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

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Message-ID: <CAK8P3a11Fkgx-dYXQszOewMacMy9k-SDm9Epu1A6XWE98FcUgQ@mail.gmail.com>
Date:   Tue, 20 Feb 2018 23:08:48 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Daniel Borkmann <daniel@...earbox.net>
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 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.

       Arnd