[PATCH] net: spider_net: Use struct_size() helper

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

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 spider_net_card {
	...
        struct spider_net_descr darray[0];
};

Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

So, replace the following form:

sizeof(struct spider_net_card) + (tx_descriptors + rx_descriptors) * sizeof(struct spider_net_descr)

with:

struct_size(card, darray, tx_descriptors + rx_descriptors)

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

Building: allmodconfig powerpc.

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/net/ethernet/toshiba/spider_net.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/toshiba/spider_net.c b/drivers/net/ethernet/toshiba/spider_net.c
index 0f346761a2b2..538e70810d3d 100644
--- a/drivers/net/ethernet/toshiba/spider_net.c
+++ b/drivers/net/ethernet/toshiba/spider_net.c
@@ -2311,11 +2311,9 @@ spider_net_alloc_card(void)
 {
 	struct net_device *netdev;
 	struct spider_net_card *card;
-	size_t alloc_size;
 
-	alloc_size = sizeof(struct spider_net_card) +
-	   (tx_descriptors + rx_descriptors) * sizeof(struct spider_net_descr);
-	netdev = alloc_etherdev(alloc_size);
+	netdev = alloc_etherdev(struct_size(card, darray,
+					    tx_descriptors + rx_descriptors));
 	if (!netdev)
 		return NULL;
 
-- 
2.23.0