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लिनक्स/linux-0.01.tar/fs/char dev.c

विकिविश्वविद्यालय से
#include <errno.h>

#include <linux/sched.h>
#include <linux/kernel.h>

extern int tty_read(unsigned minor,char * buf,int count);
extern int tty_write(unsigned minor,char * buf,int count);

static int rw_ttyx(int rw,unsigned minor,char * buf,int count);
static int rw_tty(int rw,unsigned minor,char * buf,int count);

typedef (*crw_ptr)(int rw,unsigned minor,char * buf,int count);

#define NRDEVS ((sizeof (crw_table))/(sizeof (crw_ptr)))

static crw_ptr crw_table[]={
    NULL,        /* nodev */
    NULL,        /* /dev/mem */
    NULL,        /* /dev/fd */
    NULL,        /* /dev/hd */
    rw_ttyx,    /* /dev/ttyx */
    rw_tty,        /* /dev/tty */
    NULL,        /* /dev/lp */
    NULL};        /* unnamed pipes */

static int rw_ttyx(int rw,unsigned minor,char * buf,int count)
{
    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)
{
    if (current->tty<0)
        return -EPERM;
    return rw_ttyx(rw,current->tty,buf,count);
}

int rw_char(int rw,int dev, char * buf, int count)
{
    crw_ptr call_addr;

    if (MAJOR(dev)>=NRDEVS)
        panic("rw_char: dev>NRDEV");
    if (!(call_addr=crw_table[MAJOR(dev)])) {
        printk("dev: %04x\n",dev);
        panic("Trying to r/w from/to nonexistent character device");
    }
    return call_addr(rw,MINOR(dev),buf,count);
}