usr/sys/conf.h

/*
 * Used to dissect integer device code
 * into major (driver designation) and
 * minor (driver parameter) parts.
 */
struct
{
        char    d_minor;
        char    d_major;
};

/*
 * 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
 * file conf.c.
 */
struct  bdevsw
{
        int     (*d_open)();
        int     (*d_close)();
        int     (*d_strategy)();
        int     *d_tab;
} bdevsw[];

/*
 * 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
 * device numbers.
 */
int     nblkdev;

/*
 * Character device switch.
 */
struct  cdevsw
{
        int     (*d_open)();
        int     (*d_close)();
        int     (*d_read)();
        int     (*d_write)();
        int     (*d_sgtty)();
} cdevsw[];

/*
 * Number of character switch entries.
 * Set by cinit/tty.c
 */
int     nchrdev;