/* *  linux/fs/char_dev.c * *  (C) 1991  Linus Torvalds */#include <errno.h>#include <sys/types.h>#include <linux/sched.h>#include <linux/kernel.h>#include <asm/segment.h>#include <asm/io.h>extern int tty_read(unsigned minor,char * buf,int count);extern int tty_write(unsigned minor,char * buf,int count);typedef (*crw_ptr)(int rw,unsigned minor,char * buf,int count,off_t * pos);static int rw_ttyx(int rw,unsigned minor,char * buf,int count,off_t * pos){	return ((rw==READ)?tty_read(minor,buf,count):		tty_write(minor,buf,count));}static int rw_tty(int rw,unsigned minor,char * buf,int count, off_t * pos){	if (current->tty<0)		return -EPERM;	return rw_ttyx(rw,current->tty,buf,count,pos);}static int rw_ram(int rw,char * buf, int count, off_t *pos){	return -EIO;}static int rw_mem(int rw,char * buf, int count, off_t * pos){	return -EIO;}static int rw_kmem(int rw,char * buf, int count, off_t * pos){	return -EIO;}static int rw_port(int rw,char * buf, int count, off_t * pos){	int i=*pos;	while (count-->0 && i<65536) {		if (rw==READ)			put_fs_byte(inb(i),buf++);		else			outb(get_fs_byte(buf++),i);		i++;	}	i -= *pos;	*pos += i;	return i;}static int rw_memory(int rw, unsigned minor, char * buf, int count, off_t * pos){	switch(minor) {		case 0:			return rw_ram(rw,buf,count,pos);		case 1:			return rw_mem(rw,buf,count,pos);		case 2:			return rw_kmem(rw,buf,count,pos);		case 3:			return (rw==READ)?0:count;	/* rw_null */		case 4:			return rw_port(rw,buf,count,pos);		default:			return -EIO;	}}#define NRDEVS ((sizeof (crw_table))/(sizeof (crw_ptr)))static crw_ptr crw_table[]={	NULL,		/* nodev */	rw_memory,	/* /dev/mem etc */	NULL,		/* /dev/fd */	NULL,		/* /dev/hd */	rw_ttyx,	/* /dev/ttyx */	rw_tty,		/* /dev/tty */	NULL,		/* /dev/lp */	NULL};		/* unnamed pipes */int rw_char(int rw,int dev, char * buf, int count, off_t * pos){	crw_ptr call_addr;	if (MAJOR(dev)>=NRDEVS)		return -ENODEV;	if (!(call_addr=crw_table[MAJOR(dev)]))		return -ENODEV;	return call_addr(rw,MINOR(dev),buf,count,pos);}