Making a character device driver in linux system

For making a device driver:
we need to make a virtual drive, a driver (a module to say how to read the drive), a user space code to access the drive.

At first, we need to have a complete linux kernel installed in our system. We can find a list of kernel here: https://www.kernel.org/
For example, We installed linux 4.1.45
command:

$ wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.1.46.tar.xz 

There is a project in gitHub that can help you to understand the process of making character device driver.

Link: https://github.com/coderashis/OperatingSystem/tree/master/path_read_using_driver

The following steps would help you to run the project:

 --------- Making a drive: (as a file)
To achieve this, a file (which will be used as the device driver) need to create typing the following command as root:

$ sudo mknod /dev/path_reader_driver c 248 0

In the above, c means that a char device is to be created, 248 is the major number and 0 is the minor number. 
Major number is used for kernel to link the file with a driver/module.

It’s also convenient to unprotect the device:
$ sudo chmod 666 /dev/path_reader_driver

--------- Making a driver:
- To make a driver, we made a kernel module code that has file structure (read, write methods...) for access. The file is path_reader_driver.c. 
- Keep path_reader_driver and Makefile in same folder.
Now, you can go to the file folder and run make file.
$ make

You will find there is one .ko file. It is a kernel object file. Now, to add this module in your system, you need to attach it as a root user.

$ sudo insmod path_reader_driver.ko

--------- Making a userspace code:
Our input_read.c is userspace code that will try to access driver as a file ( open("/dev/path_reader_driver","r"))


After completing our task, it is important to remove the module
$sudo rmmod path_reader_driver.ko

To display your module, use the following command:
$ lsmod