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From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
To:     xiaolinkui <xiaolinkui@kylinos.cn>,
        "axboe@kernel.dk" <axboe@kernel.dk>
CC:     "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] block: bio: use struct_size() in kmalloc()
Thread-Topic: [PATCH] block: bio: use struct_size() in kmalloc()
Thread-Index: AQHVDJFi2AQuSKSW70u18m79g25Ygg==
Date:   Fri, 17 May 2019 17:18:05 +0000
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Looks good.=0A=
=0A=
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>=0A=
=0A=
On 5/17/19 2:17 AM, xiaolinkui wrote:=0A=
> One of the more common cases of allocation size calculations is finding=
=0A=
> the size of a structure that has a zero-sized array at the end, along=0A=
> with memory for some number of elements for that array. For example:=0A=
>=0A=
> struct foo {=0A=
>     int stuff;=0A=
>     struct boo entry[];=0A=
> };=0A=
>=0A=
> instance =3D kmalloc(sizeof(struct foo) + count * sizeof(struct boo), GFP=
_KERNEL);=0A=
>=0A=
> Instead of leaving these open-coded and prone to type mistakes, we can=0A=
> now use the new struct_size() helper:=0A=
>=0A=
> instance =3D kmalloc(struct_size(instance, entry, count), GFP_KERNEL);=0A=
>=0A=
> Signed-off-by: xiaolinkui <xiaolinkui@kylinos.cn>=0A=
> ---=0A=
>  block/bio.c | 7 ++-----=0A=
>  1 file changed, 2 insertions(+), 5 deletions(-)=0A=
>=0A=
> diff --git a/block/bio.c b/block/bio.c=0A=
> index 683cbb4..847ac60 100644=0A=
> --- a/block/bio.c=0A=
> +++ b/block/bio.c=0A=
> @@ -436,9 +436,7 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask, unsigned=
 int nr_iovecs,=0A=
>  		if (nr_iovecs > UIO_MAXIOV)=0A=
>  			return NULL;=0A=
>  =0A=
> -		p =3D kmalloc(sizeof(struct bio) +=0A=
> -			    nr_iovecs * sizeof(struct bio_vec),=0A=
> -			    gfp_mask);=0A=
> +		p =3D kmalloc(struct_size(bio, bi_io_vec, nr_iovecs), gfp_mask);=0A=
>  		front_pad =3D 0;=0A=
>  		inline_vecs =3D nr_iovecs;=0A=
>  	} else {=0A=
> @@ -1120,8 +1118,7 @@ static struct bio_map_data *bio_alloc_map_data(stru=
ct iov_iter *data,=0A=
>  	if (data->nr_segs > UIO_MAXIOV)=0A=
>  		return NULL;=0A=
>  =0A=
> -	bmd =3D kmalloc(sizeof(struct bio_map_data) +=0A=
> -		       sizeof(struct iovec) * data->nr_segs, gfp_mask);=0A=
> +	bmd =3D kmalloc(struct_size(bmd, iov, data->nr_segs), gfp_mask);=0A=
>  	if (!bmd)=0A=
>  		return NULL;=0A=
>  	memcpy(bmd->iov, data->iov, sizeof(struct iovec) * data->nr_segs);=0A=
=0A=
=0A=