IRP Major Function Codes
Each driver-specific I/O stack location (IO_STACK_LOCATION) for every IRP contains a major function code (IRP_MJ_XXX), which tells the driver what operation it or the underlying device driver should carry out to satisfy the I/O request. Each kernel-mode driver must provide dispatch routines for the major function codes that it must support.
The specific operations a driver carries out for a given IRP_MJ_XXX code depend somewhat on the underlying device, particularly for IRP_MJ_DEVICE_CONTROL and IRP_MJ_INTERNAL_DEVICE_CONTROL requests. For example, the requests sent to a keyboard driver are necessarily somewhat different from those sent to a disk driver. However, the I/O manager defines the parameters and I/O stack location contents for each system-defined major function code.
Every higher-level driver must set up the appropriate I/O stack location in IRPs for the next-lower-level driver and call IoCallDriver, either with each input IRP, or with a driver-created IRP (if the higher-level driver holds on to the input IRP). Consequently, every intermediate driver must supply a dispatch routine for each major function code that the underlying device driver handles. Otherwise, a new intermediate driver will "break the chain" whenever an application or still higher-level driver attempts to send an I/O request down to the underlying device driver.
File system drivers and legacy file system filter drivers also handle a required subset of system-defined IRP_MJ_XXX function codes, some with subordinate IRP_MN_XXX function codes. For more information on how to handle these IRPs, see IRP major function codes for file system drivers and legacy FS filter drivers.
Drivers handle IRPs set with some or all of the following major function codes:
IRP_MJ_INTERNAL_DEVICE_CONTROL
The input and output parameters described in this section are the function-specific parameters in the IRP.
For more information about IRPs, see Handling IRPs.