character device driver using MUTEX in linux

MUTEX DRIVER

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/major.h>
#include <linux/capability.h>
#include <asm/uaccess.h>
#include <linux/cdev.h>
#include <linux/vmalloc.h>
#include <linux/ipc.h>
#include <linux/delay.h>
#include <linux/mutex.h>

int i,shmid;
char *a;
struct mutex lock;

static ssize_t sample_char_read(struct file * file, char __user * buf,size_t count, loff_t *ppos)
{
 printk("sample_char2_read size(%ld)\n", count);
 return 0;
}

static ssize_t sample_char_write(struct file *filp, const char *buf,size_t size, loff_t *offp)
{
 //mutex lock
 mutex_lock(&lock);
 printk("sample_char_write size(%ld)\n", size);
 copy_from_user((void *)a,buf,size);
 printk("%s\n",a);
 msleep(3000);
 //mutex unlock
 mutex_unlock(&lock);
 return size;
}

int sample_char_open(struct inode *inode, struct file *filp)
{
 printk("sample_char_open\n");
 //mutex initialization
 mutex_init(&lock);
 a=(void *)vmalloc(20*sizeof(char));
 return 0;
}

int sample_char_release(struct inode *inode, struct file *filp)
{
 printk("sample_char_release\n");
 return 0;
}

static struct file_operations sample_char_fops = {
 read:
 sample_char_read,
 write:
 sample_char_write,
 open:
 sample_char_open,
 release:
 sample_char_release,
};

#define sample_major_number 89
#define max_minors 1

static struct cdev char_cdev;
static dev_t dev;

int init_module(void)
{
 int ret = 0;
 dev = MKDEV(sample_major_number, 0);
 printk("\nLoading the sample char device driver\n");

 ret = register_chrdev_region(dev,1, "sample_char");
 if (ret)
 {
  printk("register_chrdev_region Error\n");
  goto error;
 }

 cdev_init(&char_cdev, &sample_char_fops);
 ret = cdev_add(&char_cdev, dev,2);

 if (ret) {
  printk("cdev_add Error\n");
  goto error_region;
 }

 return 0;
 error_region:
 unregister_chrdev_region(dev, max_minors);
 error:
 return ret;
}

void cleanup_module(void)
{
 cdev_del(&char_cdev);
 unregister_chrdev_region(dev, max_minors);
 printk("\nUnloading the sample char device driver\n");
}


APPLICATION FILE


#include<stdio.h>
#include <fcntl.h>
#include <assert.h>
#include <string.h> // for memset and strlen
#include<sys/types.h>
#include<sys/stat.h>

int main(int argc ,char *argv[])
{
 //
 assert(argc > 1);//abort program if assertion is false
 char buf[100] ;
 char i = 0;
 int g;
 memset(buf, 0, 100);
 printf("Input: %s\n", argv[1]);

 int fp = open("/dev/sample_mutex", O_RDWR);
 if(fp<0)
 {
  perror("not sucess");
 }

 i=fork();
 if(i==0)
 {
  g=write(fp,argv[1], strlen(argv[1]));
 }
 else
 {
  g=write(fp,argv[2], strlen(argv[2]));
  wait(0);
 }
}