How to add a new Linux Kernel Module (LKM)

To demonstrate, let us goto a simple “Hello World” as a module and inserted in to the kernel

Step 1
Open any editor like vi or gedit in a shell prompt and the type the following
/* Name of the file is hello.c */
#include <linux/module.h>
#include <linux/kernel.h>
int init_module(void)
{
printk(KERN_INFO “Hello world.n”);
return 0;
}
void cleanup_module(void)
{
printk(KERN_INFO “Goodbye worldn”);
}


The above is a simple C program that displays “Hello world” when the module is inserted and displays “Goodbye world” when the module is removed.
Step 2
The program can be compiled using gcc compiler in the shell prompt itself, but we need to write the commands twice or more. So to compile shortly let us write a makefile to compile the above program
The make file should be named as Makefile (See the First letter M is uppercase and there should not be any space between Make and file)
Copy and paste the following lines in an editor (vi or gedit)
obj-m += hello.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
Step 3
after this, execute the following command
# make
You will get the following output which indicates there is no error
make -C /lib/modules/2.6.27.5-117.fc10.i686/build M=/home/pradeepkumar/lsp modules
make[1]: Entering directory `/usr/src/kernels/2.6.27.5-117.fc10.i686′
Building modules, stage 2.
MODPOST 1 modules
make[1]: Leaving directory `/usr/src/kernels/2.6.27.5-117.fc10.i686′
The make command creates new set of files like hello.ko, hello.mod.o, modules.order, etc
Step 4
The .ko indicates it is a kernel object, but ordinary C compiler generates only an object file..
go to the shell prompt (open the terminal) execute the command one by one
# su
The above command waits for the root password, please provide the password
# insmod
inserting the module
# lsmod
listing all the modules running under the kernel, you can see the first module will be listed as hello
# dmesg
you can see thelast line says hello world
# rmmod
removing the module
# dmesg
you can see the last line says goodbye world
Like this we can write many modules and can be inserted to the kernel..

Comments

  1. bhasker bhashwaram28 January 2010 at 16:47

    thanks for the simple steps for inserting a module. i could do it. sir i am recently doing a course in TIFAC on wireless and embedded system 16bit. please suggest one project in this field so that learning would become more easy and interesting

    bhasker bhashwaram
    07bce079
    b batch
    cse

    ReplyDelete
  2. Sir,
    this is not working in fedora 12.
    Even kernel compilation didnt work successfuly on fedora 12
    kindly help on this

    kumar akshay
    07bce165
    c batch

    ReplyDelete

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