linux-kernel - Re: RFC: kernel coding style: prefer array to &array[0] ?

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Message-ID: <1435791853.12101.131.camel@perches.com>
Date:	Wed, 01 Jul 2015 16:04:13 -0700
From:	Joe Perches <joe@...ches.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Julia Lawall <julia.lawall@...6.fr>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Clemens Ladisch <clemens@...isch.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>
Subject: Re: RFC: kernel coding style: prefer array to &array[0] ?

On Wed, 2015-07-01 at 15:33 -0700, Dmitry Torokhov wrote:
> On Wed, Jul 01, 2015 at 07:53:44AM -0700, Joe Perches wrote:
> > On Wed, 2015-07-01 at 14:26 +0200, Julia Lawall wrote:
> > > On Wed, 1 Jul 2015, Dan Carpenter wrote:
> > > > On Wed, Jul 01, 2015 at 01:54:29PM +0200, Clemens Ladisch wrote:
> > > > > Joe Perches wrote:
> > > > > > It seems most in-kernel uses are 'array' rather than '&array[0]'
> > > > > >
> > > > > > Most of the time, using array is simpler to read than &array[0].
> > > > > >
> > > > > > Exceptions exists when addresses for consecutive members are
> > > > > > used like func(&array[0], &array[1]);
> > > > >
> > > > > I use '&array[0]' when I want to get a pointer to a single object that
> > > > > happens to be the first one in an array.
> > > >
> > > > Yeah.  Of course, you're right.  Otherwise it ends up confusing static
> > > > checkers if you want the first element or the whole array.
> > 
> > Right.
> > 
> > > > > > Should this preference be put into checkpatch and/or CodingStyle?
> > 
> > And checkpatch will have no idea what the prototype
> > for any function is, so this transform is better left
> > for smarter tools like coccinelle.
> > 
> > The proper answer here is no.
[]
> CHECK: Using addressof array 'mtouch->data' index [0] may be simpler as
> 'mtouch->data'
> #97: FILE: drivers/input/touchscreen/mtouch.c:97:
> +       if (MTOUCH_FORMAT_TABLET_STATUS_BIT & mtouch->data[0])

The joys of perl parsing.

> CHECK: Using addressof array 'msg' index [0] may be simpler as 'msg'
> #38: FILE: drivers/input/touchscreen/ipaq-micro-ts.c:38:
> +                                be16_to_cpup((__be16 *) &msg[0]));

That's using the first member in an array.

> I'd be OK with changing cases like:
> 
> CHECK: Using addressof array 'buf' index [0] may be simpler as 'buf'
> #232: FILE: drivers/input/touchscreen/zforce_ts.c:232:
> +       return zforce_send_wait(ts, &buf[0], ARRAY_SIZE(buf));

I think cases like those are sensible to change.

cheers, Joe

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