[PATCH] i2c: mux: demux-pinctrl: use struct_size() in devm_kzalloc()

[PATCH] i2c: mux: demux-pinctrl: use struct_size() in devm_kzalloc()

[Gustavo A. R. Silva]

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
    int stuff;
    void *entry[];
};

instance = devm_kzalloc(dev, sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = devm_kzalloc(dev, struct_size(instance, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/i2c/muxes/i2c-demux-pinctrl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/muxes/i2c-demux-pinctrl.c b/drivers/i2c/muxes/i2c-demux-pinctrl.c
index 035032e20327..012b45e447c3 100644
--- a/drivers/i2c/muxes/i2c-demux-pinctrl.c
+++ b/drivers/i2c/muxes/i2c-demux-pinctrl.c
@@ -219,8 +219,8 @@ static int i2c_demux_pinctrl_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	priv = devm_kzalloc(&pdev->dev, sizeof(*priv)
-			   + num_chan * sizeof(struct i2c_demux_pinctrl_chan), GFP_KERNEL);
+	priv = devm_kzalloc(&pdev->dev, struct_size(priv, chan, num_chan),
+			    GFP_KERNEL);
 
 	props = devm_kcalloc(&pdev->dev, num_chan, sizeof(*props), GFP_KERNEL);
 
-- 
2.20.1

Re: [PATCH] i2c: mux: demux-pinctrl: use struct_size() in devm_kzalloc()

[Wolfram Sang]

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> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:

I am okay with this patch in general. However, I think the name of the
helper 'struct_size' is a bit unfortunate. I really wondered on the
first read why it needs 3 arguments to find out a struct size. I only
understood on the second read. I think 'trailing_array_struct_size'
would be way more clearer what it does.


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Re: [PATCH] i2c: mux: demux-pinctrl: use struct_size() in devm_kzalloc()

[Peter Rosin]

On 2019-01-04 19:06, Wolfram Sang wrote:
> 
>> Instead of leaving these open-coded and prone to type mistakes, we can
>> now use the new struct_size() helper:
> 
> I am okay with this patch in general. However, I think the name of the
> helper 'struct_size' is a bit unfortunate. I really wondered on the
> first read why it needs 3 arguments to find out a struct size. I only
> understood on the second read. I think 'trailing_array_struct_size'
> would be way more clearer what it does.

I read that as an Acked-by... :-)

Cheers,
Peter

Re: [PATCH] i2c: mux: demux-pinctrl: use struct_size() in devm_kzalloc()

[Wolfram Sang]

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On Sun, Apr 21, 2019 at 06:15:21PM +0000, Peter Rosin wrote:
> On 2019-01-04 19:06, Wolfram Sang wrote:
> > 
> >> Instead of leaving these open-coded and prone to type mistakes, we can
> >> now use the new struct_size() helper:
> > 
> > I am okay with this patch in general. However, I think the name of the
> > helper 'struct_size' is a bit unfortunate. I really wondered on the
> > first read why it needs 3 arguments to find out a struct size. I only
> > understood on the second read. I think 'trailing_array_struct_size'
> > would be way more clearer what it does.
> 
> I read that as an Acked-by... :-)

For this patch, yes. Thanks!


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