linux-kernel - Re: [PATCH 1/2] Input: Create input notifier chain in input.c

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Message-ID: <a4zd7uzo3aigyrhturbpgtcsm2slmtqefivky2bfhqiupcc5aj@iorbkwz6ief4>
Date: Wed, 5 Nov 2025 13:55:44 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Jonathan Denose <jdenose@...gle.com>
Cc: Jiri Kosina <jikos@...nel.org>, 
	Benjamin Tissoires <bentiss@...nel.org>, linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] Input: Create input notifier chain in input.c

Hi Jonathan,

On Thu, Oct 30, 2025 at 02:10:40PM +0000, Jonathan Denose wrote:
> To expose input events to other kernel modules, add a blocking notifier
> chain. Publish LID_SWITCH_OPEN/LID_SWITCH_CLOSE events through this
> notifier chain when input_handle_event detects events signaling the lid
> switch has opened or closed.
> 
> Additionally, export a function which allows other kernel modules to
> register notifier_block structs against this notifier chain.
> 
> Signed-off-by: Jonathan Denose <jdenose@...gle.com>
> ---
>  drivers/input/input.c | 13 +++++++++++++
>  include/linux/input.h |  7 +++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/drivers/input/input.c b/drivers/input/input.c
> index a500e1e276c211d1146dbfea421a3402084007f8..b342b1ff138ccc58d4623edcf1152bd85d7054bf 100644
> --- a/drivers/input/input.c
> +++ b/drivers/input/input.c
> @@ -26,6 +26,7 @@
>  #include <linux/kstrtox.h>
>  #include <linux/mutex.h>
>  #include <linux/rcupdate.h>
> +#include <linux/notifier.h>
>  #include "input-compat.h"
>  #include "input-core-private.h"
>  #include "input-poller.h"
> @@ -62,6 +63,8 @@ static const unsigned int input_max_code[EV_CNT] = {
>  	[EV_FF] = FF_MAX,
>  };
>  
> +static struct blocking_notifier_head input_notifier_head;
> +
>  static inline int is_event_supported(unsigned int code,
>  				     unsigned long *bm, unsigned int max)
>  {
> @@ -367,10 +370,20 @@ void input_handle_event(struct input_dev *dev,
>  		if (type != EV_SYN)
>  			add_input_randomness(type, code, value);
>  
> +		if (type == EV_SW && code == SW_LID && !value)
> +			blocking_notifier_call_chain(&input_notifier_head, value ?
> +				LID_SWITCH_CLOSE : LID_SWITCH_OPEN, dev);

I would prefer not having this directly in the input core but rather
have a lid handler that can then use notifier chain to forward the
events further.

Also, here you are running in atomic context, so you need atomic
notifier, not blocking (or you need to involve a workqueue). 

Thanks.

-- 
Dmitry