IOCTL: usage example

ioctl is used in communication with modules of Linux.

Module:

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kdev_t.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include<linux/slab.h>                 //kmalloc()
#include<linux/uaccess.h>              //copy_to/from_user()
#include <linux/ioctl.h>
 
 
#define WR_VALUE _IOW('a','a',int32_t*)
#define RD_VALUE _IOR('a','b',int32_t*)
 
int32_t value = 0;
 
dev_t dev = 0;
static struct class *dev_class;
static struct cdev etx_cdev;
 
static int __init etx_driver_init(void);
static void __exit etx_driver_exit(void);
static int etx_open(struct inode *inode, struct file *file);
static int etx_release(struct inode *inode, struct file *file);
static ssize_t etx_read(struct file *filp, char __user *buf, size_t len,loff_t * off);
static ssize_t etx_write(struct file *filp, const char *buf, size_t len, loff_t * off);
static long etx_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
 
static struct file_operations fops =
{
        .owner          = THIS_MODULE,
        .read           = etx_read,
        .write          = etx_write,
        .open           = etx_open,
        .unlocked_ioctl = etx_ioctl,
        .release        = etx_release,
};
 
static int etx_open(struct inode *inode, struct file *file)
{
        printk(KERN_INFO "Device File Opened...!!!\n");
        return 0;
}
 
static int etx_release(struct inode *inode, struct file *file)
{
        printk(KERN_INFO "Device File Closed...!!!\n");
        return 0;
}
 
static ssize_t etx_read(struct file *filp, char __user *buf, size_t len, loff_t *off)
{
        printk(KERN_INFO "Read Function\n");
        return 0;
}
static ssize_t etx_write(struct file *filp, const char __user *buf, size_t len, loff_t *off)
{
        printk(KERN_INFO "Write function\n");
        return 0;
}
 
static long etx_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
         switch(cmd) {
                case WR_VALUE:
                        copy_from_user(&value ,(int32_t*) arg, sizeof(value));
                        printk(KERN_INFO "Value = %d\n", value);
                        break;
                case RD_VALUE:
                        copy_to_user((int32_t*) arg, &value, sizeof(value));
                        break;
        }
        return 0;
}
 
 
static int __init etx_driver_init(void)
{
        /*Allocating Major number*/
        if((alloc_chrdev_region(&dev, 0, 1, "etx_Dev")) <0){
                printk(KERN_INFO "Cannot allocate major number\n");
                return -1;
        }
        printk(KERN_INFO "Major = %d Minor = %d \n",MAJOR(dev), MINOR(dev));
 
        /*Creating cdev structure*/
        cdev_init(&etx_cdev,&fops);
        etx_cdev.owner = THIS_MODULE;
        etx_cdev.ops = &fops;
 
        /*Adding character device to the system*/
        if((cdev_add(&etx_cdev,dev,1)) < 0){
            printk(KERN_INFO "Cannot add the device to the system\n");
            goto r_class;
        }
 
        /*Creating struct class*/
        if((dev_class = class_create(THIS_MODULE,"etx_class")) == NULL){
            printk(KERN_INFO "Cannot create the struct class\n");
            goto r_class;
        }
 
        /*Creating device*/
        if((device_create(dev_class,NULL,dev,NULL,"etx_device")) == NULL){
            printk(KERN_INFO "Cannot create the Device 1\n");
            goto r_device;
        }
        printk(KERN_INFO "Device Driver Insert...Done!!!\n");
    return 0;
 
r_device:
        class_destroy(dev_class);
r_class:
        unregister_chrdev_region(dev,1);
        return -1;
}
 
void __exit etx_driver_exit(void)
{
        device_destroy(dev_class,dev);
        class_destroy(dev_class);
        cdev_del(&etx_cdev);
        unregister_chrdev_region(dev, 1);
    printk(KERN_INFO "Device Driver Remove...Done!!!\n");
}
 
module_init(etx_driver_init);
module_exit(etx_driver_exit);
 
MODULE_LICENSE("GPL");
MODULE_AUTHOR("EmbeTronicX <[email protected] or [email protected]>");
MODULE_DESCRIPTION("A simple device driver");
MODULE_VERSION("1.5");

User space

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include<sys/ioctl.h>
 
#define WR_VALUE _IOW('a','a',int32_t*)
#define RD_VALUE _IOR('a','b',int32_t*)
 
int main()
{
        int fd;
        int32_t value, number;
        printf("*********************************\n");
        printf("*******WWW.EmbeTronicX.com*******\n");
 
        printf("\nOpening Driver\n");
        fd = open("/dev/etx_device", O_RDWR);
        if(fd < 0) {
                printf("Cannot open device file...\n");
                return 0;
        }
 
        printf("Enter the Value to send\n");
        scanf("%d",&number);
        printf("Writing Value to Driver\n");
        ioctl(fd, WR_VALUE, (int32_t*) &number); 
 
        printf("Reading Value from Driver\n");
        ioctl(fd, RD_VALUE, (int32_t*) &value);
        printf("Value is %d\n", value);
 
        printf("Closing Driver\n");
        close(fd);
}

In case of Makefile is needed:

obj-m += driver.o
 
KDIR = /lib/modules/$(shell uname -r)/build
 
 
all:
    make -C $(KDIR)  M=$(shell pwd) modules
 
clean:
    make -C $(KDIR)  M=$(shell pwd) clean