typedef struct _DEVOBJ_EXTENSION
{
     SHORT Type;
     WORD Size;
     PDEVICE_OBJECT DeviceObject;
     ULONG PowerFlags;
     PDEVICE_OBJECT_POWER_EXTENSION Dope;
     ULONG ExtensionFlags;
     PVOID DeviceNode;
     PDEVICE_OBJECT AttachedTo;
     LONG StartIoCount;
     LONG StartIoKey;
     ULONG StartIoFlags;
     PVPB Vpb;
} DEVOBJ_EXTENSION, *PDEVOBJ_EXTENSION;

Windows Vista Kernel Structures