Basically, a kernel module it's one piece of code that can be loaded and unloaded into the kernel.
You can read about kernel modules from here.
Now, let's try to make a simple kernel module.
Writing your own module can be done if you know some basic rules.
First, about how to use modules.
Suppose you have a new module named kernelmoduletest.
How to load the module.
Just use this command in your module kernel folder:
#insmod kernelmoduletest.ko This can be done with:
#dmesg | tail $ rmmod kernelmoduletest
ERROR: Removing 'kernelmoduletest': Operation not permitted Then use the rmmod command.
Know how to make the kernel module skeleton.
This is not very simple because you need to know many things about kernel and programming.
But you can try the test with some simple example like this example:
Create the c file named kernelmoduletest and add this source code:
#include <linux module.h="">
#include <linux kernel.h="">
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("kernelmoduletest");
MODULE_AUTHOR("Catalin George Festila/mythcat/catafest");
int init_module() {
printk(KERN_INFO "Now I will initialize my kernel module\n");
printk(KERN_INFO "Test: Hello World !\n");
return 0;
}
void cleanup_module() {
printk(KERN_INFO "Bad!... kernel module unloaded.\n");
}</linux></linux> Add this to tell how to compile the kernel module.
obj-m += kernelmoduletest.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean Just use make command.
# make
...
Building modules, stage 2.
MODPOST 1 modules
...
make[1]: Leaving directory `/usr/src/linux-headers-2.6.31-14-generic'
[14694.779227] Now I will initialize my kernel module
[14694.779233] Test: Hello World !
[15049.825605] Bad!... kernel module unloaded. Thank you. Regards.
