Linux Device Drivers Development

Device number allocation and freeing

Device numbers identify device files across the system. That means there are two ways to allocate these device numbers (actually major and minor):

• Statically: Guessing a major not yet used by another driver using the register_chrdev_region() function. You should avoid using this as much as possible. Its prototype looks this:

   int register_chrdev_region(dev_t first, unsigned int count, \ 
                             char *name); 

This method returns 0 on success, or a negative error code on failure. first is made of the major number that we need along with the first minor of the desired range. You should use MKDEV(ma,mi). count is the number of consecutive device numbers required, and name should be the name of the associated device ...