netdev - Re: [PATCH] RFC: ipv4: share sysctl net/ipv4/conf/DEVNAME/ tables

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Date:	Sat, 15 Jan 2011 12:41:39 +0200
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Lucian Adrian Grijincu <lucian.grijincu@...il.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	"Pekka Savola (ipv6)" <pekkas@...core.fi>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>,
	Nick Piggin <npiggin@...nel.dk>,
	Al Viro <viro@...iv.linux.org.uk>,
	Christoph Hellwig <hch@....de>,
	Dave Chinner <dchinner@...hat.com>,
	Neil Horman <nhorman@...driver.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Octavian Purdila <opurdila@...acom.com>,
	Vlad Dogaru <ddvlad@...edu.org>
Subject: Re: [PATCH] RFC: ipv4: share sysctl net/ipv4/conf/DEVNAME/ tables

On Sat, Jan 15, 2011 at 04:46:11AM +0200, Lucian Adrian Grijincu wrote:
> To gain access to the name of the directory above a file, sysctl
> handlers are passed an extra argument: the 'struct file*'
> corresponding to the file. From the file we walk up one level to find
> the name of the device. None of the other handlers were changed to
> receive this extra parameter, but due to C's calling convention they
> shouldn't care.

We don't do creepy stuff like that.

I wonder where interactions with device renaming are handled.

> +static int devinet_conf_handler(ctl_table *ctl, int write,
> +				void __user *buffer,
> +				size_t *lenp, loff_t *ppos,
> +				struct file *filp,
> +				proc_handler *proc_handler)
> +{
> +	/* The path to this file is of the form /proc/sys/net/ipv4/conf/$DEVNAME/$CTL
> +	 *
> +	 * To save space, ctl_table is shared between all network
> +	 * devices in the same network namespace, but we need to
> +	 * change the data corresponding to the $DEVNAME network
> +	 * device, not any other's.
> +	 *
> +	 * Use $DEVNAME to obtain the coresponding ipv4_devconf.
> +	 */
> +	struct net *net = ctl->extra2;
> +	const char *dev_name = filp->f_path.dentry->d_parent->d_name.name;
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