![]() ![]() With reasonably good documentation and a significant set of examples on GitHub, many devs feel that writing a file system Minifilter is well within their ability. This is for good reason, because the Minifilter model provides an excellent organization and support framework for file system filter driver development. Since its introduction in Windows XP SP2, the File System Minifilter model has become the preferred mechanism for implementing file system filters. And because file system filters are able to be the first interpreters of the file system “name space” that applications see, they can also perform powerful file redirection operations, such as making a remote file (such as one stored somewhere in the cloud) appear to be local. For example, because they see which files are created and written, file system filters are often play key roles in backup products and hierarchical storage subsystems. File system filters can also be used for other, less obvious, purposes. If no viruses are found, the open request can be allowed to complete normally.įile system filters are commonly used for everything from antivirus and malware scanning as just described, to software license tracking and management, to auditing and changed tracking on files, to on access transparent data encryption and decryption. If any viruses are found, the open request can be canceled. ![]() This type of filter typically intercepts file open requests and suspends them while the filter (or, more likely, an associated service running in user mode) scans the file being opened for viruses. The type of file system filter that most people are familiar with is probably the antivirus filter. This allows them to monitor, track, manage, manipulate, and even accept or reject I/O operations before the file system gets to see them. File system filters intercept I/O operations (from both applications and the system itself) before those I/O operations reach the file system. ![]() One of the most common, and also the most powerful, places to insert a filter in a Windows system is over a file system. And, of course, filtering a device requires no change to the driver for the underlying device. A filter can add value to the functionality of an existing device by simply attaching itself over that device. By intercepting the request before it reaches its intended target, the filter driver can extend or replace functionality provided by the original target of the request.The filter driver concept is one of the most powerful architectural features of the Windows I/O subsystem. An Introduction to Windows File System Filter DriverĪ file system filter driver intercepts requests targeted at a file system or another file system filter driver. ![]()
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