Storage Filter Driver's Support of I/O Requests

A higher-level storage filter driver (SFD) intercepts IRPs from user applications and higher-level drivers and modifies them as needed before passing them to the next-lower driver (a storage class driver or another filter driver). Such an SFD supplies device-specific support for requests that require special handling, such as translating data sent to or returned from the device in a nonstandard format, or programming the device in response to an IRP_MJ_DEVICE_CONTROL request.

A lower-level SFD monitors SRBs and/or IRPs issued by a storage class driver and modifies them as needed before passing them to the next-lower driver (a storage port driver or another filter driver).

Both higher- and lower-level SFDs can let the lower drivers process all I/O requests that require no special handling.

Like a storage class driver, an SFD has the following requirements common to all higher-level kernel-mode drivers:

• It must supply a set of Dispatch routines to which the I/O manager and/or still higher-level drivers can send IRPs for appropriate I/O operations. An SFD must support the same set of IRP_MJ_XXX as the storage class driver for its type of device.

• For IRP_MJ_DEVICE_CONTROL requests, it must support as many of the class driver-supported I/O control codes as its physical device can handle and, if possible, emulate support for any remaining I/O control codes in the driver.

• It must have a DriverEntry routine, an AddDevice routine, an Unload routine, and Dispatch routines to handle PnP and power IRPs and can have any other standard higher-level driver routine, such as IoCompletion routines, as necessary.

• It must follow the rules for processing PnP, power management, and system control IRPs.

If its device has special features, an SFD can support a set of driver-defined I/O control codes in addition to the system-required set of device-type-specific I/O control codes for IRP_MJ_DEVICE_CONTROL requests.