Driver Descriptions

Drivers are CFM code fragments and must export driver description structures to characterize their functionality and origin. The structures must be exported through the CFM's symbol mechanism, using the symbol name TheDriverDescription. The complete structure is defined in Driver Loader Library. It is based on the driver-descriptor property associated with device entries in the Name Registry, described in Name Registry.

Note

Open Firmware uses the driver-descriptor property and the Mac OS uses TheDriverDescription symbol to refer to the same structure.

The DriverDescription structure is used by scanning code to

match Registry entries to drivers
identify device entries by service type or family
provide driver version information
provide driver initialization information
allow replacement of ROM-based drivers with newer disk-based drivers

By providing a common structure to describe drivers, the system is able to regularize the mechanisms used to locate, load, initialize, and replace them. Details of how this works are given in Finding, Initializing, and Replacing Drivers.

Mac OS treats any CFM code fragment that exports a driver description structure as a native driver.