通过虚拟终端来控制键盘灯

已经有好几个人问过我这个问题了，之前的时候，LKMP中有一个例子来使用定时器在内核态来使得键盘灯闪烁，今天分析了一下那个module代码，发现其使用了ioctl，也就意味着在用户态使用ioctl将会调用驱动中的ioctl，具有一样的效果。

分析一下那个驱动:

/* 
 *  kbleds.c - Blink keyboard leds until the module is unloaded.
 */

#include 
#include 
#include 
#include 		/* For fg_console, MAX_NR_CONSOLES */
#include 		/* For KDSETLED */
#include 	/* For vc_cons */

MODULE_DESCRIPTION("Example module illustrating the use of Keyboard LEDs.");
MODULE_AUTHOR("Daniele Paolo Scarpazza");
MODULE_LICENSE("GPL");

struct timer_list my_timer;
struct tty_driver *my_driver;
char kbledstatus = 0;

#define BLINK_DELAY   HZ/5
#define ALL_LEDS_ON   0x07
#define RESTORE_LEDS  0xFF

/*
 * Function my_timer_func blinks the keyboard LEDs periodically by invoking
 * command KDSETLED of ioctl() on the keyboard driver. To learn more on virtual 
 * terminal ioctl operations, please see file:
 *     /usr/src/linux/drivers/char/vt_ioctl.c, function vt_ioctl().
 *
 * The argument to KDSETLED is alternatively set to 7 (thus causing the led 
 * mode to be set to LED_SHOW_IOCTL, and all the leds are lit) and to 0xFF
 * (any value above 7 switches back the led mode to LED_SHOW_FLAGS, thus
 * the LEDs reflect the actual keyboard status).  To learn more on this, 
 * please see file:
 *     /usr/src/linux/drivers/char/keyboard.c, function setledstate().
 * 
 */

static void my_timer_func(unsigned long ptr)
{
	int *pstatus = (int *)ptr;

	if (*pstatus == ALL_LEDS_ON)
		*pstatus = RESTORE_LEDS;
	else
		*pstatus = ALL_LEDS_ON;

	(my_driver->ioctl) (vc_cons[fg_console].d->vc_tty, NULL, KDSETLED,
			    *pstatus);

	my_timer.expires = jiffies + BLINK_DELAY;
	add_timer(&my_timer);
}

static int __init kbleds_init(void)
{
	int i;

	printk(KERN_INFO "kbleds: loading\n");
	printk(KERN_INFO "kbleds: fgconsole is %x\n", fg_console);
	for (i = 0; i < MAX_NR_CONSOLES; i++) {
		if (!vc_cons[i].d)
			break;
		printk(KERN_INFO "poet_atkm: console[%i/%i] #%i, tty %lx\n", i,
		       MAX_NR_CONSOLES, vc_cons[i].d->vc_num,
		       (unsigned long)vc_cons[i].d->vc_tty);
	}
	printk(KERN_INFO "kbleds: finished scanning consoles\n");

	my_driver = vc_cons[fg_console].d->vc_tty->driver;
	printk(KERN_INFO "kbleds: tty driver magic %x\n", my_driver->magic);

	/*
	 * Set up the LED blink timer the first time
	 */
	init_timer(&my_timer);
	my_timer.function = my_timer_func;
	my_timer.data = (unsigned long)&kbledstatus;
	my_timer.expires = jiffies + BLINK_DELAY;
	add_timer(&my_timer);

	return 0;
}

static void __exit kbleds_cleanup(void)
{
	printk(KERN_INFO "kbleds: unloading...\n");
	del_timer(&my_timer);
	(my_driver->ioctl) (vc_cons[fg_console].d->vc_tty, NULL, KDSETLED,
			    RESTORE_LEDS);
}

module_init(kbleds_init);
module_exit(kbleds_cleanup);

这种方法是通过调用虚拟终端驱动中的ioctl函数，我们完全可以在用户空间open一个虚拟终端，然后对得到的fd进行ioctl。
查找ioctl相关资料，发现ioctl对于虚拟终端fd，支持一个KDSETLED命令字，这样用这个命令字就可以设置三个键盘灯的状态了。
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define ERROR -1

int fd; /* File descriptor for console (/dev/tty/) */

void sighandler(int signum);

void main()
{
    int i;

    /* To be used as the fd in ioctl(). */
    if ((fd = open("/dev/console", O_NOCTTY)) == ERROR) {
        perror("open");
        exit(ERROR);
    }

    signal(SIGINT,  sighandler);
    signal(SIGTERM, sighandler);
    signal(SIGQUIT, sighandler);
    signal(SIGTSTP, sighandler);

    printf("w00w00!\n\n");
    printf("To exit hit Control-C.\n");

    while (1) {
        for (i = 0x01; i <= 0x04; i++) {
            /* We do this because there is no LED for 0x03. */
            if (i == 0x03) continue;

            usleep(50000);

            if ((ioctl(fd, KDSETLED, i)) == ERROR) {
                perror("ioctl");
                close(fd);
                exit(ERROR);
            }
        }
    }

    close(fd);
}

void sighandler(int signum)
{
    /* Turn off all leds. No LED == 0x0. */
    if ((ioctl(fd, KDSETLED, 0x0)) == ERROR) {
        perror("ioctl");
        close(fd);
        exit(ERROR);
    }

    printf("\nw00w00!\n");
    close(fd);
    exit(0);
}

参考:
http://www.net-security.org/article.php?id=83&p=1