cdev_add — add a char device to the system
| int cdev_add ( | struct cdev * p, | 
| dev_t dev, | |
| unsigned count ); | 
pthe cdev structure for the device
devthe first device number for which this device is responsible
countthe number of consecutive minor numbers corresponding to this device
   cdev_add adds the device represented by p to the system, making it
   live immediately.  A negative error code is returned on failure.