linux-kernel - Re: [-mm patch] unexport sys

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Date:	Mon, 10 Sep 2007 13:17:59 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	Al Viro <viro@....linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>, perex@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [-mm patch] unexport sys_{open,read}

On Mon, 10 Sep 2007 21:58:21 +0200 Adrian Bunk <bunk@...nel.org> wrote:

> On Mon, Sep 10, 2007 at 10:25:56AM -0700, Andrew Morton wrote:
> >...
> > Also, Adrian goes on and on with weird theories about how I'm picking on
> > him.  But other patches (such as 7d12e780e003f93433d49ce78c) DO OTHER
> > STUFF.  Like simplify the code, and make it smaller, faster or more
> > maintainable or more reliable.
> 
> The unexport of sys_{open,read} actually makes the kernel smaller...
> 
> > So the tradeoff is quite different from a
> > one-liner which does nothing but kill an export.  And, contrary to his
> > claims, we _do_ put temporary back-compat wrappers in there when we
> > change interfaces on those relatively rare occasions when it is possible,
> > and when we remember to do it.
> 
> Your tradeoff misses the impact on external modules.
> 
> The unexport of sys_open will not break many modules, while
> commit 7d12e780e003f93433d49ce78c most likely broke the majority of 
> external modules.
> 
> Do we guarantee some API stability to module authors or do we not 
> guarantee this?

Neither.  We look at each change and make sensible decisions based upon a
number of factors.

> Emphasizing on API stability in the cases that don't matter much while 
> breaking the API in cases that affect most modules doesn't make any 
> sense at all.
> 
> And your "remember to do it" is an important point. As an example, every 
> change to a struct that is part of the signature of one or exportted 
> functions does change the API of all of these functions. If we offer any 
> API stability for external modules we need to review all patches that 
> touch include/ because many of them contain changes to the modules API 
> that might otherwise get missed.
> 
> Let's either continue to state that their is no stable API for external 
> modules or define some API stability rules and do whatever is required 
> for implementing them.

There is no benefit in making some rigid set of rules.
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