[PATCH][next] qtnfmac: Use struct_size() in kzalloc()

["Gustavo A. R. Silva" <gustavo@xxxxxxxxxxxxxx>]

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 ieee80211_regdomain {
	...
        struct ieee80211_reg_rule reg_rules[];
};

instance = kzalloc(sizeof(*mac->rd) +
                          sizeof(struct ieee80211_reg_rule) *
                          count, GFP_KERNEL);

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

instance = kzalloc(struct_size(instance, reg_rules, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
 drivers/net/wireless/quantenna/qtnfmac/commands.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/wireless/quantenna/qtnfmac/commands.c b/drivers/net/wireless/quantenna/qtnfmac/commands.c
index 459f6b81d2eb..dc0c7244b60e 100644
--- a/drivers/net/wireless/quantenna/qtnfmac/commands.c
+++ b/drivers/net/wireless/quantenna/qtnfmac/commands.c
@@ -1011,9 +1011,8 @@ qtnf_parse_variable_mac_info(struct qtnf_wmac *mac,
 	if (WARN_ON(resp->n_reg_rules > NL80211_MAX_SUPP_REG_RULES))
 		return -E2BIG;
 
-	mac->rd = kzalloc(sizeof(*mac->rd) +
-			  sizeof(struct ieee80211_reg_rule) *
-			  resp->n_reg_rules, GFP_KERNEL);
+	mac->rd = kzalloc(struct_size(mac->rd, reg_rules, resp->n_reg_rules),
+			  GFP_KERNEL);
 	if (!mac->rd)
 		return -ENOMEM;
 
-- 
2.21.0