To use a character driver, first you should register it with the system. Then you should expose it to the user space.
1. cdev_init and cdev_add functions perform the character device registration. cdev_add adds the character device to the system. When cdev_add function successfully completes, the device is live and the kernel can invoke its operations.2. class_create is used to create a virtual device class, so that in the user space this virtual device node under /dev can be accessed, first of all under the folder sys/class there will have one classfolder under which contains the all specified devices. After this then creating a device and registering it with
sysfs using the device_create function. device_create will create a device file in /dev.more kernel function can refer this link, where all the function and headfile components will be listed.