Every driver whose device objects belong to a particular device type (see Specifying Device Types) is required to support this request in a DispatchDeviceControl routine, if a set of system-defined I/O control codes (IOCTLs) exists for the type.
Higher-level drivers usually pass these requests on to an underlying device driver. Each device driver in a driver stack is assumed to support this request, along with a set of device type-specific, public or private IOCTLs. For more information about IOCTLs for specific device types, see device type-specific documentation in the Microsoft Windows Driver Kit (WDK).
Any time following the successful completion of a create request.
The I/O control code is contained at Parameters.DeviceIoControl.IoControlCode in the driver's I/O stack location of the IRP.
Other input parameters depend on the I/O control code's value. For more information, see Buffer Descriptions for I/O Control Codes.
Output parameters depend on the I/O control code's value. For more information, see Buffer Descriptions for I/O Control Codes.
A driver receives this I/O control code because user-mode thread has called the Microsoft Win32 DeviceIoControl function, or a higher-level kernel-mode driver has set up the request. Possibly, a user-mode driver has called DeviceIoControl, passing in a driver-defined (also called private) I/O control code, to request device- or driver-specific support from a closely coupled, kernel-mode device driver.
On receipt of a device I/O control request, a higher-level driver usually passes the IRP on to the next-lower driver. However, there are some exceptions to this practice. For example, a class driver that has stored configuration information obtained from the underlying port driver might complete certain IOCTL_XXX requests without passing the IRP down to the corresponding port driver.
On receipt of a device I/O control request, a device driver examines the I/O control code to determine how to satisfy the request. For most public I/O control codes, device drivers transfer a small amount of data to or from the buffer at Irp->AssociatedIrp.SystemBuffer.