linux-kernel - RE: [PATCH 1/5] arch/arm: Correct NULL test

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Message-ID: <Pine.LNX.4.64.0912281747570.6928@ask.diku.dk>
Date:	Mon, 28 Dec 2009 17:51:15 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, kernel-janitors@...r.kernel.org,
	linux@....linux.org.uk, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: RE: [PATCH 1/5] arch/arm: Correct NULL test

On Mon, 28 Dec 2009, H Hartley Sweeten wrote:

> On Sunday, December 27, 2009 3:08 PM, Julia Lawall wrote:
> >>>  	dbgfs_chan = kmalloc(sizeof(*dbgfs_state) * num_dma_channels,
> >>>  			     GFP_KERNEL);
> >>> -	if (!dbgfs_state)
> >>> +	if (!dbgfs_chan)
> >>>  		goto err_alloc;
> >> Shouldn't the malloc line read:
> >> 
> >> 	... = kmalloc(sizeof(*dbgfs_chan) * ...)
> >> 	                      ^^^^^^^^^^
> >> 
> >> ?
> >
> > Good point, thanks.  I will send a revised patch.
> 
> Wouldn't this be clearer?
> 
> 	... = kmalloc(sizeof(struct dentry) * ...)

Documentation/CodingStyle thinks otherwise:

"The preferred form for passing a size of a struct is the following:

	p = kmalloc(sizeof(*p), ...);

The alternative form where struct name is spelled out hurts readability 
and introduces an opportunity for a bug when the pointer variable type is 
changed but the corresponding sizeof that is passed to a memory allocator 
is not."

And actually, in this case, sizeof(struct dentry) would be wrong, because 
the type of dbgfs_chan is struct dentry **, not struct dentry *.  What is 
wanted is an array of pointers.

julia
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