I am receiving errno 25 in the below code.
Summary of what i have done:

1. Created a module TestCharDriver implementing ioctl. . installed the driver using "insmod"
2. created device node xxx using mknod.
3. created a c program ( below code) .

int main() {

fd = open("/dev/xxx", O_RDWR);
// Not sure about what to be passed as second argument
int returnVal = ioctl(fd,I_FIND,"TestCharDriver");
printf("IOCTL returns %d ERRNO %d\n", returnVal, errno);

close(fd);
return 0;
}

Can anyone explain where i went wrong.

/*********** Below is the code for created module. **************/

struct file_operations xxx_fops =
{
NULL, /* lseek() */
NULL,//xxx_read, /* read() */
NULL, //"xxx_write", /* write() */
NULL, /* readdir() */
NULL, /* select() */
"xxx_ioctl", /* ioctl() */
NULL, /* mmap() */
NULL, //xxx_open, /* open() */
NULL //xxx_close /* close() */
};

int init_module()
{
int returnValue ;
returnValue = register_chrdev(22, "xxx", &xxx_fops) ;
printk(" RETRUN VALUE OF REGISTER %d \n",returnValue);
return 0;
}

int cleanup_module()
{
unregister_chrdev(22,"xxx");
printk("CLEANING MODULES \n");
}

int xxx_ioctl(struct inode * inodearg, struct file * filearg, unsigned int value, unsigned long arg)
{
printk(" IOCTL CALLED FROM USERPROGRAM\n");
}

1) you need to implement open() and close() in addition to ioctl()
2) you don't initialize the file ops structure like that, there is no guarantee to the order of fields in structure, it should be treated as opaque and u use tagged initialization:
and so on.

Thank you, I got that working.