linux-kernel - Re: [PATCH v2] rbd: Remove VLA usage

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Date:   Fri, 16 Mar 2018 09:49:32 +0100
From:   Ilya Dryomov <idryomov@...il.com>
To:     Kyle Spiers <kyle@...ers.me>
Cc:     Sage Weil <sage@...hat.com>, Alex Elder <elder@...nel.org>,
        Ceph Development <ceph-devel@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        "Tobin C. Harding" <me@...in.cc>
Subject: Re: [PATCH v2] rbd: Remove VLA usage

On Fri, Mar 16, 2018 at 5:32 AM, Kyle Spiers <kyle@...ers.me> wrote:
> As part of the effort to remove VLAs from the kernel[1], this moves
> the literal values into the stack array calculation instead of using a
> variable for the sizing. The resulting size can be found from
> sizeof(buf).
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kyle Spiers <kyle@...ers.me>
> ---
>  drivers/block/rbd.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
> index 8e40da0..0e94e1f 100644
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -3100,8 +3100,8 @@ static int __rbd_notify_op_lock(struct rbd_device *rbd_dev,
>  {
>         struct ceph_osd_client *osdc = &rbd_dev->rbd_client->client->osdc;
>         struct rbd_client_id cid = rbd_get_cid(rbd_dev);
> -       int buf_size = 4 + 8 + 8 + CEPH_ENCODING_START_BLK_LEN;
> -       char buf[buf_size];
> +       char buf[4 + 4 + 8 + 8 + CEPH_ENCODING_START_BLK_LEN];

Where is this extra 4 came from?

> +       int buf_size = sizeof(buf)

A semicolon is missing here.  Did you compile this patch?

Thanks,

                Ilya