Simple custom linux kernel drivers

####kthreads.c: single suicidal kernel thread

1. Compile the task initialization and cleanup into a module. This will produce a .ko file.

   $ cd drivers/kthreads && make

2. Insert the module into the kernel

   $ sudo insmod kthreads.ko

3. Check that the task is running and watch the task lifecycle

   $ ps -ef | grep erin_thread $ tail -f /var/log/{messages,kernel,dmesg,syslog}

####erin.c: static msg producer and sink character device

1. Compile the driver into a module, which can be loaded as a character device. This will produce a .ko file.

   $ cd drivers/character_devices/simple && make

2. Make a new device node

   $ sudo mknod /dev/erin c 250 0
$ sudo chmod a+r+w /dev/erin

3. Insert a module into the linux kernel

   $ sudo insmod erin.ko

4. Check that the module is loaded

   $ cat /proc/modules | grep erin

5. Check that the module is listed as a character device

   $ cat /proc/devices | grep erin

6. Watch what the device is doing

   $ tail -f /var/log/{messages,kernel,dmesg,syslog}

7. Try using it

   $ cat /dev/erin
$ echo "hi" > /dev/erin

####block.c: a block device backed by simple kernel buffer

1. Compile

   $ cd drivers/block_devices/simple && make

2. Insert the module into the kernel

   $ sudo insmod block.ko

3. Add a new partition the disk

   $ fdisk /dev/sbd0
> n (new partition)
> p (primary partition)
> 1 (first partition number)
> (use defaults)
> w (write changes)

4. Make a filesystem at the first partition

   $ mkfs /dev/sbd0p1

5. Mount the filesystem

   $ mount /dev/sdb0p1 /mnt

6. Create a file in the filesystem, and read from it, and check the size.

   $ echo "Hi erin" > /mnt/file1
$ cat /mnt/file1
$ ls /mnt

7. Cleanup

   $ unmount /mnt

... If something goes wrong, and your kernel doesn't have CONFIG_MODULE_FORCE_UNLOAD set, you have no choice but to reboot.