The pseudo device driver presented in this section writes a constant string to a system log when the driver is loaded.
This first version of the Quote Of The Day driver (qotd_1) is even more simple than the dummy driver from the previous chapter. The dummy driver includes all functions that are required to drive hardware. This qotd_1 driver includes only the bare minimum functions it needs to make a string available to a user command. For example, this qotd_1 driver has no cb_ops(9S) structure. Therefore, this driver defines no open(9E), close(9E), read(9E), or write(9E) function. If you examine the dev_ops(9S) structure for this qotd_1 driver, you see that no getinfo(9E), attach(9E), or detach(9E) function is defined. This driver contains no function declarations because all the functions that are defined in this driver are declared in the modctl.h header file. You must include the modctl.h header file in your qotd_1.c file.
This qotd_1 driver defines a global variable to hold its text data. The _init(9E) entry point for this driver uses the cmn_err(9F) function to write the string to a system log. The dummy driver also uses the cmn_err(9F) function to display messages. The qotd_1 driver is different from the dummy driver because the qotd_1 driver stores its string in kernel memory.