CODEWITHSUNDEEP
kerneltime.h
Jemo
Jemo

Reputation: 309

Linux kernel add_timer

I am writing a module for kernel. I need to wait a process for a while (for example; 20 seconds) just test something. Process should go on after 20 seconds. In my module_init function I used timer like that :

init_timer(&timer);
timer.expires = jiffies + HZ*20;//timer expires in delay ticks
timer.data = 0;//zero is passed to the timer handler
timer.function = timer_handle;//function to run when timer expires

"timer" is a struct that defined like that 

static struct timer_list timer;

timer_handle is my function to run when timer expires:

void timer_handle (unsigned long data){


 }

Now in my function :

ssize_t write(struct file *filp, const char *buff, size_t count, loff_t *offp) { 
    unsigned long ret;


    printk(KERN_INFO "pid : .%d  \n", task->pid);
    down_write(&rwsem);
    if ( (filp->f_flags & O_ACCMODE) == O_RDONLY)
    {
        printk(KERN_INFO "The reader thread is not able to write. \n");
        return -EINVAL;
    }
    printk(KERN_INFO "Inside write 1 \n");
    add_timer(&timer);
    ret = copy_from_user(bufferr, buff, count);
    up_write(&rwsem);
    printk("Inside write 2 \n");
    return count;
}

After "printk(KERN_INFO "Inside write \n");" I want to keep process 20 seconds in waiting. The message "Inside write 2 \n" must written after 20 second the message "Inside write 1 \n" written. I used add_timer(&timer); between them but it does not work. I enter "dmesg" in terminal and the messages are written consecutively immediately.

I hope I explained my problem clearly :) Could anyone help me?

Upvotes: 1

Views: 2239

Answers (2)

John
John

Reputation: 449

you are printing it wrong, as since its a write callback when user triggered a read.

when do you want to register the timer? I couldn't get it why you do in the write.

is that timer should timer periodically or on basis of some event trigger?

Upvotes: 1

Federico
Federico

Reputation: 3892

Two messages are written consecutively immediately beacuse they are consecutively immediately. You are programming a timer not a delay, so after 20 seconds kernel run the timer_handle() function, which is empty in your case.

If you need to delay some code execution read Linux Device Driver 3th Chapter 7 section 3

Upvotes: 2

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