Kernel Module Code :

How to run :

    1. ~$ cd mp1/
    2. ~$ make
    3. ~$ sudo insmod mp1.ko

To check for process times :

    ~$ cat /proc/mp1/status

To remove the module

    ~$ sudo rmmod mp1

Kernel Description

Initialization:

    1.  Initialize the kernel linked list  *test_head* used to maintain the file data
    2.  I created the **mp1** directory and **status** file for processess to register
    3.  Initialize the workqueue *my_wq* to handle bottom halve of interrupt handler
    4.  Setup a timer and the associated intterupt handler, and set the timer to a given interval

Callbacks:

    Callbacks are used to define the read and write to the */proc/mp1/status* file.

mp1_read:

        To handle the read from the file, when the request comes, we verify correct parameters. Following this we acquire a lock and read all contents of the linked list to a buffer. Finally we write the buffer to userspace, allowing procs to read the data stored.

mp1_write:

        This function handles the write request (registration) of a new process to the file system. 
        I read the pid supplied from the user, and convert the pid to int using *kstrtoint_from_user* function. Following this I check if the pid values are correct and the we append it to the linked list : *test_head*, initializing the cpu_time as 0.

Timer Interrupt

        I initialized the timer using *setup_timer* and attached it to the interrupt handler function : *my_timer_callback*. And then modified the timer to run after 5 second.
        Inside the interrupt handler, **my_timer_callback** : *setup_work* function, initializes a work of updating the list and adds it to the workqueue. And then modify the timer for another 5 second.

Updating the Linked List (The queued work)

        The queued work, calls the **upDateFunction**, which iterates over the linked list *test_head*, and either updates or deletes the entry based on the output of the **get_cpu_use**, function. The updation is done under a spin lock, to prevent any inconsistency in the list, if other functions are called.

UserApp:

I created an application , which register to proc and calculate fibonnaci for 1000 times

Compiling and Running

    ~$gcc -o userapp userapp.c
    ~$./userapp <Fib Number>

Registration:

    This code , registers to */proc/mp1/status*, using system call for 'echo PID > /proc/mp1/status'