6.1.1 Commonly Implemented Dispatch Routines

In general, most NT drivers must handle some or all of the following requests:

• IRP_MJ_CREATE indicates either that a user-mode protected subsystem, possibly on behalf of an application or subsystem-specific driver, has requested a handle for the file object associated with the target device object, or that a higher-level NT driver is connecting or attaching its device object to the target device object.

• IRP_MJ_CLEANUP indicates that the handle for the file object, representing the target device object, is being closed, so any IRPs currently queued to the target device for the given file object, found in the driver’s I/O stack location of the cleanup IRP, should be cancelled.

• IRP_MJ_CLOSE indicates that the handle of the file object that represents the target device object or a pointer to the target device object has been closed and that there are no outstanding references to the file object pointer.

• IRP_MJ_READ indicates an I/O request to transfer data from the underlying physical device to the system.

• IRP_MJ_WRITE indicates an I/O request to transfer data from the system to the underlying physical device.

• IRP_MJ_DEVICE_CONTROL indicates a request with a system-defined, device-type-specific I/O control code specifying a particular device operation is being sent to a device driver.

  For more information about the system-defined (sometimes called public) I/O control codes that NT device drivers must support, see the Kernel-mode Driver Reference. Note that higher-level NT drivers also must support IRP_MJ_DEVICE_CONTROL to pass these IRPs on to their underlying device drivers.

• IRP_MJ_INTERNAL_DEVICE_CONTROL indicates a request sent to the device driver, in most cases from a closely coupled higher-level driver, usually with a privately defined, driver-specific and device-type-specific or device-specific I/O control code requesting a device-type-specific or device-specific operation.

  Only certain kinds of NT drivers are required to handle system-defined internal device I/O control requests, including certain SCSI drivers, keyboard or mouse device drivers, and parallel drivers that interoperate with system-supplied drivers.

The Dispatch routine entry points that any NT driver must set in its driver object vary according to the type and functionality of the underlying physical device. For device-type-specific information about IRP major function codes that NT device drivers must handle, see the Kernel-Mode Driver Reference. For information about SCSI and video miniport drivers, see Appendix A and the Kernel-Mode Graphics Driver Guide, respectively. For more information about other types of SCSI drivers, see also Appendix A.