Linux driver polling?

Question

I'm starting to learn Linux driver development. I am trying to create a simple driver that polls a function which in the end will read a hardware register at a constant rate (i.e. 10 times a second) and adds the hardware output to a queue which can then be accessed by procfs.

First things first. I need to be able to poll at a consistent rate. I have been reading this online a lot and it seems very simple (my code below). However, when I insmod my module, it doesn't seem to poll at all!!

Can someone please help me understand this and help me figure out what I need to do to make it poll?

I really appreciate you guys' help!

#include <linux/init.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/version.h>

#include <linux/sched.h>
#include <linux/kernel.h> /* printk() */
#include <linux/fs.h>     /* everything... */
#include <linux/errno.h>  /* error codes */
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/ioport.h>
#include <linux/poll.h>


MODULE_LICENSE("Dual BSD/GPL");


int silly_open(struct inode *inode, struct file *filp)
{
        printk(KERN_ALERT "open\n");
        return 0;
}

int silly_release(struct inode *inode, struct file *filp)
{
        printk(KERN_ALERT "release\n");
        return 0;
}

ssize_t silly_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
        printk(KERN_ALERT "read\n");
        return 0;
}

ssize_t silly_write(struct file *filp, const char __user *buf, size_t count,
                    loff_t *f_pos)
{
        printk(KERN_ALERT "write\n");
        return 0;
}

unsigned int silly_poll(struct file *filp, poll_table *wait)
{
        printk(KERN_ALERT "poll\n");
    return POLLIN | POLLRDNORM | POLLOUT | POLLWRNORM;
}


struct file_operations silly_fops = {
        .read =     silly_read,
        .write =    silly_write,
        .poll =     silly_poll,
        .open =     silly_open,
        .release =  silly_release,
        .owner =    THIS_MODULE
};

int silly_init(void)
{       printk(KERN_ALERT "init\n");
        return 0;
}

static int hello_init(void)
{
        printk(KERN_ALERT "Hello, world\n");
        return 0;
}

static void hello_exit(void)
{
        printk(KERN_ALERT "Goodbye, cruel world\n");
}

module_init(hello_init);
module_exit(hello_exit);

score 0 · Answer 1 · answered Oct 07 '15 at 14:24

In hello_init(), you don't connect silly_fops to it. It cannot work automatically if there is no any connection between them.

In order to connect, you probably need to initialize a device with silly_fops(), refer to ch3.4 of ldd3 at http://www.makelinux.net/ldd3/, hope this works.

Linux driver polling?

1 Answers1