linux-kernel - Re: [PATCH 8/8] Re-enable msgmni automatic recomputing msgmni if set to negative

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Message-Id: <20080211122748.64e7bc36.akpm@linux-foundation.org>
Date:	Mon, 11 Feb 2008 12:27:48 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Nadia.Derbey@...l.net
Cc:	linux-kernel@...r.kernel.org, y-goto@...fujitsu.com,
	linux-mm@...ck.org, containers@...ts.linux-foundation.org,
	matthltc@...ibm.com, cmm@...ibm.com, Nadia.Derbey@...l.net
Subject: Re: [PATCH 8/8] Re-enable msgmni automatic recomputing msgmni if
 set to negative

On Mon, 11 Feb 2008 15:16:54 +0100
Nadia.Derbey@...l.net wrote:

> [PATCH 08/08]
> 
> This patch is the enhancement as asked for by Yasunori: if msgmni is set to
> a negative value, register it back into the ipcns notifier chain.
> 
> A new interface has been added to the notification mechanism:
> notifier_chain_cond_register() registers a notifier block only if not already
> registered. With that new interface we avoid taking care of the states changes
> in procfs.
> 
> ...
>
>  static int proc_ipc_callback_dointvec(ctl_table *table, int write,
>  	struct file *filp, void __user *buffer, size_t *lenp, loff_t *ppos)
>  {
> +	struct ctl_table ipc_table;
>  	size_t lenp_bef = *lenp;
>  	int rc;
>  
> -	rc = proc_ipc_dointvec(table, write, filp, buffer, lenp, ppos);
> +	memcpy(&ipc_table, table, sizeof(ipc_table));
> +	ipc_table.data = get_ipc(table);
> +
> +	rc = proc_dointvec(&ipc_table, write, filp, buffer, lenp, ppos);
>  
>  	if (write && !rc && lenp_bef == *lenp)
> -		/*
> -		 * Tunable has successfully been changed from userland:
> -		 * disable its automatic recomputing.
> -		 */
> -		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
> +		tunable_set_callback(*((int *)(ipc_table.data)));
>  
>  	return rc;
>  }
> @@ -119,12 +142,14 @@ static int sysctl_ipc_registered_data(ct
>  	rc = sysctl_ipc_data(table, name, nlen, oldval, oldlenp, newval,
>  		newlen);
>  
> -	if (newval && newlen && rc > 0)
> +	if (newval && newlen && rc > 0) {
>  		/*
> -		 * Tunable has successfully been changed from userland:
> -		 * disable its automatic recomputing.
> +		 * Tunable has successfully been changed from userland
>  		 */
> -		unregister_ipcns_notifier(current->nsproxy->ipc_ns);
> +		int *data = get_ipc(table);
> +
> +		tunable_set_callback(*data);
> +	}
>  
>  	return rc;
>  }

hm, what's happening here?  We take a local copy of the caller's ctl_table
and then pass that into proc_dointvec().  Is that as hacky as it seems??


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