linux-kernel - Re: [PATCH] block: bio: use struct

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Message-ID: <SN6PR04MB452786C2CE869D353697B9A7860B0@SN6PR04MB4527.namprd04.prod.outlook.com>
Date:   Fri, 17 May 2019 17:18:05 +0000
From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
To:     xiaolinkui <xiaolinkui@...inos.cn>,
        "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: bio: use struct_size() in kmalloc()

Looks good.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@....com>

On 5/17/19 2:17 AM, xiaolinkui wrote:
> 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@...inos.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);