seconds

Lifespan of a module

Dynamically calculate the time duration passed since a module is loaded, and display the value in seconds again in proc file named seconds. Along with jiffies, we'll utilize another constant variable named HZ, which represents the tick frequency, to calculate time elapsed since module was loaded.

Pre-requisites

• Finish workspace setup
• Understand workflow
• Download the folder seconds to local workspace

Steps

Almost similar to hello & jiffies, just we calculate and output time elapsed since module loaded.

• Navigate to Project directory

cd seconds

• compile Module

sudo make

• Look for seconds in loaded Modules

sudo lsmod | grep seconds

You will get no results

• Look for file seconds in proc fs

cat /proc/seconds

you will see : cat: proc/seconds: No such file or directory

• Insert Module

sudo insmod seconds.ko

• Again check for seconds in module list

sudo lsmod | grep seconds

Now you will see the seconds module listed

• Check the proc file again

cat /proc/seconds

Now we can see Module living for 14 seconds !
each time we read seconds proc file, we will see a new value, which is dynamically calculated when read!

• Remove the Module and verify it's gone

sudo rmmod seconds
sudo lsmod | grep seconds

No output means module is removed

• Check for proc file again

cat /proc/seconds

Understanding the Code

• Additional Header(s)

#include <asm/param.h>

• Initialize a variable to store jiffies at module load

static unsigned long jiffies_init;

• Store jiffies into jiffies_init at module load inside proc_init

jiffies_init = jiffies;

• Inside proc_read modified sprintf

rv = sprintf(buffer,"Module living for %lu seconds\n" ,(jiffies-jiffies_init)/HZ);

We calculate effective duration since module was loaded using current jiffies and jiffies_init, together with HZ contant.

Note : We declare custom functions and variable as static, this is to limit their scope to current module,otherwise they would be accessible in whole of Kernel and pollute global namespace!

Next up : What's next