A printer driver in BeOS R5 is an add-on that exports a specific C interface. This add-on is used by the print_server to add a new printer, configure a page, configure the print job, and print the print job on the printer. This article describes how the print_server interfaces with the printer driver.
The print_server is responsible for maintaining common settings. BMessage objects are used to pass settings from the print_server to a printer driver and vice versa. If the printer driver has to return a BMessage object and wants to show the successful completion of an operation, it has to set the field what to the value 'okok'. To indicate an error, the preferred method is to return NULL. In some cases the print_server interprets a value in what other than 'okok' as the failure of an operation. A printer driver should not rely on this; instead, it should return NULL.
