/* * Structure of a device handler table entry. */struct dev {	int		inuse;			/* In use flag */	int             (*openfnc)();	int             (*closefnc)();	int             (*stratfnc)();          /* Block devs only */	int             (*rd_fnc)();            /* Char devs only */	int             (*wr_fnc)();            /* Char devs only */	int		(*sig_fnc)();		/* Signal device (interrupt) */};# define        NULLDEV         (( int (*)()) '\0')# define        ioctlfnc        stratfnc/* * Mention device switches. */extern struct dev bdevsw[];extern struct dev cdevsw[];