A simple charactor device driver code using sysfs and udev

 

/* test.c
 * use "insmod test.ko"
 * can see "/dev/test"
 * and "test" in "/proc/devices"
 */


#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/types.h>    /* dev_t */
#include <linux/cdev.h>        /* struct cdev */
#include <linux/device.h>    /* device_create() */
#include <linux/fs.h>        /* struct file_operations */


#define DEVICE_NAME "test"

static struct cdev test_dev;
static struct class *test_class;
static dev_t test_devno;

static int test_open(struct inode *inode, struct file *filp)
{
    printk(KERN_ALERT "The process is \"%s\" (pid %i)\n",
        current->comm, current->pid);
    return 0;
}


static struct file_operations test_fops = 
{
    .owner = THIS_MODULE,
    .open = test_open,
};

static int __init test_init(void)
{
    int ret;
    unsigned int first_minor = 0;
    unsigned int count = 1;
    /* get dev_t from kernel */
    ret = alloc_chrdev_region(&test_devno,first_minor,count,DEVICE_NAME);
    if(ret < 0) return ret;

    /* init cdev and fops */
    cdev_init(&test_dev,&test_fops);
    test_dev.owner = THIS_MODULE;/* add the dev_t to cdev */
    cdev_add(&test_dev, test_devno,count);

    /* create a class named as DEVICE_NAME, show as /sys/class/DEVICE_NAME */
    test_class = class_create(THIS_MODULE, DEVICE_NAME);
    if(IS_ERR(test_class))
    {
        printk(KERN_ALERT "create test_class error.");
        return -1;
    }

    /* create device by /sys/class/DEVICE_NAME and the dev_t, show as /dev/DEVICE_NAME */
    device_create(test_class,NULL,test_devno,NULL,DEVICE_NAME);
    printk(KERN_ALERT DEVICE_NAME " initialized\n");
    return 0;
}

static void __exit test_exit(void)
{
    unsigned int count = 1;
    cdev_del(&test_dev);
    unregister_chrdev_region(test_devno,count);
    device_destroy(test_class,test_devno);
    class_destroy(test_class);
    printk(KERN_ALERT DEVICE_NAME " released\n");
}

module_init(test_init);
module_exit(test_exit);

MODULE_LICENSE("GPL");

 

#Makefile

OBJ=test

ifneq ($(KERNELRELEASE),)
    obj-m := ${OBJ}.o
    module-objs := ${OBJ}.o

else

    KERNELDIR := /lib/modules/$(shell uname -r)/build
    PWD := $(shell pwd)
defualt:
    $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

endif


clean:
    rm *.o *.ko *.mod.c