Steps to add Linux Character Device Driver

Linux Device driver

Hi we will learn step to add character device driver to Linux

1)      Create Device in /dev

$mknod  /dev/mydev c 200 10

  200- major number ->Driver Identifier

   10-minor number->Device identifier

2)      Change permission if  necessary

$chmod  xxx /dev/mydev

3)      Write Device driver Program

#include <generated/autoconf.h>

#include <linux/module.h>

#include <linux/moduleparam.h>

#include <linux/kernel.h>

#include <linux/init.h>

#include <linux/errno.h>

#include <linux/types.h>

#include <linux/cdev.h>

#include <linux/fs.h>

#include <asm/uaccess.h>

char data[1024];

int mydev_open(struct inode *inode, struct file *filp)

{

   printk(KERN_ALERT "Entering mydev_open\n");

   return 0;

}

ssize_t mydev_read(struct file *filp, char __user *buf, size_t count,

                loff_t *f_pos)

{

   printk(KERN_ALERT "Entering mydev_read\n");

   copy_to_user(buf, data, count);

   return count;

}

ssize_t mydev_write(struct file *filp, const char __user *buf, size_t count,

                loff_t *f_pos)

{

   printk(KERN_ALERT "Entering mydev_write\n");

   copy_from_user(data, buf, count);

   return count;

}

loff_t mydev_llseek(struct file *filp, loff_t off, int whence)

{

   printk(KERN_ALERT "Entering mydev_llseek\n");

   return 0;

}

int mydev_release(struct inode *inode, struct file *filp)

{

   printk(KERN_ALERT "Entering mydev_release\n");

        return 0;

}

struct file_operations mydev_ops = {

   .owner = THIS_MODULE,

   .open = mydev_open,

   .read = mydev_read, 

   .write = mydev_write,

   .llseek = mydev_llseek,

   .release = mydev_release,

};

dev_t devno;

struct cdev cdev;

int mydev_init(void) {

   int res, err;

   int major, minor;

   printk(KERN_ALERT "Starting initialisation\n");

   /* Ask the kernel for a major number */

   res = alloc_chrdev_region(&devno, 10, 1, "mydev");

   if(res < 0) {

         printk(KERN_ALERT "Failed Getting Devno\n");

         return EINVAL;

   }

   major = MAJOR(devno);

   minor = MINOR(devno);

   printk(KERN_ALERT "Got Major No. %d Minor no. %d\n", major, minor);

   /* Tell ther kernel, that these are my functions*/

   cdev_init(&cdev, &mydev_ops);

   err = cdev_add(&cdev, devno, 1);

   if(err) {

         printk(KERN_ALERT "Error in cdev_add \n");

         return EINVAL;

   }

   return 0;

}

void mydev_exit(void ) {

   printk(KERN_ALERT "Finishing: In mydev_exit\n");

   cdev_del(&cdev); 

   unregister_chrdev_region(devno, 1);

}

module_init(mydev_init);

module_exit(mydev_exit);

4)      Write makefile to compile driver program

obj-m += mydev.o

all:

                make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

                #make -C /lib/modules/2.6.39.4/build M=$(PWD) modules

clean:

                #make -C /lib/modules/2.6.39.4/build M=$(PWD) clean

                make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

5)      $make

6)      $insmod  mydev.ko

7)      Write user program using that driver

#include <stdio.h>

#include <fcntl.h>

#include <string.h>

int main() {

                int fd, len;

                char ch[128];

                scanf("%s", ch);

                len = strlen(ch);

                fd = open("/dev/mydev", O_WRONLY);

                printf("Got fd = %d\n", fd);

                write(fd, ch, len -1);

                printf("Got char %s \n", ch);

                close(fd);

                strcpy(ch, "XYZ");

                fd = open("/dev/mydev", O_RDONLY);

                printf("Got fd = %d\n", fd);

                read(fd, ch, len -1 );

                printf("Got char %s \n", ch);

                close(fd);

                return 0;

}

8)       $rmmod mydev 

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