[PATCH] Input: gpio_keys_polled - 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 gpio_keys_polled_dev {
        ...
        struct gpio_keys_button_data data[0];
};

size = sizeof(struct gpio_keys_polled_dev) + count * sizeof(struct 
gpio_keys_button_data);
instance = devm_kzalloc(dev, size, 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, data, count), GFP_KERNEL);

Notice that, in this case, variable size is not necessary, hence it
is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gust...@embeddedor.com>
---
 drivers/input/keyboard/gpio_keys_polled.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/input/keyboard/gpio_keys_polled.c 
b/drivers/input/keyboard/gpio_keys_polled.c
index edc7262103b9..c4087be0c2e0 100644
--- a/drivers/input/keyboard/gpio_keys_polled.c
+++ b/drivers/input/keyboard/gpio_keys_polled.c
@@ -235,7 +235,6 @@ static int gpio_keys_polled_probe(struct platform_device 
*pdev)
        struct gpio_keys_polled_dev *bdev;
        struct input_polled_dev *poll_dev;
        struct input_dev *input;
-       size_t size;
        int error;
        int i;
 
@@ -250,9 +249,8 @@ static int gpio_keys_polled_probe(struct platform_device 
*pdev)
                return -EINVAL;
        }
 
-       size = sizeof(struct gpio_keys_polled_dev) +
-                       pdata->nbuttons * sizeof(struct gpio_keys_button_data);
-       bdev = devm_kzalloc(dev, size, GFP_KERNEL);
+       bdev = devm_kzalloc(dev, struct_size(bdev, data, pdata->nbuttons),
+                           GFP_KERNEL);
        if (!bdev) {
                dev_err(dev, "no memory for private data\n");
                return -ENOMEM;
-- 
2.21.0