polling sysfs and kernel module - linux-kernel

Question

I have read many posts about this same topic, but I am unable to find out what is exactly wrong with my sysfs implementation in my kernel module. I am trying to make a userspace program block on a poll untill the value changes in a sysfs file. Most people seem to not get blocking, I seem to not be able to get out of my blocking. Here is the relevent code:
kernel module:
static int sysfs_test = 88;
static ssize_t test_interrupts_show(struct device* dev, struct device_attribute* attr, const char* buf)
{
return scnprintf(buf, PAGE_SIZE, "%d\n", sysfs_test);
}
static ssize_t test_interrupts_store(struct device* dev, struct device_attribute* attr, const char* buf, size_t count)
{
kstrtol(buf, 10, &sysfs_test);
return count;
}
static DEVICE_ATTR(interrupts, S_IWUSR | S_IRUGO, test_interrupts_show, test_interrupts_store);
static int __init test_init(void)
{
int result;
if(dev_major)
{
dev = MKDEV(dev_major, dev_minor);
result = register_chrdev_region(dev, NUM_DEVICES, name);
} else {
result = alloc_chrdev_region(&dev, dev_minor, NUM_DEVICES, name);
dev_major = MAJOR(dev);
dev_minor = MINOR(dev);
}
if(result < 0) {
printk(KERN_WARNING "%s: can't get major %d\n", name, dev_major);
return -1;
}
printk(KERN_NOTICE "%s: Major = %d, Minor = %d\n", name, dev_major, dev_minor);
// Register as character device
test_cdev = cdev_alloc();
cdev_init(cajun_cdev, &test_fops); // Initialize cdev structure
test_cdev->owner = THIS_MODULE; // Add owner
result = cdev_add(test_cdev, dev,1); // Tell kernel about our device
if(result)
{
printk(KERN_NOTICE "Error %d adding cdev\n", result);
goto OUT2;
}
// This stuff relates to sysfs:
ctest_class = class_create(THIS_MODULE, NAME);
if(IS_ERR(test_class))
{
printk(KERN_ALERT "Failed to register device class\n");
goto OUT2;
}
test_device = device_create(test_class, NULL, dev, NULL, NAME);
if(IS_ERR(test_device))
{
printk(KERN_ALERT "Failed to create device\n");
goto OUT3;
}
result = device_create_file(test_device, &dev_attr_interrupts);
if (result < 0)
{
printk(KERN_ALERT "failed\n");
}
OUT3:
class_unregister(test_class);
class_destroy(test_class);
OUT2:
cdev_del(test_cdev);
OUT1:
unregister_chrdev_region(dev, NUM_DEVICES);
return -1;
}
Relevent userspace code:
char interrupts_path[] = "/sys/class/test_module/test_module/interrupts";
int main()
{
struct pollfd fds;
fds.fd = open(interrupts_path, O_RDWR | O_SYNC);
char dummy_buff[1];
read(fds.fd, dummy_buff, 1);
lseek(fds.fd, 0, SEEK_SET);
fds.events = POLLPRI;
printf("Polling for interrupt\n");
poll(&fds,1,-1);
printf("Interrupt occured\n");
return 0;
}
I run my userspace code in the background (./test &) and then I echo a new value into the sysfs file for interrupts. I am hopping for my userspace program to unblock and return when the value changes. What am I doing wrong here?
edit:
struct file_operations test_fops = {
.owner = THIS_MODULE,
.llseek = test_llseek,
.read = test_read,
.write = test_write,
.unlocked_ioctl = test_ioctl,
.open = test_open,
.release = test_release
};