netdev - Re: [PATCH] bpf: hide a possibly unused variable

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Date:   Tue, 20 Feb 2018 22:44:29 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Arnd Bergmann <arnd@...db.de>, Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Lawrence Brakmo <brakmo@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: hide a possibly unused variable

Hi Arnd,

On 02/20/2018 10:16 PM, Arnd Bergmann wrote:
> The only user of this variable is inside of an #ifdef, causing
> a warning without CONFIG_INET:
> 
> net/core/filter.c: In function '____bpf_sock_ops_cb_flags_set':
> net/core/filter.c:3382:6: error: unused variable 'val' [-Werror=unused-variable]
>   int val = argval & BPF_SOCK_OPS_ALL_CB_FLAGS;
> 
> This adds the same #ifdef around the declaration.
> 
> Fixes: b13d88072172 ("bpf: Adds field bpf_sock_ops_cb_flags to tcp_sock")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  net/core/filter.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 08ab4c65a998..c3dc6d60b4bb 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3379,7 +3379,9 @@ BPF_CALL_2(bpf_sock_ops_cb_flags_set, struct bpf_sock_ops_kern *, bpf_sock,
>  	   int, argval)
>  {
>  	struct sock *sk = bpf_sock->sk;
> +#ifdef CONFIG_INET
>  	int val = argval & BPF_SOCK_OPS_ALL_CB_FLAGS;
> +#endif

Looks good, thanks for the fix!

Could you move the existing '#ifdef CONFIG_INET' to the beginning of
the function given the only error in case of !CONFIG_INET is -EINVAL
anyway? That would at least not increase the ifdef ugliness further.

Thanks a lot,
Daniel

>  	if (!sk_fullsock(sk))
>  		return -EINVAL;
>