how to write a shell script which communicates with the kernel module - c

Question

Below is my kernel module,which I tested through C program but now instead of using c application I want to write a shell script which do read and write operation with my kernel module ?
Thanks in advance.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <asm/uaccess.h>
#define DEVICE_NAME "mydevice"
#define CLASS_NAME "device"
MODULE_LICENSE("GPL");
MODULE_AUTHOR("ABC");
MODULE_DESCRIPTION("A simple Linux character driver");
MODULE_VERSION("0.1");
static int majorNumber;
static char message[256] = {0};
static short size_of_message;
static int numberOpens = 0;
static struct class* character_deviceClass = NULL;
static struct device* character_deviceDevice = NULL;
static int dev_open(struct inode *, struct file *);
static int dev_release(struct inode *, struct file *);
static ssize_t dev_read(struct file *, char *, size_t, loff_t *);
static ssize_t dev_write(struct file *, const char *, size_t, loff_t *);
static DEFINE_MUTEX(devicedev_mutex);
static struct file_operations fops =
{
.open = dev_open,
.read = dev_read,
.write = dev_write,
.release = dev_release,
};
static int __init character_device_init(void){
printk(KERN_INFO "Shell: Initializing the character device LKM\n");
majorNumber = register_chrdev(0, DEVICE_NAME, &fops);
if (majorNumber<0){
printk(KERN_ALERT "character device failed to register a major number\n");
return majorNumber;
}
printk(KERN_INFO "character device: registered correctly with major number %d\n", majorNumber);
character_deviceClass = class_create(THIS_MODULE, CLASS_NAME);
if (IS_ERR(character_deviceClass)){
unregister_chrdev(majorNumber, DEVICE_NAME);
printk(KERN_ALERT "Failed to register device class\n");
return PTR_ERR(character_deviceClass);
}
printk(KERN_INFO "character device: device class registered correctly\n");
character_deviceDevice = device_create(character_deviceClass, NULL, MKDEV(majorNumber, 0), NULL, DEVICE_NAME);
if (IS_ERR(character_deviceDevice)){
class_destroy(character_deviceClass);
unregister_chrdev(majorNumber, DEVICE_NAME);
printk(KERN_ALERT "Failed to create the device\n");
return PTR_ERR(character_deviceDevice);
}
printk(KERN_INFO "character device: device class created correctly\n");
mutex_init(&devicedev_mutex);
return 0;
}
static void __exit character_device_exit(void){
mutex_destroy(&devicedev_mutex);
device_destroy(character_deviceClass, MKDEV(majorNumber, 0));
class_unregister(character_deviceClass);
class_destroy(character_deviceClass);
unregister_chrdev(majorNumber, DEVICE_NAME);
printk(KERN_INFO "character device: Goodbye from the LKM!\n");
}
static int dev_open(struct inode *inodep, struct file *filep){
if(!mutex_trylock(&devicedev_mutex))
{
printk(KERN_ALERT "Character device: Device in use by another process");
return -EBUSY;
}
numberOpens++;
printk(KERN_INFO "character device: Device has been opened %d time(s)\n", numberOpens);
return 0;
}
static ssize_t dev_read(struct file *filep, char *buffer, size_t len, loff_t *offset){
int error_count = 0;
error_count = copy_to_user(buffer, message, size_of_message);
if (error_count==0){
printk(KERN_INFO "character device: Sent %d characters to the user\n", size_of_message);
return (size_of_message=0);
}
else {
printk(KERN_INFO "character device: Failed to send %d characters to the user\n", error_count);
return -EFAULT;
}
}
static ssize_t dev_write(struct file *filep, const char *buffer, size_t len, loff_t *offset){
sprintf(message, "%s(%d letters)", buffer, len);
size_of_message = strlen(message);
printk(KERN_INFO "character device: Received %d characters from the user\n", len);
return len;
}
static int dev_release(struct inode *inodep, struct file *filep){
mutex_unlock(&devicedev_mutex);
printk(KERN_INFO "character device: Device successfully closed\n");
return 0;
}
module_init(character_device_init);
module_exit(character_device_exit);

Answer 1

Let's say that you registered with major number 254 and minor number 1 (the actual code given in your question logs the allocated numbers to dmesg, so check there). If you didn't have udev or similar configured to create a /dev/mydevice for you, you could do so yourself:
mknod /dev/mydevice c 254 1 # substitute the real allocated values
At that point, opening it is the same as with anything else:
# file descriptor number 3 is arbitrary, but the same number needs to be reused later
# don't use 0-2, which are reserved for stdin/stdout/stderr
exec 3<>/dev/mydevice
...and reads and writes are similarly conventional:
echo "This is a write" >&3
read varname <&3 # read until newline from device