linux-kernel - Re: CTL_UNNUMBERED (Re: [PATCH] 9p: Don't use binary sysctl numbers.)

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Date:	Tue, 24 Jul 2007 00:28:36 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Latchesar Ionkov <lucho@...kov.net>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: CTL_UNNUMBERED (Re: [PATCH] 9p: Don't use binary sysctl numbers.)

On Sat, Jul 21, 2007 at 04:36:03PM -0600, Eric W. Biederman wrote:
> Alexey Dobriyan <adobriyan@...il.com> writes:
> > That's separate patch but CTL_UNNUMBERED must die, because it's totally
> > unneeded. If you don't want sysctl(2) interface just SKIP ->ctl_name
> > initialization and save one line for something useful.

[9p and .ctl_name]

> Now to the issue of using CTL_UNNUMBERED versus knowing that the magic
> value is zero and we can just leave it uninitialized.  I don't much
> care but given how often people who are not actively watching this
> mess up I tend to prefer the explicit value.

mmm, from my own experience the quickest way to add sysctl to kernel is
to _copy_ from other place and tweak variable name and string itself.
I'm sure that's what evebody is doing.

And once you're copy-pasting, existence of CTL_UNNUMBERED or absence of
it doesn't matter. Propagating of CTL_UNNUMBERED or empty .ctl_name
depends entirely on the place from where you're copy-pasting.

And since it doesn't matter, we'd better save one line :)

> It is a practical
> question of how do we get the word out that we should not expand the
> binary interface anymore.

Article on LWN, scary comment near struct ctl_table::ctl_name, tree-wide
removal .ctl_name initializers, periodic grepping of -mm and -rc diffs.
I promise to grep next -mm patch and submit CTL_UNNUMBERED removal :)

> The only really practical way I can see us doing better then we are
> today is to have a separate tree that maps binary numbers into ascii
> strings and so we remove the ctl_name field entirely from ctl_table.

Not sure how to do this cleanly and without flag-day. And it's
additional code.

> That way people attempting to assign binary numbers using old
> conventions will have code that doesn't even compile, and the
> developers themselves are more likely to spot the problem.

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