register_blkdev — register a new block device
| int register_blkdev ( | unsigned int major, | 
| const char * name ); | 
major
     the requested major device number [1..255]. If major=0, try to
     allocate any unused major number.
    
namethe name of the new block device as a zero terminated string
   The name must be unique within the system.
   
   The return value depends on the major input parameter.
   - if a major device number was requested in range [1..255] then the
   function returns zero on success, or a negative error code
   - if any unused major number was requested with major=0 parameter
   then the return value is the allocated major number in range
   [1..255] or a negative error code otherwise