jiffies

jiffies

Jiffies is a global variable defined in Linux header linux/jiffies.h, it represents the number of ticks of system clock from system boot till the time it's value is read. We'll display it's value in a proc file

Pre-requisites

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

Steps

Almost similar to hello module, just we output current value of jiffies.

• Navigate to Project directory

cd jiffies

• compile Module

sudo make

• Look for jiffies in loaded Modules

sudo lsmod | grep jiffies

You will get no results

• Look for file jiffies in proc fs

cat /proc/jiffies

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

• Insert Module

sudo insmod jiffies.ko

• Again check for jiffies in module list

sudo lsmod | grep jiffies

Now you will see the jiffies module listed

• Check the proc file again

cat /proc/jiffies

Now we can see Current Jiffies value = 4299321332 !

• Remove the Module and verify it's gone

sudo rmmod jiffies
sudo lsmod | grep jiffies

No output means module is removed

• Check for proc file again

cat /proc/jiffies

Understanding the Code

• Additional Header(s)

#include <linux/jiffies.h>

• Inside proc_read modified sprintf

rv = sprintf(buffer,"Current Jiffies value = %lu\n" ,jiffies);

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 : seconds Module