netdev - Re: sysctls

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Date:	Wed, 25 Apr 2007 15:53:19 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, netdev@...r.kernel.org
Subject: Re: sysctls

On Wed, Apr 25, 2007 at 01:45:19PM -0600, Eric W. Biederman wrote:
> Andrew Morton <akpm@...ux-foundation.org> writes:
> 
> > I note that the networking tree is adding new sysctls:
> >
> > <<<<<<< HEAD/include/linux/sysctl.h
> >         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> > =======
> >         NET_IPV6_OPTIMISTIC_DAD=24,
> >         NET_IPV6_ACCEPT_SOURCE_ROUTE=25,
> >>>>>>>> /include/linux/sysctl.h
> >
> > (Well, it's trying to - there are some git rejects in net-2.6.22)
> >
> > But we kind-of decided a while back to stop doing that and to
> > use CTL_UNNUMBERED.
> >
> > Frankly, I don't 100% remember the thinking - Eric, can you please remind
> > us?
> 
> The thinking is this:
> 
>   Binary sysctl numbers are a problem because of patch conflicts like
>   the above, and the related user space breakage they cause.
> 
>   In practice no one uses binary sysctl numbers.
> 
> So the policy should be to add new sysctl's using CTL_UNNUMBERED
> (to prevent patch conflicts and user space breakage).
> 
> There may be cases where someone actually needs the binary sysctl
> interface.  Once there is a demonstrated need we can go back
> and very carefully add numbers for these very few cases, with
> a strong review process.
> 
> Adding binary sysctl numbers should be done as carefully as and with
> as much review as adding syscall numbers, and distro kernels and other
> stable kernels should never get a sysctl number backport until the
> number first reaches Linus's tree.  To avoid difference in meaning
> between different kernels.
> 
> Given that no one except on BSD uses the binary sysctl interface
> anyway my personal preference is to just freeze it and to reduce the
> number of binary sysctls we support if possible.
> 
> Eric
> -
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I did the optimistic dad sysctl, and have no strict use for numbered sysctls (I
was just unaware of the policy).  I'll work up a patch to use
register_sysclt_table with CTL_UNNUMBERED in the next few days.

Regards
Neil

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