linux-kernel - Re: [PATCH 0/1] Constify struct address_space

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Message-ID: <20091216080653.GU24406@elf.ucw.cz>
Date:	Wed, 16 Dec 2009 09:06:53 +0100
From:	Pavel Machek <pavel@....cz>
To:	Emese Revfy <re.emese@...il.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	Matthew Wilcox <matthew@....cx>, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 0/1] Constify struct address_space_operations for
 2.6.32-git-053fe57ac v2

Hi!

> > One const in structure declaration seems to be just enough, see:
> > 
> > const struct a {
> > 	void (* f)(void);
> > 	void (* const g)(void);
> > } s;
> > 
> > void h(void)
> > {
> > 	struct a *p = &s;
> > 	s.f = 0;
> > 	s.g = 0;
> > 	p->f = 0;
> > 	p->g = 0;
> > }
> > 
> > 
> > delme.c: In function 'h':
> > delme.c:8: warning: initialization discards qualifiers from pointer target type
> > delme.c:9: error: assignment of read-only variable 's'
> > delme.c:10: error: assignment of read-only variable 's'
> > delme.c:12: error: assignment of read-only member 'g'
> > 
> > You get clean-enough warnings.
> 
> Notice how you got an error for line 12 (p->g assignment) but no warning or error
> at all for line 11 (p->f assignment). This example illustrates what I was explaining
> so far:

And notice how you get warning for line 8? That's what I'm talking
about, and it should be enough to make the developer think about what
he's doing. 
									Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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