CBFS Disk 2022 .NET Edition
Version 22.0 [Build 8462]


Welcome to CBFS Disk, an easy-to-use toolkit for creating virtual disks whose contents are stored as contiguous blocks of data.

Included Libraries

The .NET Edition includes several libraries (.dll files) which are supported in different environments. The following libraries are present in the lib directory after installation:

Library Supported Runtimes Comments
lib\callback.CBFSDisk.dll .NET Framework 4.0 and up

This is the default library which maintains a familiar API in line with previous versions of the product.

lib\netstandard2.0\callback.CBFSDisk.dll .NET Standard 2.0 and up The .NET Standard library maintains the same API as the default library and can be used in projects that are based on .NET Core and .NET 5 and later.
lib\net20\callback.CBFSDisk.dll .NET Framework 2.0 and up This library targets .NET Framework 2.0 and is maintained for legacy projects.

Included Components

CBDiskThe CBDisk component lets applications create a virtual disk backed by a contiguous block of data.

Additional Information

You will always find the latest information about CBFS Disk at our web site: www.callback.com. We offer free, fully-functional 30-day trials for all of our products, and our technical support staff are happy to answer any questions you may have during your evaluation.

Please direct all technical questions to support@callback.com. To help support technicians assist you as quickly as possible, please provide an detailed and accurate description of your problem, the results you expected, and the results that you received while using our product. For questions about licensing and pricing, and all other general inquiries, please contact sales@callback.com.

Thank You!

Thank you for choosing CBFS Disk for your development needs. We realize that you have a choice among development tools, and that by choosing us you are counting on us to be a key component in your business. We work around the clock to provide you with ongoing enhancements, support, and innovative products; and we will always do our best to exceed your expectations!


The topics in this section provide information regarding the deployment of applications built with CBFS Disk. The information in these topics should be reviewed carefully when designing a deployment strategy, since CBFS Disk's kernel mode drivers and other supplementary DLLs must be distributed along with the application in order for it to function correctly.


Driver Installation

At a high level, CBFS Disk consists of a kernel mode driver, a helper DLL, and a user mode library; all of which work together in tandem to provide the product's functionality. Therefore, it is necessary to install the CBFS Disk kernel mode driver and helper DLL when deploying an application built with the CBFS Disk user mode library.

The functionality needed to install the above-mentioned modules is included in the user mode library itself, as well as in a separate installer DLL. The drivers directory, located within the product's installation directory, contains the following files:

{ComponentName}.cab Contains the main drivers, PnP bus drivers, helper DLLs, and the supplementary installation/uninstallation files.
installer/{ComponentName}Inst.h A header file for the installer DLL. The installer DLL may be used on the target system to install (or uninstall) the items within {ComponentName}.cab.
installer/x64/{ComponentName}Inst.dll The C/C++ installer DLL for the x64 (AMD64) processor architecture.
installer/x86/{ComponentName}Inst.dll The C/C++ installer DLL for 32-bit x86 processor architecture.
installer/ARM/{ComponentName}Inst.dll The C/C++ installer DLL for 32-bit ARM processor architecture.
installer/ARM64/{ComponentName}Inst.dll The C/C++ installer DLL for 64-bit ARM processor architecture.

Windows: Note: When the user-mode library is installed or updated on end-user systems, it is required to ensure that the kernel-mode drivers already present in the system are updated to match the version of the installed user-mode library.

NuGet Notes

If CBFS Disk is installed using NuGet, the drivers directory described above will be located within NuGet's global-packages directory at the following path (assuming NuGet's global-packages directory has not been changed): %USERPROFILE%\.nuget\packages\callback.cbfsdisk\22.0.xxxx\contentFiles\any\any\drivers.

Installation and Uninstallation via User Mode Library Methods

The component includes the following methods to install and uninstall the required files; please refer to their documentation for more information:

Important: Uninstall must only be used when completely removing the driver. When updating the driver, this method must not be used as it may cause the OS to incorrectly remove the driver on reboot. Please refer to the "Updating the Driver" section, below, for more information.

Installation and Uninstallation via Installer DLL Functions

The installer DLL is a lightweight, stand-alone library that contains only the functionality required for installing and uninstalling the required files. It is available in both 32-bit and 64-bit versions (each of which is capable of installing both 32-bit and 64-bit drivers and helper DLLs); and may be used as desired in installation scripts, setup applications, or any other executable capable of loading dynamically-linked libraries (DLLs).

The functions exposed by the installer DLL mirror the component methods listed above. Each function is available in two forms: those with an *A suffix, which can be used with ANSI/UTF8 strings; and those with a *W suffix, which can be used with Unicode (UTF16) strings.

Updating the Driver

To update the driver, call the Install method. The new version of the driver will replace the older version. Please do not call the Uninstall method when updating the driver.

Uninstalling the Driver

To uninstall the driver completely, call the Uninstall method. If the driver cannot be immediately uninstalled, it will be marked for removal and uninstalled on the next reboot.

Use caution when calling Uninstall ; if it gets called and the driver cannot be uninstalled immediately, and then Install is subsequently called to install a new version, then upon reboot, the OS will end up uninstalling the newly-installed driver.

Important: The driver should only be uninstalled when the intent is to completely remove it from the system. Do not uninstall the driver to update it.

Reboot Requirements

Depending on the current state of the system, as well as the options chosen when installing or uninstalling the driver, the OS may need to reboot to complete the operation.

For example, the helper DLL must be loaded by Windows Explorer when it starts, and a reboot or restart of Explorer is required for this to occur. When installing or uninstalling the Plug-and-Play (PnP) drivers, a reboot is almost always requested by Windows.

Always check the return value of the Install and Uninstall methods/functions; it will indicate whether a reboot is required (and if so, which module(s) required it).

Additional Notes

The OS treats major versions of the driver as separate products; they can operate in parallel and do not share any resources. Old major versions may optionally be removed from the system when calling Install by passing the appropriate value for its Flags parameter.

For each major version of the product, only one copy of the driver can be installed at any time. When the driver is being installed, its version is checked, and one of the following three things occurs:

  • If no driver with the same major version is currently installed, then the install procedure installs the driver as a new product.
  • If a driver with the same major version and an older minor version is currently installed, then the install procedure updates the existing driver with the new one.
  • If a driver with the same major version and a newer minor version is currently installed, then the install procedure leaves the existing driver unchanged.

When deploying files to a target system, the CAB file must remain present on the system. This file is required for uninstallation of the driver at a later time.

The product's installation code maintains a ProductGUID-based record of driver installations in the Windows Registry, creating a separate registry entry for each different ProductGUID. When the driver is "uninstalled", the corresponding registry entry is removed. The driver is only removed from the system if there are no entries left in the registry that reference the driver.

Windows 7 and Windows 2008 Server R2

Kernel-mode drivers are signed using the SHA2 algorithm. The original releases of Windows 7 and Windows 2008 Server R2 didn't support SHA2. To be able to load the newest versions of the drivers, the system needs to have certain updates installed. The updates are KB976932 (Service Pack 1 of the mentioned systems) and KB4474419 (Security Update).

Required Permissions

By default, Windows only allows installation and uninstallation of the CBFS Disk system files (kernel mode drivers and helper DLLs) to be performed from a user account which is a member of the Administrators group.

On systems where UAC is enabled, the process responsible for installing or uninstalling the system files must run with elevated permissions. Detection of current privileges and elevation of permissions is not within the scope of the component itself.

Some examples of obtaining the required permissions for driver installation and uninstallation are below.

  • Starting the application which uses the component with the "Run as administrator" option.
  • Modifying the Load and unload device drivers setting in the Local Security Policy under the User Rights Assignment section.
  • Including a manifest alongside the application indicating the requirement for elevated permissions. For instance, if a file MyApp.exe.manifest with the content below exists next to the application MyApp.exe, it will prompt for elevated permissions when started (if required).

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0"> <assemblyIdentity version="" processorArchitecture="X86" name="ExeName" type="win32"/> <description>elevate execution level</description> <trustInfo xmlns="urn:schemas-microsoft-com:asm.v2"> <security> <requestedPrivileges> <requestedExecutionLevel level="requireAdministrator" uiAccess="false"/> </requestedPrivileges> </security> </trustInfo> </assembly>

User Mode API

Windows: Note : The user-mode library must be deployed to end-user systems together with the kernel-mode drivers; the version of the kernel-mode drivers on the end-user systems must be equal or newer to the version of the user-mode library. Thus, when the user-mode library is installed or updated on end-user systems, it is required to ensure that the kernel-mode drivers already present in the system are updated to match the version of the installed user-mode library.

The user mode library comes in two pieces, both of which must be deployed along with the application:

  1. A .NET assembly (managed), named callback.cbfsdisk.dll (or callback.cbfsdisk.NetStd.dll, for .NET Standard).
  2. A native dynamic library (unmanaged), named cbfsdisk22.dll, available for both 32-bit (x86) and 64-bit (x64, ARM64) processor architectures.

When deploying the application, copy both the .NET assembly and the native library to the target system and place them next to the application's executable file, (on Windows, it has the .exe extension).

Windows Only:

The .NET assembly may alternatively be deployed to the Global Assembly Cache (GAC).

Alternatively, the native dynamic library may be placed into one of directories, pathes to which are contained in the

  • Windows: PATH environment variable, such as C:\Windows\System32 (or C:\Windows\SysWOW64 when deploying a 32-bit application on a 64-bit Windows system)
  • Linux: LD_LIBRARY_PATH environment variable
  • macOS: DYLD_LIBRARY_PATH environment variable

NuGet Notes

After the NuGet package is added to a project, both the managed .NET assembly and the unmanaged native library will be copied to the project's output directory anytime the project is built. However, the exact files copied to the output directory for the native library will vary based on the project type:

  • For .NET Core projects, a runtimes directory will be created in the output directory (if it does not already exist), and versions of the native library for each supported runtime identifer (RID) (e.g., win-x64) will be placed in the appropriate subdirectories. When the .NET Core application is distributed, the entire runtimes directory should be deployed alongside it.
  • For other types of projects (.NET Framework, UWP), only the native library version specific to the currently-selected platform target (e.g., x64) will be copied to the output directory.
    • For .NET Framework projects specifically, please note that the project's platform target (Project > Properties > Build Tab > Platform target) must be set to a real architecture. If it is set to "Any CPU", no native library will be copied to the output directory.


The native library may alternatively be installed to the Windows System directory. This approach allows deploying both the 32-bit and 64-bit versions of the native library simultaneously, since each gets placed into the system directory that corresponds to the appropriate processor architecture.

Windows Only: Remember to deploy the drivers too, as they are an integral part of CBFS Disk.

General Information

The topics in this section provide general information about various aspects of the product's functionality.


Custom Drive Icons

Virtual drives created with the CBDisk component can have a custom icon associated with them to better distinguish them in Windows Explorer. There are a few different ways to accomplish this:

Using Additional Files

If placing additional files into the virtual drive itself is an acceptable condition, Windows provides a couple of file-based mechanisms for specifying a custom icon.

To specify a custom icon for the virtual drive itself, an autorun.inf file can be created based on the information in Microsoft's Autorun.inf article.

Additionally, custom icons can be specified for subdirectories of the virtual drive using desktop.ini files, which can be created based on the information in Microsoft's Desktop.ini article. Note that desktop.ini files cannot be used to specify a custom icon for the root directory of the virtual drive (i.e., they cannot be used to change the icon of the virtual drive itself).

Using Registry Keys

If the virtual drive is assigned a persistent drive letter, using registry keys to assign a custom icon may be a good option. To specify a custom icon using the registry, create a subkey like {DriveLetter}\DefaultIcon (e.g., K\DefaultIcon) under one of the following keys:

  • HKEY_CURRENT_USER\SOFTWARE\Classes\Applications\Explorer.exe\Drives, if the custom icon should only be used for the current user.
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\DriveIcons, if the custom icon should be used for all users. (Note that manipulating anything under the HKEY_LOCAL_MACHINE registry hive requires administrative rights.)

Regardless of which key it is created under, the {DriveLetter}\DefaultIcon subkey's (Default) (i.e., "unnamed") value should then be set to the absolute path of the icon file.

Please note that custom icons specified in this manner are only effective so long as the drive letter assigned to the virtual drive remains unchanged over time; if its drive letter changes, the registry keys used to specify the custom icon will need to be updated accordingly.

Using the Component and its Shell Helper DLL

As long as the Helper DLL has been installed to the system using the Install method, custom icons can be assigned to a virtual drive directly using the component. This method of specifying custom icons is especially valuable when project constraints preclude placing additional files into the drive or modifying the registry.

Custom icons assigned in this manner function a bit differently than those assigned using the two methods described above, as they are implemented using Windows' icon overlay mechanism. Consequently, the custom icons are restricted to 25% of the original icon's area (except for 16x16 icons); the tables below describe the required sizes and color levels of the assets in the icon file.

Overlay icon sizes map as follows:

Main Icon SizeOverlay Icon Size

Icon assets must have the following color levels:

Icon SizeColor Level
16x1616 colors
32x3216 colors
48x48256 colors
256x25632-bit color

Because it's possible to specify multiple different overlay icons (e.g., to represent different drive states), icons are assigned through the component using a two-step process:

  1. Register the desired icon(s) using the RegisterIcon method. (Note that administrative rights are required to execute this method successfully.)
  2. Switch between the registered icon(s) using the SetIcon and ResetIcon methods.

Icons are copied to a temporary location when registered; and removed from said location when unregistered using the UnregisterIcon method.

It is important to keep in mind that Windows limits the number of registered overlay icons to 15 (this is a global limit for the entire system, and it cannot be changed). Since other applications on the system (e.g., OneDrive, Dropbox, etc.) may have registered multiple overlay icons, it's not uncommon to get into a situation where various applications are competing to have their overlay icons registered.

Overlay icons are registered by placing values in the following keys in the Registry:

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\ShellIconOverlayIdentifiers
  • HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\explorer\ShellIconOverlayIdentifiers (64-bit Windows only)
If necessary, it's up to the application (or better yet, the user) to decide whether or not to remove other entries; however, doing so too aggressively will likely have a negative impact on the user's experience with other applications.

Error Reporting and Handling

Error Codes

The CBFS Disk communicates errors using the Win32 error codes defined in WinError.h, which is part of the Windows Platform SDK. The CBFS Disk system drivers, however, use NT native error codes, which don't have one-to-one mappings with Win32 error codes. The component includes logic for converting between the two as necessary, and that logic can be updated if there are any codes that are not covered.

Additionally, there are certain error codes which CBFS Disk uses use in a special manner. For more information about such error codes, please refer to the Error Codes page.

Reporting Errors to the Component from Event Handlers

If the event has a ResultCode parameter, the event handler can use it to return the result code of the operation to the component. The ResultCode parameter is set to 0 by default, which indicates the operation was successful.

If an unhandled exception occurs in the event handler, it will be caught by the component, which will fire the OnError event.

In some events, the OS doesn't expect the error code to be returned and either the component or the OS ignores the returned error code. Please, refer to the description of a particular event for more information.

How to Handle Errors Reported by the Component

If an error occurs, the component will throw an exception. The Code property of the exception object will contain an error code, and the Message property will contain an error message (if available).

Extended Logging in Windows

Some component methods in CBFS Disk are capable of writing extended information about reported errors to the Windows event logs, which can be viewed using the system's eventvwr.exe tool. The user mode part of the component writes to the "Windows Logs \ Application" folder, while the kernel mode part writes to the "Windows Logs \ System" folder.

The information written in the extended logs is meaningful to the Callback Technologies development team, but not to end-users, so extended logging is disabled by default. If issues occur during the installation of the CBFS Disk system drivers, or while using the component, please do the following:

  1. Enable extended logging (see below).
  2. Replicate the issue.
  3. Using Event Viewer (eventvwr.exe), export the event log entries from the locations mentioned above in native format (please restrict the scope of the export to just those entries related to CBFS Disk).
  4. Submit an issue report that includes the exported file.

There are two ways to toggle extended logging for a component:

  1. By toggling the component's LoggingEnabled configuration setting.
  2. By adding a DWORD-typed value named Enabled to the HKEY_LOCAL_MACHINE\SOFTWARE\Callback Technologies\{ComponentName}\EventLog registry key and setting it to 0 (disabled) or 1 (enabled).
    • Replace the {ComponentName} part of the registry key path with the name of the applicable component.
    • If this registry key, one of its parents, or the value itself does not exist, please create it manually.
    Note that if your code runs in emulated mode (x86 mode on x64 or ARM64 architecture), you need to add the value to the HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Callback Technologies\{ComponentName}\EventLog registry key in addition to the "main" registry key.

The system must be rebooted anytime extended logging is enabled or disabled to make the changes take effect.

Event Handling

The topics in this section provide information about event handling.


Buffer Parameters

Some events include one or more parameters intended for use as a binary data buffer. Depending on the event, these parameters may contain data when the event is fired, or it may be expected that the application populates them with the desired amount of data during the event handler. Some events combine both paradigms, and expect the application to modify the data already present when the event is fired.

The documentation for such events will describe which of the above cases applies to each buffer parameter. Note that, in all cases, buffer parameters point to a pre-allocated block of unmanaged memory, the size of which is specified by the parameter immediately following the buffer parameter. In cases where data is to be written, be sure to write it directly to the pointed-to memory, don't change the value of the buffer parameter itself.

Buffer parameters are always of the IntPtr type; use the .NET Marshal.Copy() method to read and write data from and to the unmanaged memory region. When targeting newer .NET versions, such as .NET Standard 2.1 and later, applications can use the Span<T> and ReadOnlySpan<T> classes to access and modify the unmanaged memory region without extra data copying.

Recursive Calls

To ensure stable operation, it is critical to avoid accessing drives and filesystems recursively. Essentially, this means that event handlers must not perform any operations involving the drive or filesystem that the event fired for (i.e., don't read from/write to files on it, don't unmount the media, etc.).


Because the component's events are typically tied directly to requests from the OS itself, it is critical that event handlers complete requests quickly to prevent the system from being blocked. To help prevent such blocking, the CBFS Disk system driver can enforce request timeouts on a per-virtual-drive basis.

A virtual drive's request timeout interval is specified by passing the desired number of milliseconds to the Timeout parameter when calling the MountMedia method. The value passed to the Timeout parameter must either be a positive value greater than or equal to 3000, or 0, indicating that timeouts should not be enforced, in which case events may take as long as necessary to execute.

When timeout enforcement is in effect, and an event executes long enough for its timeout to expire, the driver cancels the underlying request by reporting an error to the OS. The tardy event still runs to completion, but any results it returns once finished are ignored because the underlying request has already been handled.

Applications should always strive to ensure that all event handlers complete quickly, even if request timeouts are disabled. Do not perform time-consuming work, especially network operations, within event handlers; offload such work to background threads. For example, a viable strategy for writing to a remote file would be to pass the data to be written to a background thread, and then to immediately finish the event handler. Similarly, to read from a remote file, an application could pre-cache some of its data with the help of a worker thread, and then return the cached data when requested.

Helper DLL

The Helper DLL is integrated into Windows Explorer and offers functionality designed to provide users with a consistent and pleasant experience. It is recommended that the Helper DLL be installed alongside the system driver, which can be accomplished by including the MODULE_HELPER_DLL flag when calling the Install method.

The Helper DLL is distributed in the same .cab file as the system driver; its name is CBDiskShellHelper22.dll, and it is shipped in both 32-bit and 64-bit variants. Its functionality is described below.

Mounting Point Change Broadcasts

Anytime a mounting point is added or removed, the system driver will send a notification to the Helper DLL, which then broadcasts a system message instructing Windows Explorer to refresh the list of drives. Without this functionality, Windows Explorer will not refresh the list of drives if a mounting point is added or removed from a Windows service or another user session.

Network Mounting Point

When a network mounting point is used, the Helper DLL provides the functionality that allows Windows Explorer to correctly display the current status of, and interact with, the virtual drive. Without this functionality, the virtual drive will display as "Disconnected", which may result in unexpected behavior.

Custom Icons

When custom icons are used for a virtual drive, the Helper DLL ensures that they are properly displayed in Windows Explorer.

Mounting Points

A mounting point is a name that can be used to access a volume. When the filesystem driver mounts a volume, it must make that volume accessible by creating one or more mounting points for it.


Mounting points can be global (visible in all user sessions) or local (visible only to a specific user session). The AddMountingPoint method creates global mounting points by default; applications must include the STGMP_LOCAL flag in the Flags parameter value to create local mounting points. (Note: The STGMP_MOUNT_MANAGER flag is not compatible with the STGMP_LOCAL flag.)

When creating a local mounting point, applications can specify a specific user session for it to be visible in by passing that session's Authentication ID for the AuthenticationId parameter (retrieval of Authentication IDs is discussed in a later section). If no Authentication ID is provided (i.e., 0 is passed), the local mounting point is created in the current user session; and if the application does this while running with elevated rights, then the local mounting point will only be visible in the elevated session, and consequently won't be available to applications in other sessions (such as, e.g., Windows Explorer).

When mounting points are added or removed, a system message (WM_DEVICECHANGE) is broadcast. It instructs Windows Explorer to refresh the list of drives available. However, these messages cannot cross user session boundaries; so if, for example, the application is running as a service, Windows Explorer may not receive the broadcast and thus fail to refresh the list of drives. To address this issue, CBFS Disk includes a Helper DLL which, among other things, helps ensure that Windows Explorer always refreshes the list of drives regardless of which user session the application is running in; please refer to that topic for more information.

Types of Mounting Points

There are a handful of different mounting point types, each of which exposes volumes in a slightly different manner:

  • Drive letter mounting points
  • Folder mounting points
  • Network mounting points
  • UNC path mounting points

Each type of mounting point is discussed in more detail below.

Drive Letter Mounting Points

Drive letter mounting points are one of the more commonly-used mounting point types thanks to users' familiarity with them. To create a drive letter mounting point, pass a string composed of a single character in the A-Z range followed by a colon (e.g., Z:) for the AddMountingPoint method's MountingPoint parameter.

If the value passed for the AddMountingPoint method's Flags parameter includes the STGMP_AUTOCREATE_DRIVE_LETTER flag, the component will assign a drive letter automatically. In this case, the value passed for the MountingPoint parameter must not include a drive letter.

Folder Mounting Points

A folder mounting point makes a volume accessible through a folder located on another (pre-existing) NTFS volume. Folder mounting points are always visible to all users in the system, and their creation requires administrative privileges.

To create a folder mounting point using the AddMountingPoint method, include the STGMP_MOUNT_MANAGER flag in the Flags parameter , and pass the target folder's absolute path for the MountingPoint parameter (e.g., C:\MountedDrives\MyMountingPoint). The target folder must already exist, must reside on an NTFS volume, and must be empty; otherwise, the call will fail.

Authentication IDs

An Authentication ID is a locally unique identifier (LUID) assigned to a logon session (or, "user session"), retrievable through the access token that represents said session. Applications can obtain the Authentication ID of a session from an access token or by enumerating logon sessions.

To obtain an Authentication ID from an access token, call the Windows API's GetTokenInformation function and pass either TokenGroupsAndPrivileges or TokenStatistics for the TokenInformation parameter. The resulting value will be a reference to a structure (TOKEN_GROUPS_AND_PRIVILEGES or TOKEN_STATISTICS, respectively) containing the needed Authentication ID.

To enumerate logon sessions, use the Windows API's LsaEnumerateLogonSessions function, which returns a list of existing logon session IDs (that is, Authentication IDs). To obtain additional information about a particular logon session (e.g., in order to determine if it's the desired one), use the Windows API's LsaGetLogonSessionData function. Network Mounting Points

Network mounting points are similar to other mounting point types, except that the system treats them as "remote devices". This distinction is useful since:

  • Windows Explorer makes fewer requests for files located on remote devices.
  • Some applications are more tolerant of timeouts and delays when working with remote devices.

Therefore, when an application is designed to work with some slow or remote storage medium, it's recommended that it use a network mounting point. When using network mounting points, it's important that the Helper DLL be used so that Windows Explorer displays the correct drive status.

To create a network mounting point using the AddMountingPoint method, include the STGMP_NETWORK flag in the Flags parameter, and pass a string of the form <Local Name>;<Server Name>;<Share Name> for the MountingPoint parameter.

  • <Local Name> is the name to use for the mounting point on the local system; it can be a drive letter or a name for use in a UNC path. Alternatively, it can be left empty, in which case the volume will only be accessible via the network path (see below) or the drive letter will be assigned automatically if the STGMP_AUTOCREATE_DRIVE_LETTER flag is used.
    • Note: This "local name" is not related to the concept of "local and global mounting points" discussed in the overview.
  • <Server Name> and <Share Name> are used to create a network path of the form \\<Server Name>\<Share Name>. This network path is not shared by default (see notes following examples below).

The set of characters allowed in server names, is defined in this document. The set of characters allowed in share names, is defined in this document.

With the above information in mind, here are some examples of valid MountingPoint parameter values when creating network mounting points:

  • Y:;MyServer;VirtualShare: Creates a network mounting point accessible both via the drive letter Y: and via the network path \\MyServer\VirtualShare.
  • MyMountingPoint;MyServer;VirtualShare: Creates a network mounting point accessible both via the UNC path \\.\MyMountingPoint and via the network path \\MyServer\VirtualShare
  • ;MyServer;VirtualShare: Creates a network mounting point accessible only via the network path \\MyServer\VirtualShare.

As stated above, the network paths created for network mounting points are not shared (i.e., visible to other computers on the network) by default. To have the component create an actual network share when AddMountingPoint is called, applications must include either the STGMP_NETWORK_READ_ACCESS or the STGMP_NETWORK_WRITE_ACCESS flag in the Flags parameter value, and use empty string for the <Server Name> segment of the MountingPoint parameter value (the local computer's name is used). Note that when the mounting point is shared in this way, a local resource is created and then shared. The name of the resource is derived from the Share Name defined above. However, the set of allowed characters for such name is not strictly defined. Additionally, sharing is done using a call to NetShareAdd Windows API function, which can be called by Administrators, System Operators, and Power Users.

UNC Path Mounting Points

UNC path mounting points make a volume available via a specific name, and unlike other mounting points types, they are not displayed anywhere in Windows Explorer; the UNC path must already be known.

UNC path mounting points consist of the \\.\ prefix, followed by a name (e.g., \\.\CBDrive1). The mounting-point-related component methods expect just the name (i.e., the UNC path with the \\.\ prefix omitted). So to add a new UNC path mounting point like, e.g., \\.\CBDrive1, call the AddMountingPoint method and pass CBDrive1 for the MountingPoint parameter.

Linux and macOS:

A virtual drive / filesystem is mounted to a directory, which must exist at the time of mounting and be empty; otherwise, the call will fail.


Note: The below information applies to the operations of the component on Windows .

CBFS Disk is a complex product that operates in both user mode and kernel mode simultaneously; so when a serious issue occurs, it's critical that we are able to obtain sufficient information about the circumstances of the failure.

In order to help us assist you in a more expedient manner, please collect the information described in the instructions below when reporting a serious issue (i.e., one that causes the system to crash or hang). Our development team cannot effectively diagnose such issues without this information.

Also, please note that these sorts of issues commonly involve environmental differences and other factors that are either unforeseen or otherwise out of our control. It is also not unheard-of for a crash to appear attributable to one thing while in fact being caused by something completely different. Rest assured that we are committed to assisting you as best we can, and we thank you ahead-of-time for your patience and understanding throughout the support process.

System Crashes (BSODs)

If you encounter a consistently-reproducible system crash (BSOD) that you suspect may be due to CBFS Disk, please obtain a crash dump and include it when reporting the issue to us. Our development team is unable to diagnose system crashes without the information these dumps contain.

Ensure that your system is set up to generate crash dumps, and to not restart automatically after a crash, by following the steps found in Microsoft's Enabling a Kernel-Mode Dump File article. The options available in the memory dump dropdown vary depending on your version of Windows; please choose the first one from the following list that is present in yours:

  • Complete
  • Full
  • Automatic
  • Kernel

Once your system is set up to generate crash dumps, perform the same action that caused the BSOD originally to trigger the crash again. When it occurs, be sure to copy the information on the BSOD screen exactly so that it can be included in your submission (a picture of the screen in which all of the information is legible is also acceptable). Here are some examples of the specific information we're looking for:

Recent versions of Windows:

What failed: cbfs***22.sys Stop Code: FILE_SYSTEM

Older versions of Windows:

STOP: 0x00000022 (0x00240076, 0xF7A07AA8, 0xF7A077A8, 0xF7800C82) cbfs***22.sys - Address F7800C82 base at F77CD000, DateStamp 447d6975

After you've copied this information, reboot and check that the memory dump file was created at %SYSTEMROOT%\MEMORY.DMP (typically this is C:\Windows\MEMORY.DMP; if you changed the dump file location in the crash dump settings, check the location you specified instead). It will be a very large file that is too big to attach to an email, so please upload it to a file sharing site of your choice and generate a sharing link that our development team can use to download it.

Finally, submit a support issue to us that includes the link to your dump file, all of the information from the BSOD screen (if you took a picture, attach it or provide another sharing link), a description of how the BSOD was triggered, and any other information that you feel is relevant.

System Hangs

If you encounter a consistently-reproducible system hang that you suspect may be due to CBFS Disk, you'll need to collect the same information as described above. But in order to obtain a crash dump, you'll first need to configure your system so that you can trigger a crash from the keyboard once it hangs. To make this possible, follow these steps (adapted from Microsoft's Forcing a System Crash from the Keyboard article):

  1. First, using the instructions provided in the section above, configure your system to generate crash dumps, and to not restart automatically after a crash.
  2. Next, you must enable keyboard-initiated crashes in the registry by creating a new value named CrashOnCtrlScroll, and setting it equal to a REG_DWORD value of 0x01, in all of the following registry keys:
    • HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\i8042prt\Parameters
    • HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\kbdhid\Parameters
    • HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\hyperkbd\Parameters
  3. Finally, you must restart the system in order for these settings to take effect.

After these steps are complete, you'll be able to trigger a keyboard-initiated crash by using the following hotkey sequence: hold down the Right CTRL key, and press the SCROLL LOCK key twice.

At this point, you can perform the same action that caused the system to hang originally to trigger the hang again. Once the system hangs, use the hotkey sequence to force it to crash, and then follow the rest of the instructions from the section above to collect and submit the necessary information.

Application Crashes

Sometimes, an application crashes while the OS continues to operate, and the name of one of the modules of CBFS Disk is present in the crash information. A crashing application can be the one that uses CBFS Disk or some third-party process. If the crash occurs repeatedly, it is possible to make use of a User-Mode Crash Dump to locate or narrow down the source of the crash. Generation of crash dumps is disabled by default. Before you reproduce the crash, you need to Enable Collecting User-Mode Crash Dumps.

After you enable the crash dump, you don't need to reboot, you can proceed to reproduction of the crash immediately. After the crash re-occurs, you can pick the dump file from its location. The default locations of user-mode dump files are:

  • For regular applications: %LOCALAPPDATA%\CrashDumps
  • For System services: %WINDIR%\System32\Config\SystemProfile
  • For Network and Local services: %WINDIR%\ServiceProfiles
If you changed the dump file location in the crash dump settings in the Registry, check the location you specified instead.

A crash dump can be a large file (depending on the settings) that is too big to attach to an email, so please upload it to a file sharing site of your choice and generate a sharing link that our development team can use to download it.

Finally, submit a support issue to us that includes the link to your dump file, a description of how the BSOD or a manual crash was triggered, and any other information that you feel is relevant.


All constants are accessible through the callback.CBFSDisk.Constants class.

Module Flags

MODULE_PNP_BUS 0x00000001 PnP Bus Driver (.sys file).

This module must be installed if the application wishes to make use of Plug-and-Play (PnP) storage features. PnP storage devices are those visible as disks in the Device Manager, and the system treats such storage devices differently from other purely virtual devices.

The filesystem driver must be reinstalled any time this module is added or removed.

MODULE_DRIVER 0x00000002 Core Product Driver (.sys file).

The product's filesystem driver module provides the core of its functionality; it must be installed for the product to function correctly.

MODULE_HELPER_DLL 0x00010000 Shell Helper DLL (CBDiskShellHelper22.dll)

This module provides supplementary functionality; please refer to the Helper DLL topic for more information.

Note: This module is not applicable when calling the GetDriverStatus method.

Install Flags

INSTALL_REMOVE_OLD_VERSIONS 0x00000001 Uninstall drivers and helper DLLs from previous component versions (e.g., 2017).

INSTALL_KEEP_START_TYPE 0x00000002 Keep the driver's current start type setting in the registry.

If this flag is not set (default), the installation logic will reset the driver's start type setting in the Windows registry to the default value. Setting this flag causes the installation logic to preserve the current value, which may be necessary if the user (or the application itself) set it previously.

INSTALL_OVERWRITE_SAME_VERSION 0x00000004 Install files when their version is the same as the version of already installed files.

If this flag is not set (default), the installation logic will overwrite the existing file only if the version number of the file being installed is larger than the version of the file being overwritten. Setting this flag causes the installation logic to overwrite the file even when it has the same version.

Uninstall Version Flags

UNINSTALL_VERSION_PREVIOUS 0x00000001 Uninstall modules from previous product versions.

UNINSTALL_VERSION_CURRENT 0x00000002 Uninstall modules from the current product version.

UNINSTALL_VERSION_ALL 0x00000003 Uninstall modules from all product versions.

Module Status Flags

MODULE_STATUS_NOT_PRESENT 0x00000000 The specified module is not present on the system.

MODULE_STATUS_STOPPED 0x00000001 The specified module is in the Stopped state.

MODULE_STATUS_RUNNING 0x00000004 The specified module is loaded and running.

Mounting Point Flags

STGMP_SIMPLE 0x00010000 Create a simple mounting point.

Simple mounting points may be local or global; and when local, can be made visible in either the current user session or another one.

This flag cannot be combined with STGMP_MOUNT_MANAGER or STGMP_NETWORK, and is implied if neither of those flags are present.

STGMP_MOUNT_MANAGER 0x00020000 Create a mounting point that appears to the system as a physical device.

When the StorageType property is set to STGT_DISK_PNP, mounting points created using the system mount manager appear as physical devices in the Disk Management snap-in of the Microsoft Management Console (mmc.exe).

This flag is a necessary prerequisite for creating a folder mounting point, which makes a drive accessible via an otherwise empty directory on another NTFS volume.

This flag cannot be combined with STGMP_SIMPLE, STGMP_NETWORK, or STGMP_LOCAL.

Only one mounting point of this type can be added to a virtual drive.

STGMP_NETWORK 0x00040000 Create a network mounting point.

Network mounting points can be further configured using the various STGMP_NETWORK_* flags described below. Applications that plan to make use of network mounting points must be sure to install the Helper DLL before doing so, otherwise Windows Explorer will not correctly recognize the "network" drive.

This flag cannot be combined with STGMP_SIMPLE or STGMP_MOUNT_MANAGER.

STGMP_LOCAL 0x10000000 Specifies that a local mounting point should be created.

This flag specifies that a local mounting point should be created rather than a global one. When this flag is set, applications must also pass an appropriate value for the AddMountingPoint method's AuthenticationId parameter.

Passing 0 for AuthenticationId will make the mounting point visible in the current user session. To make the mounting point visible in a different user session instead, pass the target session's Authentication ID.

This flag is valid when combined with STGMP_SIMPLE or STGMP_NETWORK; it cannot be combined with STGMP_MOUNT_MANAGER. Please note that a mounting point can be made available to other computers as a network share, and network shares are always globally visible on the local machine, even if this flag is set.

STGMP_NETWORK_ALLOW_MAP_AS_DRIVE 0x00000001 Indicates that users may assign a drive letter to the share (e.g., using the 'Map network drive...' context menu item in Windows Explorer).

STGMP_NETWORK_HIDDEN_SHARE 0x00000002 Indicates that the share should be skipped during enumeration.

Such shares are only accessible when their name is already known to the accessor.

STGMP_NETWORK_READ_ACCESS 0x00000004 Makes a read-only share available for the mounting point.

When this flag is specified, the <Server Name> part of the MountingPoint parameter value must be empty. Please refer to the Mounting Points topic for more information. This flag makes the component use the Windows API's NetShareAdd function. As per MSDN, "Only members of the Administrators, System Operators, or Power Users local group can add file shares with a call to the NetShareAdd function."

STGMP_NETWORK_WRITE_ACCESS 0x00000008 Makes a read/write share available for the mounting point.

When this flag is specified, the <Server Name> part of the MountingPoint parameter value must be empty. Please refer to the Mounting Points topic for more information. This flag makes the component use the Windows API's NetShareAdd function. As per MSDN, "Only members of the Administrators, System Operators, or Power Users local group can add file shares with a call to the NetShareAdd function."

STGMP_NETWORK_CLAIM_SERVER_NAME 0x00000010 Specifies that the server name is unique.

When this flag is specified, the driver handles IOCTL_REDIR_QUERY_PATH[_EX] requests by instructing the OS to direct all requests going to the <Server Name> part of the MountingPoint parameter's value to the driver instead.

This flag should be used when the <Server Name> is unique within the local system (e.g., when the application's name is used). Using this flag allows the system to avoid delays caused by certain network requests made by various processes.

This flag is also required for "net view" command to be able to show the share in the list.
STGMP_DRIVE_LETTER_NOTIFY_ASYNC 0x20000000 Causes the method to return immediately without waiting for mounting notifications to be sent to the system.

STGMP_AUTOCREATE_DRIVE_LETTER 0x40000000 Tells the component that it should assign the drive letter automatically.

When this flag is specified, the component will automatically assign a drive letter from the list of available letters. The assigned letter is added to the end of the list of mounting points, and can be retrieved from there.

Do not include a drive letter in the MountingPoint parameter's value when specifying this flag.

Storage Type Values

STGT_DISK 0x00000000 Create a regular disk device.

STGT_CDROM 0x00000001 Create a CD-ROM or DVD device.

STGT_DISK_PNP 0x00000003 Create a plug-and-play storage device.

Important: The CBFS Disk system driver must be installed in PnP mode for this option to function properly.

Storage Characteristics Flags

STGC_FLOPPY_DISKETTE 0x00000001 The storage is a floppy disk device.

This flag is not supported when StorageType is set to STGT_DISK_PNP.

STGC_READONLY_DEVICE 0x00000002 The storage is a read-only device.

STGC_WRITE_ONCE_MEDIA 0x00000008 The storage device's media can only be written to once.

This flag is not supported when StorageType is set to STGT_DISK_PNP.

STGC_REMOVABLE_MEDIA 0x00000010 The storage device's media is removable.

Users may remove the storage media from the virtual drive at any time. (Note that this flag does not indicate that the virtual drive itself is removable.)

STGC_AUTOCREATE_DRIVE_LETTER 0x00002000 The system should automatically create a drive letter for the storage device.

Deprecated: Include the STGMP_AUTOCREATE_DRIVE_LETTER flag in the value passed for the AddMountingPoint method's Flags parameter instead.

When this flag is present, the StorageGUID property must be set. This flag only works when StorageType is set to STGT_DISK_PNP.

STGC_SHOW_IN_EJECTION_TRAY 0x00004000 The storage device should be shown in the 'Safely Remove Hardware and Eject Media' menu in the system notification area (system tray).

This flag only works when StorageType is set to STGT_DISK_PNP.

STGC_ALLOW_EJECTION 0x00008000 The storage device can be ejected.

Users may eject the virtual drive at any time. When the virtual drive is ejected, it is destroyed.

This flag only works when StorageType is set to STGT_DISK_PNP.

STGC_RESERVED_1 0x00010000 Reserved, do not use.

STGC_RESERVED_2 0x00020000 Reserved, do not use.

Copyright (c) 2023 Callback Technologies, Inc. - All rights reserved.
CBFS Disk 2022 .NET Edition - Version 22.0 [Build 8462]