linux-kernel - Re: [PATCH 0/5] net: sysctl: share ipv4/ipv6 sysctl tables

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Date:	Fri, 4 Feb 2011 12:49:41 +0200
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Lucian Adrian Grijincu <lucian.grijincu@...il.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Octavian Purdila <opurdila@...acom.com>
Subject: Re: [PATCH 0/5] net: sysctl: share ipv4/ipv6 sysctl tables

On Fri, Feb 4, 2011 at 6:37 AM, Lucian Adrian Grijincu
<lucian.grijincu@...il.com> wrote:
> Each network device gets the same 25/24 sysctl entries for ipv4/ipv6
> in /proc/sys/net/ipv4/conf/DEVNAME and /proc/sys/net/ipv6/conf/DEVNAME
>
> Unfortunately, space is wasted holding very much similar data.
> Fortunately, with some tricks these entries can be shared between all
> network devices.
>
>
> The single entry in 'struct ctl_table' that was modified at runtime
> for leaf ctl_table nodes and prevented sharing was 'parent'. This
> field was first introduces for selinux and then was used to implement
> sysctl_check_table. Selinux recently removed the need for this field:
> * http://thread.gmane.org/gmane.linux.kernel.lsm/12623
> * LKML-Reference: 1296519474-15714-1-git-send-email-lucian.grijincu@...il.com
>
>
> Remove the need for 'parent' in sysctl_check_table and remove the
> 'parent' field:
>
>  [PATCH 1/5] sysctl: faster reimplementation of sysctl_check_table
>  [PATCH 2/5] sysctl: remove useless ctl_table->parent field
>
>
> Pave the way for sharing of ipv4/6 tables: allow data to be stored in
> the nodes above the leafs that will be shared:
>
>  [PATCH 3/5] sysctl: write ctl_table->extra2 to entries created from ctl_path
>
>
> Finally share the leaf sysctl tables for ipv4/ipv6:
>
>  [PATCH 4/5] ipv4: share sysctl net/ipv4/conf/DEVNAME/ tables
>  [PATCH 5/5] ipv6: share sysctl net/ipv6/conf/DEVNAME/ tables

Meh.

First you remove ->parent, then heroically pass "struct file *"
to sysctl handlers which duplicates all information already passed
and brings dcache into picture.

Binary sysctl rewrite confused you into thinking that d_name.name
is the way, but it isn't.
For binary sysctl(2) you wouldn't get d_name.name.
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