linux-kernel - [PATCH] dm-switch: use struct

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Message-ID: <20190108160233.GA20222@embeddedor>
Date:   Tue, 8 Jan 2019 10:02:33 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>, dm-devel@...hat.com
Cc:     linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] dm-switch: use struct_size() in 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;
    void *entry[];
};

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

This code was detected with the help of Coccinelle.

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/md/dm-switch.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/md/dm-switch.c b/drivers/md/dm-switch.c
index fae35caf3672..8a0f057b8122 100644
--- a/drivers/md/dm-switch.c
+++ b/drivers/md/dm-switch.c
@@ -61,8 +61,7 @@ static struct switch_ctx *alloc_switch_ctx(struct dm_target *ti, unsigned nr_pat
 {
 	struct switch_ctx *sctx;
 
-	sctx = kzalloc(sizeof(struct switch_ctx) + nr_paths * sizeof(struct switch_path),
-		       GFP_KERNEL);
+	sctx = kzalloc(struct_size(sctx, path_list, nr_paths), GFP_KERNEL);
 	if (!sctx)
 		return NULL;
 
-- 
2.20.1