Operting system question, please write code in C. I will give good ratings for a

Question

Operting system question, please write code in C. I will give good ratings for answers with explanations.

It is time to move from programming with system calls to actually creating kernel code. In this project you will create a kernel module for linux version you had setup as per the instructions online. Your module will be defined in a file named 142-km.c and do the following:

1.-When your kernel module is loaded it will print out to /var/log/messages the following message (verbatim):

"142-km loaded!"

2.-When the kernel module is removed it will print the following message (verbatim) in the same log file as above:

"142-km removed!"

3.-While loaded, your module will add the file 142-km to the "proc" file system and act as an 'echo' file, anything written should be read back as it was written. I.e. if I do echo "This is a km test" > /proc/142-km and then do cat /proc/142-km, you should see the following text in the screen: "This is a km test". Further read from the file should find the file empty.

Explanation / Answer

Answer for Q1 and Q2 : Code for kernel module

/*
* 142-km.c - The simplest kernel module.
*/
#include <linux/module.h>   /* Needed by all modules */
#include <linux/kernel.h>   /* Needed for KERN_INFO */

int init_module(void)
{

   /*loads this message in the /var/log/messages when the kernel is loaded*/
   printk(KERN_INFO "142-km loaded! ");

   /*
   * A non 0 return means init_module failed; module can't be loaded.
   */
   return 0;
}

void cleanup_module(void)
{

   /*loads this message in the /var/log/messages when the kernel is cleaned or deleted.
   printk(KERN_INFO "142-km removed! ");
}

Kernel modules must have at least two functions:

a) A "start" (initialization) function called init_module() which is called when the module is insmoded into the kernel
b) An "end" (cleanup) function called cleanup_module() which is called just before it is rmmoded.

Every kernel module needs to include linux/module.h which is only used for the macro expansion for the printk() log level, KERN_ALERT

Compiling the kernel module :

obj-m += 142-km.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

Now you can compile the module by issuing the command "make".
command : make

Kernel modules now have a .ko extension (in place of the old .o extension) which easily distinguishes them from conventional object files. Now to insert your freshly compiled module it into the kernel with insmod ./142-km.ko. All modules loaded into the kernel are listed in /proc/modules. Go ahead and cat that file to see that your module is really a part of the kernel.To remove your module from the kernel by using "rmmod 142-km".

Now take a look at /var/log/messages just to see that it got logged to your system logfile.

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