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

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Date:	Sun, 06 Dec 2009 01:18:30 +0100
From:	Emese Revfy <re.emese@...il.com>
To:	Matthew Wilcox <matthew@....cx>
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

Matthew Wilcox wrote:
> 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 */
> }

This only ensures that the address_space_operations structure cannot be
written through a_ops, but the address_space_operations structure itself
can still be writable. My patch fixes the latter issue.
--
Emese

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