A controller object represents a hardware adapter or controller with homogenous devices that are the actual targets for I/O requests. A controller object can be used to synchronize a device driver's I/O to the target devices through its hardware adapter/controller.
A controller object is partially opaque. Driver writers must know about a certain field associated with the controller object because their drivers access this field through the controller object pointer returned by IoCreateController. The following field in a controller object is accessible to the creating driver.
Accessible Fields
PVOID ControllerExtension
Points to the controller extension. The structure and contents of the controller extension are driver-defined. The size is driver-determined, specified in the driver's call to IoCreateController. Usually, drivers maintain common state about I/O operations in the controller extension and device-specific state about I/O for a target device in the corresponding device extension.
Comments
Most driver routines that process IRPs are given a pointer to the target device object. Consequently, device drivers that use controller objects frequently store the controller object pointer returned by IoCreateController in each device extension.
Note that a controller object has no name so it cannot be the target of an I/O request, and higher-level drivers cannot connnect or attach their device objects to a device driver's controller object.
Undocumented fields within a controller object should be considered inaccessible. Drivers with dependencies on object field locations or access to undocumented fields might not remain portable and interoperable with other drivers over time.
See Also