What are Reparse Points in Windows 7 and How Do They Work?

In Windows 7, reparse points are a powerful feature of the NTFS file system that allow for advanced file system behavior. These special objects, which are similar to shortcuts, enable a wide range of functionality, from symbolic links and mount points to file system filters and more. Understanding how reparse points work is crucial for anyone working with the Windows file system, whether as an administrator, developer, or power user.

What are Reparse Points?

Reparse points are a type of file system object that can be attached to files or directories. They contain a collection of user-defined data, along with a reparse tag that identifies the type of data stored. When an application or file system filter encounters a reparse point, it can interpret the data and perform specific actions based on its contents.

One of the key features of reparse points is that they can be used to implement symbolic links, which allow you to create a reference to a file or directory that appears to be located in a different place in the file system hierarchy. This can be useful for organizing files, creating shortcuts, or even mapping network drives.

Reparse points can also be used to implement mount points, which allow you to attach a file system volume to a specific location in the file system hierarchy. This can be useful for organizing storage, creating backup volumes, or even implementing virtual file systems.

How Reparse Points Work

When a file or directory with a reparse point is accessed, the file system checks the reparse tag to determine what type of data is stored in the reparse point. If the reparse point is associated with a file system filter, the filter is loaded and given the opportunity to process the file or directory.

For example, if a file with a reparse point is opened, the file system will check the reparse tag to see if there is a file system filter associated with that tag. If a filter is found, the filter is loaded and given the opportunity to process the file. The filter can then perform any necessary operations, such as mapping the file to a different location or performing additional security checks.

Reparse points can also be used to implement file system filters, which allow you to add custom behavior to the file system. For example, you could create a file system filter that automatically compresses or encrypts files based on certain criteria.

Using Reparse Points

Reparse points can be created and managed using a variety of tools, including the Windows command line, PowerShell, and various third-party utilities. For example, you can use the `mklink` command to create symbolic links, or the `mountvol` command to create mount points.

It’s important to note that reparse points are a powerful feature, and they can have unintended consequences if used incorrectly. For example, if you create a symbolic link that points to a location above itself in the file system hierarchy, you can create a cyclic reference that can cause problems for some applications.

Overall, reparse points are a powerful and flexible feature of the Windows file system that allow for advanced file system behavior. Whether you’re an administrator, developer, or power user, understanding how reparse points work and how to use them effectively can be a valuable skill.