linux-kernel - Re: [PATCH] sysctl: allow embedded targets to disable sysctl

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Message-Id: <20080208135816.f242a846.akpm@linux-foundation.org>
Date:	Fri, 8 Feb 2008 13:58:16 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	hs4233@...l.mn-solutions.de, michael-lists@...e-electrons.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysctl: allow embedded targets to disable
 sysctl_check.c

On Fri, 08 Feb 2008 03:36:41 -0700
ebiederm@...ssion.com (Eric W. Biederman) wrote:

> Andrew Morton <akpm@...ux-foundation.org> writes:
> 
> > On Thu, 7 Feb 2008 14:38:58 +0100 Holger Schurig <hs4233@...l.mn-solutions.de>
> > wrote:
> >
> >> Disable sysctl_check.c for embedded targets. This saves about about 11 kB
> >> in .text and another 11 kB in .data on a PXA255 embedded platform.
> >> 
> >
> > Nice improvement.  But iirc sysctl_check was overtly a temporary thing.
> > Eric, was that the intention?
> 
> Well so far sysctl_check has been a remarkably effective little piece of code
> in catching a great many long over looked bugs.
> 
> I do agree that the static tables are big.  My current inclination is to modify
> sys_sysctl so that it does a look up in the binary tables to find the ascii
> names and then sys_sysctl can lookup the information in the ascii tables.
> 
> If we do that we can completely remove ctl_name form the external sysctl data
> structures, which should save us quite a bit of space and make it absolutely
> impossible to add a new binary name.  And with the current ability to compile
> out sys_sysctl the embedded folks would get their space savings.
> 
> I believe the only tricky bit is there are a few places in the network code
> where we need to translate from ifindex to interface name.  Otherwise
> the mapping is fixed.
> 
> No that isn't quite right.  Getting the binary to ascii translation for the
> values is also a bit tricky.
> 
> As for the rest of the checks I don't know if they are that big.  If they
> are then an option to compile them out on embedded platforms where you
> know what you are doing makes sense.  At the same time sysctl has been so
> badly abused in the past, and so very many bugs have been over looked
> that I am extremely reluctant to disable simple sanity checks at
> registration time.
> 
> If we can remove the need for sysctl users to implement the binary
> interface many of those checks go completely away as the reason for their
> existence would be gone.
> 
> I have seen to many absolutely horrible things in the usage of the sysctl
> tables to be happy with an option that removes the sanity checks at this
> point, although the patch likely makes sense from a code size perspective.
> 
> Let's see if we can find a bit of time to make those big tables completely
> specific to sys_sysctl and kill ctl_name in the kernel.  Long term that is
> a whole lot more maintainable, and smaller for everyone who can disable
> sys_sysctl.

mm...  I'm inclined to merge the patch.  It's a decent saving, and it
requires CONFIG_EMBEDDED which most people don't appear to set.

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