If victorious, the driver can do further initialization as needed and finally call FltStartFiltering to start filtering operations. The driver sets up appropriate structures and then calls the FltRegisterFilter routine to register. The Mini-filter driver must register as a mini-filter with the filter manager, specifying various settings, such as what operations it wishes to intercept. Status = FltStartFiltering( MiniFilterData.Filter ) įltUnregisterFilter( MiniFilterData.Filter ) Status = FltRegisterFilter( DriverObject, Register with FltMgr to tell it our callback routines MiniFilterData.DriverObject = DriverObject KdPrint(( " PocMiniFilter!DriverEntry: Entered\n") ) It is called at IRQL PASSIVE_LEVEL and in the system process context. Thus the DriverEntry will be called first and one time. In NT, only one driver instance is loaded, regardless of the number of devices, the driver will control. The I/O Manager calls a driver's DriverEntry routine when the driver is loaded. For reference, follow the attached source code. You can download the passthrough sample from GitHub, remove non-relevant code, and start writing. In Visual Studio 2019, locate the Create New Project and find the template to use Empty WDM Driver. A filter driver with a low numerical altitude is loaded into the I/O stack below a filter driver with a higher numerical value. The Altitude is an infinite-precision string interpreted as a decimal number. The filter manager receives the IRP, and then the filter manager calls upon the mini-filter it's managing, in descending order of the Altitude. Each Mini-filter has its Altitude, which determines its relative position in the device stack. Windows provide a legacy filter driver called the Filter manager implemented as a legacy filter driver. A Minifilter driver intercepts I/O operations sent between the I/O manager and the file system driver. There exist other types of file systems, such as Physical file systems (UDFS, CDFS, FAT), Network redirectors (RDR, NWRDR, WebDAV), and Special file systems (Npfs, Msfs). The new technology file system (NTFS) is its native file system. What is a File System Mini-filter Driver?įile systems are targets for I/O operations to access files. However, the user can modify the driver to block/allow the device to be connected to any bus. The demo driver block writes for all the USB-type devices connected to the system.
This article shows how to develop a simple file system Mini-filter driver. However, it may also interest people without Windows driver development experience. The article requires essential Windows driver development and C/C++ knowledge.
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