* Used to dissect integer device code
* into major (driver designation) and
* minor (driver parameter) parts.
* Declaration of block device
* switch. Each entry (row) is
* the only link between the
* main unix code and the driver.
* The initialization of the
* device switches is in the
* Nblkdev is the number of entries
* (rows) in the block switch. It is
* set in binit/bio.c by making
* a pass over the switch.
* Used in bounds checking on major
* Character device switch.
* Number of character switch entries.