/showThread.cfm?link=22666

The preceding two postings discussed this question. However, I’m still
unclear.

In the latter posting, Neal from Microsoft says:

"I don’t know if you are writing a filter or file system, but in either case
you want to ignore this parameter. "

If what he says is true, then what is the intent to reserve such a field?

2

> 1, DeviceObject1 is the file system, say L"\Ntfs".

Yes.

2, DeviceObject2 is the partition device, say L"\Device\HarddiskVolume1".

Yes, bottom of partition stack.

IIRC the top of partition stack.

–
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
xxxxx@storagecraft.com
http://www.storagecraft.com

3

Thank you, Maxim.

What I want to know is: For an FSD writer, when and where to use the field
IrpSp->Parameters.MountVolume.DeviceObject?

Someone says FSD writers should ignore this field. But I can’t understand
the reason why Microsoft reserves such an device object.

I can’t understand WHY an FSD needs the top device object of the storage
stack.

“Maxim S. Shatskih” xxxxx@ntfsd…
>> 1, DeviceObject1 is the file system, say L"\Ntfs".
>
> Yes.
>
>> 2, DeviceObject2 is the partition device, say
>> L"\Device\HarddiskVolume1".
>
> Yes, bottom of partition stack.
>
> IIRC the top of partition stack.
>
> –
> Maxim Shatskih, Windows DDK MVP
> StorageCraft Corporation
> xxxxx@storagecraft.com
> http://www.storagecraft.com
>
>

4

> What I want to know is: For an FSD writer, when and where to use the field

IrpSp->Parameters.MountVolume.DeviceObject?

Someone says FSD writers should ignore this field. But I can’t understand
the reason why Microsoft reserves such an device object.

This is the current top of disk stack to send IRPs to.

–
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
xxxxx@storagecraft.com
http://www.storagecraft.com