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

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Date:   Tue, 20 Feb 2018 23:12:27 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        John Fastabend <john.fastabend@...il.com>,
        Lawrence Brakmo <brakmo@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Networking <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] bpf: hide a possibly unused variable

On 02/20/2018 11:08 PM, Arnd Bergmann wrote:
> On Tue, Feb 20, 2018 at 10:44 PM, Daniel Borkmann <daniel@...earbox.net> wrote:
>> 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.
> 
> Sure, sent a new version now. I decided to clean up that #ifdef
> check as well, since a IS_ENABLED() check is nicer anway.

Looks great, thanks! I'll get it into bpf once the pending pr got pulled.