linux-kernel - Re: [PATCH 1/1] fs/ufs/super.c: remove unnecessary casting

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Date:	Sun, 28 Dec 2014 18:21:58 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Joe Perches <joe@...ches.com>
Cc:	Fabian Frederick <fabf@...net.be>, linux-kernel@...r.kernel.org,
	Evgeniy Dushistov <dushistov@...l.ru>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/1] fs/ufs/super.c: remove unnecessary casting

On Sun, Dec 28, 2014 at 08:45:44AM -0800, Joe Perches wrote:
> On Sun, 2014-12-28 at 15:33 +0000, Al Viro wrote:
> > On Sun, Dec 28, 2014 at 04:28:29PM +0100, Fabian Frederick wrote:
> > > Fix the following coccinelle warning:
> > > fs/ufs/super.c:1418:7-28: WARNING: casting value returned by memory
> > > allocation function to (struct ufs_inode_info *) is useless.
> > 
> > ... except that it makes allocations harder to grep for.
> 
> How does it do that?

search for \<struct[ 	]*$NAME[ 	]*($|[^ 	*]|[*][ 	]*[)])
generally gives a lot of interesting information (variables of that type,
members of anything having that type, sizeof, container_of, explicit casts)
with relatively little noise.

BTW, that's why I really don't like the stuff like
	struct foo *p = kmalloc(sizeof(*p), GFP_KERNEL);
It's bloody hard to spot.

In case of UFS we still catch "sizeof(struct ufs_inode_info)" in
        ufs_inode_cachep = kmem_cache_create("ufs_inode_cache",
                                             sizeof(struct ufs_inode_info),
                                             0, (SLAB_RECLAIM_ACCOUNT|
                                                SLAB_MEM_SPREAD),
                                             init_once);
which gives the obvious secondary search pattern, so it's not _that_ terrible,
but in general it's not something to do without thinking - such a cast could
be placed there exactly to make it stand out on grep.
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