Linux kernel read custom function - c

Question

Trying to make a read function, that not only adds the numbers together. But also counts how many numbers were added.
Needs to be used in such script:
for i in 1 2 4 8 16 32 64; do
echo $i > /dev/summer0
sleep 60
done
But also just using a test case.
Here is the kernel module code:
/* the memory of the device
*/
int total;
/* Global variables declared as staic, so are global within the file.*/
static char *msg_Ptr;
static char msg[BUF_LEN];
static int n;
/* called after the device is opened
*/
int device_open(struct inode *inode, struct file *file)
{
printk("\nsummer device is open\n");
total = 0;
printk(msg);
msg_Ptr = msg;
return 0;
}
/* Read function */
static ssize_t device_read(struct file *filep, char *buffer, size_t length, loff_t *offset)
{
/* Number of bytes actually written to the buffer */
int bytes_read = 0;
/* If we're at the end of the message, return 0 signifying end of file */
if (*msg_Ptr == 0) return 0;
/* Actually put the data into the buffer */
while (length && *msg_Ptr)
{
/* The buffer is in the user data segment, not the kernel segment;
* assignment won't work. We have to use put_use which copies data from
* the kernel data segment to the user data segment. */
__put_user(*(msg_Ptr++), buffer++);
length++;
n++;
}
/* Most read functions return the number of bytes put into the buffer */
return n;
}
/* handling of ioctl events
*/
long device_ioctl(struct file *file, unsigned int ioctl_num, unsigned long ioctl_param)
{
int number;
switch(ioctl_num)
{
case SUMMER_SET:
__get_user(number, (int*)ioctl_param);
total += number;
break;
case SUMMER_GET:
__put_user(total, (int*)ioctl_param);
break;
}
return 0;
}
/* table of event handlers of the device
*/
struct file_operations fops =
{
read : device_read,
//write : device_write,
open : device_open,
release: device_close,
unlocked_ioctl : device_ioctl
};
As for the testcase
int n;
int main(void)
{
int sum;
char buffer[BUF_LEN];
/* open character device */
int fd = open("/dev/summer0", O_RDWR); // open device
if(fd < 0)
{
printf("no device found\n");
return 0;
}
int nc = read(fd,buffer,4,n);
for(;;)
{
int num;
printf("Number (exit with 0) = ");
while(scanf("%d", &num) != 1)
;
printf("-- %d --\n", num);
if(num <= 0) break;
/* use ioctl to pass a value to the character device */
ioctl(fd, SUMMER_SET, &num);
n++;
}
/* use ioctl to get a value from the character device */
ioctl(fd, SUMMER_GET, &sum);
printf("#char = %d\n", nc);
printf("Result = %d\n", sum);
printf("Buffer: %s\n" , buffer);
close(fd); // close device
return 0;
}
The program is keeping track of the amount of numbers entered during a single test, but it is supposed to keep track of the numbers until I install the kernel module.