linux-kernel - Re: [PATCH v2 04/35] block: Use kmemdup rather than duplicating its implementation

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Date:   Wed, 03 Jul 2019 12:33:43 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Fuqian Huang <huangfq.daxian@...il.com>
Cc:     Ilya Dryomov <idryomov@...il.com>, Sage Weil <sage@...hat.com>,
        Alex Elder <elder@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        ceph-devel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 04/35] block: Use kmemdup rather than duplicating its
 implementation

On Thu, 2019-07-04 at 00:26 +0800, Fuqian Huang wrote:
> kmemdup is introduced to duplicate a region of memory in a neat way.
> Rather than kmalloc/kzalloc + memcpy, which the programmer needs to
> write the size twice (sometimes lead to mistakes), kmemdup improves
> readability, leads to smaller code and also reduce the chances of mistakes.
> Suggestion to use kmemdup rather than using kmalloc/kzalloc + memcpy.
> 
> Signed-off-by: Fuqian Huang <huangfq.daxian@...il.com>
> ---
> Changes in v2:
>   - Fix a typo in commit message (memset -> memcpy)
> 
>  drivers/block/rbd.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index e5009a34f9c2..47ad3772dc58 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -1068,7 +1068,7 @@ static int rbd_header_from_disk(struct rbd_device *rbd_dev,
>  
>  		if (snap_names_len > (u64)SIZE_MAX)
>  			goto out_2big;
> -		snap_names = kmalloc(snap_names_len, GFP_KERNEL);
> +		snap_names = kmemdup(&ondisk->snaps[snap_count], snap_names_len, GFP_KERNEL);
>  		if (!snap_names)
>  			goto out_err;
>  
> @@ -1088,7 +1088,6 @@ static int rbd_header_from_disk(struct rbd_device *rbd_dev,
>  		 * snap_names_len bytes beyond the end of the
>  		 * snapshot id array, this memcpy() is safe.
>  		 */
> -		memcpy(snap_names, &ondisk->snaps[snap_count], snap_names_len);
>  		snaps = ondisk->snaps;
>  		for (i = 0; i < snap_count; i++) {
>  			snapc->snaps[i] = le64_to_cpu(snaps[i].id);

Reviewed-by: Jeff Layton <jlayton@...nel.org>