Kernel thread to print the running tasks on the CPU every 500ms

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What is  Kernel Thread?

 A Kernel Thread is a Linux Task running only in kernel mode. It is not created by running fork() or clone() system calls.

What is the use of Kernel Thread?

 Kernel Threads helps the kernel to perform operations in background.

What are the some examples of Kernel Thread?

 1. ksoftirqd is Per CPU kernel thread runs processing softirqd.
2. kworker is a kernel thread which processes work queues.

What are the differences between Kernel Thread and User Thread?

 Both Kernel Thread and User Thread are represented by task_struct. The main difference is that there is no address space in kernel threads. mm variable of task_struct is set to NULL.

How to Create a Kernel Thread?

 API For creating a kernel thread.

#include <linux/kthread.h>
struct task_struct *kthread_create(int (*threadfn)(void *data), void *data, const char name[], ...)

Parameters:

threadfn -> the function which thread should run
data -> Argument for thread function
name -> Printf style format for the name of kernel thread.

Return Value: Pointer to struct  task_struct

kthread_create only creates the thread but doesn't run the thread, we need to call wake_up_process() with the return value of kthread_create as an argument to the wake_up_process for the thread function to run.

Linux provides an API which creates the kernel thread and calls wake_up_process().

struct task_struct * kthread_run(int (*threadfn)(void *data), void *data, const char name[], ...)

To stop the kernel thread.

int kthread_stop(struct task_struct *k);

If you don't stop the kernel thread in your module_exit function, you will get oops message.

kthread_stop is a blocking call, it waits until the function executed by thread exits. kthread_stop() flag sets a variable in the task_struct variable which the function running in while(1) should check in each of its loop.

while(1)
{
     while(!kthread_should_stop())
     {
                //perform operations here
      }
}




Code:



Output:




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