linux-kernel - Re: [PATCH 04/47] block-rbd: Refactor two calls for memory allocations in rbd_dev_image

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Date:   Tue, 13 Sep 2016 10:03:11 +0200
From:   Ilya Dryomov <idryomov@...il.com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     Ceph Development <ceph-devel@...r.kernel.org>,
        Alex Elder <elder@...nel.org>, Sage Weil <sage@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH 04/47] block-rbd: Refactor two calls for memory
 allocations in rbd_dev_image_id()

On Mon, Sep 12, 2016 at 8:45 PM, SF Markus Elfring
<elfring@...rs.sourceforge.net> wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Sun, 11 Sep 2016 14:48:41 +0200
>
> * Pass the sizes for memory allocations to the corresponding functions
>   directly without storing the calculated values in an
>   intermediate variable.
>
> * Delete the local variable "size" which became unnecessary with
>   this refactoring.
>
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  drivers/block/rbd.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index d61a066..c1da844 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -5833,7 +5833,6 @@ again:
>  static int rbd_dev_image_id(struct rbd_device *rbd_dev)
>  {
>         int ret;
> -       size_t size;
>         char *object_name;
>         void *response;
>         char *image_id;
> @@ -5854,17 +5853,16 @@ static int rbd_dev_image_id(struct rbd_device *rbd_dev)
>          * First, see if the format 2 image id file exists, and if
>          * so, get the image's persistent id from it.
>          */
> -       size = sizeof (RBD_ID_PREFIX) + strlen(rbd_dev->spec->image_name);
> -       object_name = kmalloc(size, GFP_NOIO);
> +       object_name = kmalloc(sizeof(RBD_ID_PREFIX)
> +                             + strlen(rbd_dev->spec->image_name),
> +                             GFP_NOIO);
>         if (!object_name)
>                 return -ENOMEM;
>         sprintf(object_name, "%s%s", RBD_ID_PREFIX, rbd_dev->spec->image_name);
>         dout("rbd id object name is %s\n", object_name);
>
>         /* Response will be an encoded string, which includes a length */
> -
> -       size = sizeof (__le32) + RBD_IMAGE_ID_LEN_MAX;
> -       response = kzalloc(size, GFP_NOIO);
> +       response = kzalloc(sizeof(__le32) + RBD_IMAGE_ID_LEN_MAX, GFP_NOIO);
>         if (!response) {
>                 ret = -ENOMEM;
>                 goto out;
> --
> 2.10.0
>

How is this any better?  If anything, it makes the first kmalloc() call
slightly less readable.

Thanks,

                Ilya