Question

I want to add a char device to /devices in my Linux directory via C code. Since I’m creating fictitious drivers that should only exist when I insmod my_module.ko, I want my module to create a device for me. Below is the part of my code which should add the device, but I only initialize my cdev struct and tell the kernel about it.

int start_mod(void){
    //Because we are dealing with a fictitious device, I want
    //the driver to create my two devices with arbitrarly 
    //assigned major numbers.

    alloc_chrdev_region(&dev_num, FIRST_MINOR, COUNT, DEVICE_NAME); // This assigns my device name
                                    // as well as asign Major # my driver uses

    cdev_init(&(my_dev->my_cdev), &fops);// This initializes my cdev struct that the kernel uses to keep track of my device
    my_dev->my_cdev.owner = THIS_MODULE;
    my_dev->my_cdev.ops = &fops;// fops is my file operations struct

    int err = cdev_add(&(my_dev->my_cdev), dev_num, COUNT);// this in theory should give a pointer to the kernel
    // to my cdev struct that I have setup to exist in my other structure.

    // Now I need to officially add my device to /devices folder.
    return 0;   
}

I’m not to sure what I need to do to officially add the char device to the kernel.

Answer 1

What you do is you use some of the newer registration functions in the kernel like class_create and device_create. This will allow udev to create your device.

Are you saying you wrote a driver without looking at any other drivers?
Because there is no shortage of examples about how to register a character device.

Look in

drivers/char

Those aforementioned functions are GPL-only, by the way, which has implications if you want to redistribute the code.