linux-kernel - Re: [PATCH 4/6] drivers/acpi: Use kasprintf

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Date:	Fri, 19 Mar 2010 00:48:51 +0100 (CET)
From:	Julia Lawall <julia@...u.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Zhang Rui <rui.zhang@...el.com>, Len Brown <lenb@...nel.org>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 4/6] drivers/acpi: Use kasprintf

On Thu, 18 Mar 2010, Andrew Morton wrote:

> On Wed, 10 Mar 2010 22:16:51 +0100 (CET)
> Julia Lawall <julia@...u.dk> wrote:
> 
> > From: Julia Lawall <julia@...u.dk>
> > 
> > kasprintf combines kmalloc and sprintf, and takes care of the size
> > calculation itself.
> > 
> > The semantic patch that makes this change is as follows:
> > (http://coccinelle.lip6.fr/)
> > 
> > // <smpl>
> > @@
> > expression a,flag;
> > expression list args;
> > statement S;
> > @@
> > 
> >   a =
> > -  \(kmalloc\|kzalloc\)(...,flag)
> > +  kasprintf(flag,args)
> >   <... when != a
> >   if (a == NULL || ...) S
> >   ...>
> > - sprintf(a,args);
> > // </smpl>
> > 
> > Signed-off-by: Julia Lawall <julia@...u.dk>
> > 
> > ---
> >  drivers/acpi/video.c |    6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff -u -p a/drivers/acpi/video.c b/drivers/acpi/video.c
> > --- a/drivers/acpi/video.c
> > +++ b/drivers/acpi/video.c
> > @@ -1005,11 +1005,10 @@ static void acpi_video_device_find_cap(s
> >  		result = acpi_video_init_brightness(device);
> >  		if (result)
> >  			return;
> > -		name = kzalloc(MAX_NAME_LEN, GFP_KERNEL);
> > +		name = kasprintf(GFP_KERNEL, "acpi_video%d", count++);
> >  		if (!name)
> >  			return;
> >  
> > -		sprintf(name, "acpi_video%d", count++);
> >  		device->backlight = backlight_device_register(name,
> >  			NULL, device, &acpi_backlight_ops);
> >  		kfree(name);
> > @@ -1056,10 +1055,9 @@ static void acpi_video_device_find_cap(s
> >  		if (device->cap._DCS && device->cap._DSS) {
> >  			static int count;
> >  			char *name;
> > -			name = kzalloc(MAX_NAME_LEN, GFP_KERNEL);
> > +			name = kasprintf(GFP_KERNEL, "acpi_video%d", count++);
> >  			if (!name)
> >  				return;
> > -			sprintf(name, "acpi_video%d", count++);
> >  			device->output_dev = video_output_register(name,
> >  					NULL, device, &acpi_output_properties);
> >  			kfree(name);
> 
> It's not an equivalent change - if the memory allocation fails, this
> patch will now cause `count' to be incremented anyway, presumably
> leaving a gap in the enumeration.

Indeed.  What is below looks better.

julia

> I don't know if that matters.  If so, this:
> 
> --- a/drivers/acpi/video.c~drivers-acpi-use-kasprintf-fix
> +++ a/drivers/acpi/video.c
> @@ -1006,9 +1006,10 @@ static void acpi_video_device_find_cap(s
>  		result = acpi_video_init_brightness(device);
>  		if (result)
>  			return;
> -		name = kasprintf(GFP_KERNEL, "acpi_video%d", count++);
> +		name = kasprintf(GFP_KERNEL, "acpi_video%d", count);
>  		if (!name)
>  			return;
> +		count++;
>  
>  		memset(&props, 0, sizeof(struct backlight_properties));
>  		props.max_brightness = device->brightness->count - 3;
> @@ -1058,9 +1059,10 @@ static void acpi_video_device_find_cap(s
>  		if (device->cap._DCS && device->cap._DSS) {
>  			static int count;
>  			char *name;
> -			name = kasprintf(GFP_KERNEL, "acpi_video%d", count++);
> +			name = kasprintf(GFP_KERNEL, "acpi_video%d", count);
>  			if (!name)
>  				return;
> +			count++;
>  			device->output_dev = video_output_register(name,
>  					NULL, device, &acpi_output_properties);
>  			kfree(name);
> _
> 
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