linux-kernel - Re: [PATCH 28/31] Constify struct super

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Message-ID: <4B1D988E.2000305@gmail.com>
Date:	Tue, 08 Dec 2009 01:06:38 +0100
From:	Emese Revfy <re.emese@...il.com>
To:	Alexey Dobriyan <adobriyan@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 28/31] Constify struct super_operations for 2.6.32 v1

Alexey Dobriyan wrote:
> On 12/6/09, Emese Revfy <re.emese@...il.com> wrote:
>> Alexey Dobriyan wrote:
>>>> -   	struct inode *(*alloc_inode)(struct super_block *sb);
>>>> +   	struct inode *(* const alloc_inode)(struct super_block *sb);
>>> Good rule is if adding const doesn't move object from one section
>>> to another, it isn't worth it.
>>>
>>> I suggest we stick to it or risk another wave of jumbo patches.
>>>
>> If all instances of a given ops structure are const and we would like to
>> preserve this policy for the future as well, then  it is very useful
>> to give future programmers a strong hint about this policy by making
>> the compiler complain about any violation attempts. Otherwise they may
>> very well write code that modifies such structures and we will have to
>> work extra to undo that (or change the policy but in that case it is
>> good to know why we have to do that).
> 
> You may want to look what filesystems do with superblock operations.
> And after super operations were made const writes to it will be caught
> with readonly .rodata config option.
> 
> You're going too far with these modifiers.
> 
> Nothing will be caught.

DEBUG_RODATA catches the unwanted write attempt at runtime whereas
my patch will catch it at compile time. I think it's better to detect
an error as early as possible.
--
Emese
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