Device Driver: Char Driver part 1 -> Kernel and Application Program for file handling

Tutorial :

Program in a KERNEL to be use by user for open,close,read and write, along with the USER program to access Kernel program, with make file.

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/* Program to make a kernel to be accessed by the user */
#include<linux/module.h>
#include<linux/kernel.h>
#include<linux/kdev_t.h>
#include<linux/fs.h>
#include<linux/cdev.h>
#include<asm/uaccess.h>
MODULE_LICENSE("GPL");
struct cdev rss_str;
int major=0;
int minor=0;
dev_t rss;
void rss_reg();
static int rss_init()
{
printk("intializing module\n");
rss_reg();
return 0; }
static void rss_release()
{
printk("Exiting module\n");
cdev_del(&rss_str);
unregister_chrdev_region(rss,1);
}
// READ file

ssize_t rss_read(struct file *rss_str,char *rssuserbuff,size_t rssnumbytes,loff_t *rss_off)
{
  char buff[]="NOIDA\0";
printk("Reading:\n");
copy_to_user(rssuserbuff,buff,6);
   return 6;
}
// Write file
ssize_t rss_write(struct file *rss_str,const char * rssuserbuff, size_t rssnumbytes, loff_t *rss_off)
{
char buff[]="NOIDA\0";
        printk("writing:\n");
        copy_from_user(rssuserbuff,buff,6);
printk("%s\n",buff);
        return 6;
}

//open file
int rss_open(struct inode *rss_str, struct file rss_file)
{ printk("opening:\n");
  return 0;
}
//close file int rss_close(struct inode *rss_str, struct file rss_file)
{        printk("closing:\n");
        return 0;
}
struct file_operations rss_fops={
.owner=THIS_MODULE,
.read=rss_read,
.write=rss_write,
.open=rss_open,
.release=rss_close,
};

void rss_reg()
{
int res,num;
res=alloc_chrdev_region(&rss,0,1,"rss");
if(res<0)
printk("Registration Failed.... \n");
major=MAJOR(rss);
minor=MINOR(rss);
printk("Major no = %d  \n",major);
printk("Minor no = %d  \n",minor);
num=MKDEV(major,minor);
printk("Device no = %d  \n",num);
cdev_init(&rss_str,&rss_fops);
rss_str.owner=THIS_MODULE;
cdev_add(&rss_str,num,1);
}
module_init(rss_init);
module_exit(rss_release);

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User Program:

#include<stdio.h>

#include<fcntl.h>

#include<sys/types.h>

#include<sys/stat.h>

main()

{

int fd;

char  ubuff[80]="hai hello world", kbuff[80];

fd = open ("/dev/rss", O_RDWR , 0777 ) ;

if (fd <0 )

{

printf("error in opening file\n");

exit (-1 ) ;

}

if(write ( fd, ubuff, 6 ) < 0)

printf("can't write\n");

if(read (fd, kbuff,100 )<0)

printf("can't read\n") ;

printf ("\n Kernel Data: %s", kbuff);

close(fd);

return 0 ;

}

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Make File

obj-m:=rss.o

KERNELDIR=/lib/modules/$(shell uname -r)/build

all:

make -C $(KERNELDIR) M=$(shell pwd) modules

clean:

make -C $(KERNELDIR) M=$(shell pwd) clean