Question

• Design a kernel module that creates a /proc file named /proc/jiffies that reports the current value of jiffies when the /proc/jiffies file is read, such as with the command

  cat /proc/jiffies
  Be sure to remove /proc/jiffies when the module is removed.

Please help with this assignment using C programming and testing in Linux Ubuntu.

Answer 1

#As per the question first, we have to include the head file that is <linux/jiffies.h> as we are using the jiffies from this head file.

/proc:- It is file system that only exist in the kernel memory and used for the pre-process stats.

int proc_init(void)

{
/* creates the /proc/jiffies entry */
        proc_create(PROC_NAME, 0666, NULL, &proc_ops);
        return 0;
}

void proc_exit(void)
{
        /* removes the /proc/jiffies entry */
        remove_proc_entry(PROC_NAME, NULL);
}

In this /proc/jiffies file is removed in the module exit point proc_exit()using the function remove_proc_entry().

size_t proc_read(struct file *file, char __user *usr_buf, size_t count, loff_t *pos)
{
        int rv = 0;
        char buffer[BUFFER_SIZE];
        static int completed = 0;
        
        if (completed) {
                completed = 0;
                return 0;
        }
        
        completed = 1;
        
        rv = sprintf(buffer, "%lu\n", jiffies);
        
        /* copies kernel space buffer to user space usr buf */
        copy_to_user(usr_buf, buffer, rv);
        
        return rv;
}

#In the above code we use the unassigned long in into the variable buffer which exists in the kerenel memory. As /proc/jiffies can be accesed from the user space

#Now we have to make a file and enter this

#Make file

obj-m += jiffies.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

#Output would be like this :