Re: [PATCH v20] tty: Fix the keyboard led light display problem

[Greg KH]

On Mon, Dec 13, 2021 at 02:12:44PM +0800, lianzhi chang wrote:
> Use the "ctrl+alt+Fn" key combination to switch the system from tty to
> desktop or switch the system from desktop to tty. After the switch is
> completed, it is found that the state of the keyboard lock is
> inconsistent with the state of the keyboard Led light.The reasons are
> as follows:
> 
> * The desktop environment (Xorg and other services) is bound to a tty
>   (assuming it is tty1), and the kb->kbdmode attribute value of tty1
>   will be set to VC_OFF. According to the current code logic, in the
>   desktop environment, the values of ledstate and kb->ledflagstate
>   of tty1 will not be modified anymore, so they are always 0.
> 
> * When switching between each tty, the final value of ledstate set by
>   the previous tty is compared with the kb->ledflagstate value of the
>   current tty to determine whether to set the state of the keyboard
>   light. The process of switching between desktop and tty is also the
>   process of switching between tty1 and other ttys. There are two
>   situations:
> 
>   - (1) In the desktop environment, tty1 will not set the ledstate,
>   which will cause when switching from the desktop to other ttys,
>   if the desktop lights up the keyboard's led, after the switch is
>   completed, the keyboard's led light will always be on;
> 
>   - (2) When switching from another tty to the desktop, this
>   mechanism will trigger tty1 to set the led state. If other tty
>   lights up the led of the keyboard before switching to the desktop,
>   the led will be forcibly turned off. This situation should
>   be avoided.
> 
> * Current patch explanation:When VT is switched,the keyboard LED
>   status will be set to the current tty saved value;the value of
>   kb->kbdledctl can be used to confirm whether the current VT
>   can change the status of the keyboard led light;kb->kbdledctl
>   is a new addition,you can use ioctl get or set.
> 
> Signed-off-by: lianzhi chang <changlianzhi@xxxxxxxxxxxxx>
> Suggested-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> ---
>  
>  v20:
>  New solution: kbd_struct adds a new "kbdledctl" attribute,
>  which can be obtained or changed through ioctl;
>  "kbdledctl" is used to determine whether the current VT
>  can set the keyboard led light;
>  
>  drivers/tty/vt/keyboard.c | 58 +++++++++++++++++++++++++++++++++++++++
>  drivers/tty/vt/vt_ioctl.c | 12 ++++++++
>  include/linux/kbd_kern.h  |  4 +++
>  include/linux/vt_kern.h   |  2 ++
>  include/uapi/linux/kd.h   |  7 ++++-
>  5 files changed, 82 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/vt/keyboard.c b/drivers/tty/vt/keyboard.c
> index c7fbbcdcc346..248c8d790d91 100644
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -153,6 +153,7 @@ static int shift_state = 0;
>  
>  static unsigned int ledstate = -1U;			/* undefined */
>  static unsigned char ledioctl;
> +static bool vt_switch;

This is an odd name for a variable that is there for led issues, right?

>  /*
>   * Notifier list for console keyboard events
> @@ -414,6 +415,12 @@ void vt_set_leds_compute_shiftstate(void)
>  {
>  	unsigned long flags;
>  
> +	/*
> +	 * When switching VT,according to the value of vt_switch,

Extra space after ',' please.

> +	 * judge whether it is necessary to force the keyboard light
> +	 * state to be issued.
> +	 */
> +	vt_switch = true;
>  	set_leds();

How does this new variable have anything to do with the set_leds() call?

>  
>  	spin_lock_irqsave(&kbd_event_lock, flags);
> @@ -1247,14 +1254,24 @@ void vt_kbd_con_stop(unsigned int console)
>   */
>  static void kbd_bh(struct tasklet_struct *unused)
>  {
> +	struct kbd_struct *kb;
>  	unsigned int leds;
>  	unsigned long flags;
>  
> +	kb = kbd_table + fg_console;

So an pointer to an array?  Raw pointer math is odd.

And no bounds checking?

> +	if (kb->kbdledctl == VC_LEDCTL_OFF)
> +		return;

Why exit now?

> +
>  	spin_lock_irqsave(&led_lock, flags);
>  	leds = getleds();
>  	leds |= (unsigned int)kbd->lockstate << 8;
>  	spin_unlock_irqrestore(&led_lock, flags);
>  
> +	if (vt_switch) {
> +		ledstate = ~leds;
> +		vt_switch = false;
> +	}

Please explain what you are doing here with vt_switch.


> +
>  	if (leds != ledstate) {
>  		kbd_propagate_led_state(ledstate, leds);
>  		ledstate = leds;
> @@ -1857,6 +1874,35 @@ int vt_do_kdskbmode(unsigned int console, unsigned int arg)
>  	return ret;
>  }
>  
> +/**
> + *	vt_do_kdskbledctl
> + *	@console: the console to use
> + *	@arg: the requested mode
> + *
> + *	Whether to allow the current vt to change the
> + *	keyboard light
> + */
> +int vt_do_kdskbledctl(unsigned int console, unsigned int arg)
> +{
> +	struct kbd_struct *kb = &kbd_table[console];
> +	int ret = 0;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&kbd_event_lock, flags);
> +	switch (arg) {
> +	case K_LEDCTL_ON:
> +		kb->kbdledctl = VC_LEDCTL_ON;
> +		break;
> +	case K_LEDCTL_OFF:
> +		kb->kbdledctl = VC_LEDCTL_OFF;
> +		break;
> +	default:
> +		ret = -EINVAL;
> +	}
> +	spin_unlock_irqrestore(&kbd_event_lock, flags);
> +	return ret;
> +}
> +
>  /**
>   *	vt_do_kdskbmeta		-	set keyboard meta state
>   *	@console: the console to use
> @@ -2157,6 +2203,18 @@ int vt_do_kdgkbmode(unsigned int console)
>  	}
>  }
>  
> +int vt_do_kdgkbledctl(unsigned int console)
> +{
> +	struct kbd_struct *kb = &kbd_table[console];
> +	/* This is a spot read so needs no locking */

Blank line before comment?

And what do you mean by "spot read"?

> +	switch (kb->kbdledctl) {
> +	case VC_LEDCTL_ON:
> +		return K_LEDCTL_ON;
> +	case VC_LEDCTL_OFF:
> +		return K_LEDCTL_OFF;
> +		}

Why does usespace need to know this value?  What will it do with it?

> +}
> +
>  /**
>   *	vt_do_kdgkbmeta		-	report meta status
>   *	@console: console to report
> diff --git a/drivers/tty/vt/vt_ioctl.c b/drivers/tty/vt/vt_ioctl.c
> index 3639bb6dc372..c78bd452af55 100644
> --- a/drivers/tty/vt/vt_ioctl.c
> +++ b/drivers/tty/vt/vt_ioctl.c
> @@ -405,6 +405,18 @@ static int vt_k_ioctl(struct tty_struct *tty, unsigned int cmd,
>  	case KDGKBMODE:
>  		return put_user(vt_do_kdgkbmode(console), (int __user *)arg);
>  
> +	case KDSKBLEDCTL:
> +		if (!perm)
> +			return -EPERM;
> +		ret = vt_do_kdskbledctl(console, arg);
> +		if (ret)
> +			return ret;
> +		tty_ldisc_flush(tty);
> +		break;
> +
> +	case KDGKBLEDCTL:
> +		return put_user(vt_do_kdgkbledctl(console), (int __user *)arg);
> +
>  	/* this could be folded into KDSKBMODE, but for compatibility
>  	   reasons it is not so easy to fold KDGKBMETA into KDGKBMODE */
>  	case KDSKBMETA:
> diff --git a/include/linux/kbd_kern.h b/include/linux/kbd_kern.h
> index c40811d79769..769b946c2cf9 100644
> --- a/include/linux/kbd_kern.h
> +++ b/include/linux/kbd_kern.h
> @@ -32,6 +32,10 @@ struct kbd_struct {
>  #define VC_CTRLRLOCK	KG_CTRLR 	/* ctrlr lock mode */
>  	unsigned char slockstate; 	/* for `sticky' Shift, Ctrl, etc. */
>  
> +	unsigned char kbdledctl:1； /*Whether to allow to control the led of the keyboard */
> +#define VC_LEDCTL_ON  0	/* VT can set the keyboard light */
> +#define VC_LEDCTL_OFF 1	/* Prohibit VT to set the keyboard light */
> +
>  	unsigned char ledmode:1;
>  #define LED_SHOW_FLAGS 0        /* traditional state */
>  #define LED_SHOW_IOCTL 1        /* only change leds upon ioctl */
> diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
> index b5ab452fca5b..67bdf3eddb5a 100644
> --- a/include/linux/vt_kern.h
> +++ b/include/linux/vt_kern.h
> @@ -149,6 +149,7 @@ void hide_boot_cursor(bool hide);
>  /* keyboard  provided interfaces */
>  int vt_do_diacrit(unsigned int cmd, void __user *up, int eperm);
>  int vt_do_kdskbmode(unsigned int console, unsigned int arg);
> +int vt_do_kdskbledctl(unsigned int console, unsigned int arg);
>  int vt_do_kdskbmeta(unsigned int console, unsigned int arg);
>  int vt_do_kbkeycode_ioctl(int cmd, struct kbkeycode __user *user_kbkc,
>  			  int perm);
> @@ -157,6 +158,7 @@ int vt_do_kdsk_ioctl(int cmd, struct kbentry __user *user_kbe, int perm,
>  int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm);
>  int vt_do_kdskled(unsigned int console, int cmd, unsigned long arg, int perm);
>  int vt_do_kdgkbmode(unsigned int console);
> +int vt_do_kdgkbledctl(unsigned int console);
>  int vt_do_kdgkbmeta(unsigned int console);
>  void vt_reset_unicode(unsigned int console);
>  int vt_get_shift_state(void);
> diff --git a/include/uapi/linux/kd.h b/include/uapi/linux/kd.h
> index ee929ece4112..138d636adf3e 100644
> --- a/include/uapi/linux/kd.h
> +++ b/include/uapi/linux/kd.h
> @@ -86,6 +86,11 @@ struct unimapinit {
>  #define KDGKBMODE	0x4B44	/* gets current keyboard mode */
>  #define KDSKBMODE	0x4B45	/* sets current keyboard mode */
>  
> +#define K_LEDCTL_ON 0x00
> +#define K_LEDCTL_OFF 0x01

As Dan points out, these should be the other way around.

> +#define KDGKBLEDCTL  0x4B73  /* set whether to allow control of keyboard lights */
> +#define KDSKBLEDCTL  0x4B74  /* get whether the keyboard light is currently allowed to be set */

What userspace code is going to use these new ioctls?

I still don't understand the problem that this is supposed to be
solving.  How can we have never had a problem until now with regards to
LED settings on keyboards?  What commit caused this to change?  Has it
always been broken for 30 years and no one noticed?

thanks,

greg k-h