linux-kernel - Re: [PATCH 16/37] drivers/media/video/uvc: Use kmemdup

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Date:	Thu, 20 May 2010 00:09:18 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Julia Lawall <julia@...u.dk>
Cc:	Laurent Pinchart <laurent.pinchart@...net.be>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 16/37] drivers/media/video/uvc: Use kmemdup

Hi Julia,

Thanks for the patch.

On Saturday 15 May 2010 23:17:59 Julia Lawall wrote:
> From: Julia Lawall <julia@...u.dk>
> 
> Use kmemdup when some other buffer is immediately copied into the
> allocated region.
> 
> A simplified version of the semantic patch that makes this change is as
> follows: (http://coccinelle.lip6.fr/)
> 
> // <smpl>
> @@
> expression from,to,size,flag;
> statement S;
> @@
> 
> -  to = \(kmalloc\|kzalloc\)(size,flag);
> +  to = kmemdup(from,size,flag);
>    if (to==NULL || ...) S
> -  memcpy(to, from, size);
> // </smpl>
> 
> Signed-off-by: Julia Lawall <julia@...u.dk>
> 
> ---
>  drivers/media/video/uvc/uvc_driver.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff -u -p a/drivers/media/video/uvc/uvc_driver.c
> b/drivers/media/video/uvc/uvc_driver.c ---
> a/drivers/media/video/uvc/uvc_driver.c
> +++ b/drivers/media/video/uvc/uvc_driver.c
> @@ -637,14 +637,13 @@ static int uvc_parse_streaming(struct uv
>  	}
>  	streaming->header.bControlSize = n;
> 
> -	streaming->header.bmaControls = kmalloc(p*n, GFP_KERNEL);
> +	streaming->header.bmaControls = kmemdup(&buffer[size], p * n,

I'm puzzled, how did the above semantic patch transform 'p*n' into 'p * n' ? 
As a side note, keeping 'p*n' would have allowed the statement to fit in one 
line :-)

> +						GFP_KERNEL);
>  	if (streaming->header.bmaControls == NULL) {
>  		ret = -ENOMEM;
>  		goto error;
>  	}
> 
> -	memcpy(streaming->header.bmaControls, &buffer[size], p*n);
> -
>  	buflen -= buffer[0];
>  	buffer += buffer[0];

-- 
Regards,

Laurent Pinchart
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