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From:   xiaolinkui <xiaolinkui@kylinos.cn>
To:     axboe@kernel.dk
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        xiaolinkui@kylinos.cn
Subject: [PATCH] block: bio: use struct_size() in kmalloc()
Date:   Fri, 17 May 2019 17:12:30 +0800
Message-Id: <1558084350-25632-1-git-send-email-xiaolinkui@kylinos.cn>
Feedback-ID: bizesmtp:kylinos.cn:qybgforeign:qybgforeign4
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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[];
};

instance = kmalloc(sizeof(struct foo) + count * sizeof(struct boo), GFP_KERNEL);

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

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

Signed-off-by: xiaolinkui <xiaolinkui@kylinos.cn>
---
 block/bio.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 683cbb4..847ac60 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -436,9 +436,7 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned int nr_iovecs,
 		if (nr_iovecs > UIO_MAXIOV)
 			return NULL;
 
-		p = kmalloc(sizeof(struct bio) +
-			    nr_iovecs * sizeof(struct bio_vec),
-			    gfp_mask);
+		p = kmalloc(struct_size(bio, bi_io_vec, nr_iovecs), gfp_mask);
 		front_pad = 0;
 		inline_vecs = nr_iovecs;
 	} else {
@@ -1120,8 +1118,7 @@ static struct bio_map_data *bio_alloc_map_data(struct iov_iter *data,
 	if (data->nr_segs > UIO_MAXIOV)
 		return NULL;
 
-	bmd = kmalloc(sizeof(struct bio_map_data) +
-		       sizeof(struct iovec) * data->nr_segs, gfp_mask);
+	bmd = kmalloc(struct_size(bmd, iov, data->nr_segs), gfp_mask);
 	if (!bmd)
 		return NULL;
 	memcpy(bmd->iov, data->iov, sizeof(struct iovec) * data->nr_segs);
-- 
2.7.4