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Overview and usageFileObjectInfo is a tool which lets you take a look at Windows NT's file objects. In contrast to NTHandleEx from www.sysinternals.com and EnTeHandle article from Fred Forester (contributed here at CodeGuru) it also shows some of the corresponding device object properties, like the actual device name.
FileObjectInfo walks the systems handle table and looks for all handles which refer to file objects. In Windows NT not only files which reside on disk are represented by a file object. File objects are also used to access communication devices, input/output devices and so on. FileObjectInfo shows information about the file objects and the device they belong to. This is especially useful, if the file object is unnamed, e.g. in case of the serial communication ports (see screenshot below).
Each file object is shown in one line, listing its owners process id
and name, the device type/name of the device which it refers to and
the actual file name (or "no name" if it is unnamed). To allow easy
viewing and browsing of all file objects, you can group and sort the
display columns. To group by a column use the main menus
view --> group by... items. This will group all file objects
with the same group name into a node of a tree view (see 
for more information on the treeview list control used). To sort just click
one of the column headings. In case you want to refresh the display, i.e.
reread the systems handle table, you can use view --> refresh.
Personally i am using FileObjectInfo to find answers to questions like: "What process has opened COM1?" (Try it yourself: group by "device type" and expand the tree node FILE_DEVICE_SERIAL_PORT!).
For some notes on installing and running FileObjectInfo, see the end of this article.
The following picture shows what happens inside the application/driver combo.
The user mode application uses a few undocumented calls into NTDLL.DLL (NtQuerySystemInformation, see ) to get information about all open handles and all running processes. Each entry (SYSTEM_HANDLE) of the handle list (shown as SystemHandleList in the picture above) contains some information about the handle. Of particular interest are:
- ProcessID: Used to display the owners process name
- ObjectType: Type of Object (e.g. OB_TYPE_FILE == File-Object)
- *pObject: Address of the kernel mode data structure for this object
In case of a file object (FILE_OBJECT, which is fortunately documented (!) in the DDK, see ) the driver uses the embedded pointer *pDeviceObject to get the refering DEVICE_OBJECT. Using this pointer it builds a structure containing the device objects name (using the officially undocumented ObQueryNameString, but see ) and the type of the device object. This structure is then returned to the user mode application and gets displayed in the GUI.
Some special stuff
Undocumented information classesI mixed the information and source codes from  and  and build some new classes to easily use the undocumented NtQuerySystemInformation function. There is a common base class NtSystemInformation from which the following two classes are derived:
- NtSystemHandleInformation: read the systems handle table
- NtSystemProcessInformation: read the systems process table
Embedded dynamic loaded driverI do not like the idea of having multiple files for a small application. However, FileObjectInfo actually consists of two components: the application executable and the kernel mode device driver. Help came from an article in the Microsoft System Journal (see ), which described a method to embed a device driver image into the resource section of an application.
On startup FileObjectInfo extracts the driver image from its ressources and writes it to a temporary file on the hard disk. It then registers and starts the driver and removes the temporary file. From now on the driver can be used normally. When FileObjectInfo is closed (an thus the driver is no longer used) it stops and unregisters the driver.
All functions for dynamically loading and unloading a driver are contained in the file "dynamic.cpp".
Addtional ideasAt the moment, FileObjectInfo (as its name implies) is restricted to show additional information for file objects only. However, the application as well as the driver can easily be expanded to support other object types. Maybe it could be expanded to show system data structures like WinDBG or SoftIce without having to actually use a debugger.
-  James Finnegan, Pop Open a Privileged Set of APIs with Windows NT Kernel Mode Drivers, Microsoft System Journal, March 1998
-  Sven B. Schreiber, Inside Windows NT System Data, Windows Developer Journal, November 1999
-  Windows NT DDK, can be freely downloaded from Microsofts web site
-  Fred Forester, EnTeHandle article on CodeGuru
-  System Internals source code, www.sysinternals.com
-  Multi column tree control by David Lantsman, published here
Compiling the sourcesIn order to make FileObjectInfo work on Windows 2000 and Windows NT, the device driver has to be built using the NT4 DDK. The supplied Visual C++ 6 workspace will work correctly, if you set the environment variable BASEDIR to the root directory of your NT4 DDK installation.
Note: As i did not get Visual C++ to recognize the dependencies between the two projects (driver and gui) right, you should build the driver first, then build the gui.
Installing and running FileObjectInfoTo install FileObjectInfo, just copy its executable "FileObjectInfo.exe" to a directory on your local hard disk. It will not run from a network locatiton nor will it run from a location where you don't have write access (it will create a temporary file in the same directory where it is installed).
As it has to register and start a kernel mode driver, you need administrative privileges to run FileObjectInfo.
WARNING: This is experimental software which uses undocumented functions, installs a kernel mode driver and peeks around in your systems internals. Although this software works very well for me, i can't guarantee it will work this way for every possible hardware/software kombination out there.
Be warned and don't blame me, if it bluescreens...
- August 7, 2000
- Initial posting
- February 9, 2001
- Enhanced GUI
- Some minor bug fixes
- Created a single source and executable for both NT 4 and NT 2000
DownloadsDownload source and precompiled executable - 94 Kb
Download precompiled executable only - 28 Kb