linux-kernel - Re: [PATCH 02/31] Constify struct address_space

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Message-ID: <20091205142729.GC9482@parisc-linux.org>
Date:	Sat, 5 Dec 2009 07:27:29 -0700
From:	Matthew Wilcox <matthew@....cx>
To:	Emese Revfy <re.emese@...il.com>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/31] Constify struct address_space_operations for
	2.6.32 v1

On Sat, Dec 05, 2009 at 01:36:56AM +0100, Emese Revfy wrote:
> Matthew Wilcox wrote:
> > On Fri, Dec 04, 2009 at 11:08:09PM +0100, Emese Revfy wrote:
> >> -	int (*writepage)(struct page *page, struct writeback_control *wbc);
> >> +	int (* const writepage)(struct page *page, struct writeback_control *wbc);
> > 
> > Umm.  What effect does this have?
> > What changes as a result of this patch?
> 
> My idea was that since all variables of this type are const, we might
> as well have the compiler enforce it for the future if you think that
> these fields should not be writable at all.

The compiler does already enforce it.  We do it like this:

struct address_space {
        const struct address_space_operations *a_ops;   /* methods */
}

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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