motd.ko

Just a simple exercise to practice the concepts detailed in Linux Device Drivers 3rd edition (Chapter 3: Char Devices) before I moved on to reproducing the 'scull' device driver described in the textbook.

Building

The Makefile should be sufficient for an out-of-tree build:

$ make

Running

Load the module by running motd_load.sh. This will create a device special file named /dev/motd0.

You should be able to do most things that involve reading and writing to the device.

I committed a text file that can be used for some quick tests in this repo.

$ cp test-motd.txt /dev/motd0
$ cat /dev/motd0
=======================
  Message of the Day
=======================

Hello, potato!

Opening /dev/motd0 in write only mode should truncate the contents of the MOTD just like any other file.

Remarks

The size of your MOTD is limited only by the amount of memory installed on your system :-) -- I haven't added any limits to the driver.

Getting rid of motd.ko :'-(

Close any file descriptors you have open to the device and then run the motd_unload.sh script from this repository. This will unload the driver and remove the special file.