linux-kernel - [PATCH] eeprom: at24: use struct_size() in devm

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Message-ID: <20190529163052.GA29158@embeddedor>
Date:   Wed, 29 May 2019 11:30:52 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] eeprom: at24: use struct_size() in devm_kzalloc()

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;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
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, entry, count), GFP_KERNEL);

Notice that, in this case, variable at24_size is not necessary, hence it
is removed.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/misc/eeprom/at24.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index ba8e73812644..78ba6b1917a8 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -568,7 +568,6 @@ static int at24_probe(struct i2c_client *client)
 	unsigned int i, num_addresses;
 	struct at24_data *at24;
 	struct regmap *regmap;
-	size_t at24_size;
 	bool writable;
 	u8 test_byte;
 	int err;
@@ -652,8 +651,8 @@ static int at24_probe(struct i2c_client *client)
 	if (IS_ERR(regmap))
 		return PTR_ERR(regmap);
 
-	at24_size = sizeof(*at24) + num_addresses * sizeof(struct at24_client);
-	at24 = devm_kzalloc(dev, at24_size, GFP_KERNEL);
+	at24 = devm_kzalloc(dev, struct_size(at24, client, num_addresses),
+			    GFP_KERNEL);
 	if (!at24)
 		return -ENOMEM;
 
-- 
2.21.0