linux-kernel - Re: [PATCH 1/4] Extend notifier_call_chain to count nr

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Date:	Mon, 20 Nov 2006 22:19:41 -0800
From:	Andrew Morton <akpm@...l.org>
To:	ego@...ibm.com
Cc:	torvalds@...l.org, linux-kernel@...r.kernel.org, vatsa@...ibm.com,
	dipankar@...ibm.com, davej@...hat.com, mingo@...e.hu,
	kiran@...lex86.org
Subject: Re: [PATCH 1/4] Extend notifier_call_chain to count nr_calls made.

On Tue, 14 Nov 2006 17:50:51 +0530
Gautham R Shenoy <ego@...ibm.com> wrote:

> Provide notifier_call_chain with an option to call only a specified number of 
> notifiers and also record the number of call to notifiers made.
> 
> The need for this enhancement was identified in the post entitled 
> "Slab - Eliminate lock_cpu_hotplug from slab" 
> (http://lkml.org/lkml/2006/10/28/92) by Ravikiran G Thirumalai and 
> Andrew Morton.
> 
> This patch adds two additional parameters to notifier_call_chain API namely 
>  - int nr_to_calls : Number of notifier_functions to be called. 
>  		     The don't care value is -1.
> 
>  - unsigned int *nr_calls : Records the total number of notifier_funtions 
> 			    called by notifier_call_chain. The don't care
> 			    value is NULL.
> 
> ...
>
> +
>  static int __kprobes notifier_call_chain(struct notifier_block **nl,
> -		unsigned long val, void *v)
> +					unsigned long val, void *v,
> +					int nr_to_call,	unsigned int *nr_calls)
>  {
>  	int ret = NOTIFY_DONE;
>  	struct notifier_block *nb, *next_nb;
>  
>  	nb = rcu_dereference(*nl);
> -	while (nb) {
> +
> +	while (nb && nr_to_call) {
>  		next_nb = rcu_dereference(nb->next);
>  		ret = nb->notifier_call(nb, val, v);
> +
> +		if (nr_calls)
> +			*nr_calls ++;

This gets

kernel/sys.c: In function 'notifier_call_chain':
kernel/sys.c:164: warning: value computed is not used


And indeed, this code doesn't work.

What happened?

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