class 에 sysfs node 등록하여 사용하기

linux kernel 에서 kernel 단과 user 사이에 통신을 위한 방법중에 sysfs node 를 사용하는 방법이 있다.

지원하는 함수는 아래 3가지 함수들이 있다.

devclass_create_file

device_create_file

class_create_file

이중 devclass_create_file 은 삭제된 것으로 보인다.
class_create_file 의 예제를 첨부한다.


null_driver.c

Makefile

#include <linux/module.h>
#include <linux/version.h>
#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/kdev_t.h>
#include <linux/fs.h>
#include <linux/device.h>
#include <linux/cdev.h>
 
static dev_t first; // Global variable for the first device number 
static struct cdev c_dev; // Global variable for the character device structure
static struct class *cl; // Global variable for the device class
static int my_open(struct inode *i, struct file *f)
{
  printk(KERN_INFO "Driver: open()\n");
  return 0;
}
  static int my_close(struct inode *i, struct file *f)
{
  printk(KERN_INFO "Driver: close()\n");
  return 0;
}
  static ssize_t my_read(struct file *f, char __user *buf, size_t
  len, loff_t *off)
{
  printk(KERN_INFO "Driver: read()\n");
  return 0;
}
  static ssize_t my_write(struct file *f, const char __user *buf,
  size_t len, loff_t *off)
{
  printk(KERN_INFO "Driver: write()\n");
  return len;
}
  static struct file_operations pugs_fops =
{
  .owner = THIS_MODULE,
  .open = my_open,
  .release = my_close,
  .read = my_read,
  .write = my_write
};
 
int g_data = 10;
static ssize_t sysfs_show_func(struct class *cls, struct class_attribute *attr, char *buf)
{
	printk("%s() g_data=%d\n", __func__, g_data);
	return sprintf(buf, "data : %d\n" ,g_data);
}

static ssize_t sysfs_store_func(struct class *cls, struct class_attribute *attr, const char *buf, size_t count)
{
	int value;
	sscanf(buf, "%d", &value);
	printk("%s() value=%d\n", __func__, value);
	g_data = value;

	return count;
}

static CLASS_ATTR(onegun_sysfs, S_IWUSR | S_IRUGO, sysfs_show_func, sysfs_store_func);

static int __init ofcd_init(void) /* Constructor */
{
int ret = 0;
  printk(KERN_INFO "Namaskar: ofcd registered");
  if (alloc_chrdev_region(&first, 0, 1, "Shweta") < 0)
  {
    return -1;
  }
    if ((cl = class_create(THIS_MODULE, "onegun_class_driver")) == NULL)
  {
    unregister_chrdev_region(first, 1);
    return -1;
  }
    if (device_create(cl, NULL, first, NULL, "mynull") == NULL)
  {
    class_destroy(cl);
    unregister_chrdev_region(first, 1);
    return -1;
  }
    cdev_init(&c_dev, &pugs_fops);
    if (cdev_add(&c_dev, first, 1) == -1)
  {
    device_destroy(cl, first);
    class_destroy(cl);
    unregister_chrdev_region(first, 1);
    return -1;
  }

	   ret = class_create_file(cl, &class_attr_onegun_sysfs);
	if(ret)
		printk("%s() [Error] class_create_file\n", __func__);
  return 0;
}
 
static void __exit ofcd_exit(void) /* Destructor */
{
  cdev_del(&c_dev);
  device_destroy(cl, first);
  class_destroy(cl);
  unregister_chrdev_region(first, 1);
  printk(KERN_INFO "Alvida: ofcd unregistered");
}
 
module_init(ofcd_init);
module_exit(ofcd_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Anil Kumar Pugalia <email_at_sarika-pugs_dot_com>");
MODULE_DESCRIPTION("Our First Character Driver");