netdev - Re: [PATCH bpf] bpf: fix unused-var without NETDEVICES

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Date:   Wed, 3 Jun 2020 20:41:25 +0200
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Ferenc Fejes <fejes@....elte.hu>, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: fix unused-var without NETDEVICES

Hi Alexei,

On 03/06/2020 20:14, Alexei Starovoitov wrote:
> On Wed, Jun 03, 2020 at 11:12:01AM +0200, Matthieu Baerts wrote:
>> Hi Ferenc,
>>
>> On 03/06/2020 10:56, Ferenc Fejes wrote:
>>> Matthieu Baerts <matthieu.baerts@...sares.net> ezt írta (időpont:
>>> 2020. jún. 3., Sze, 10:11):
>>>>
>>>> A recent commit added new variables only used if CONFIG_NETDEVICES is
>>>> set.
>>>
>>> Thank you for noticing and fixed this!
>>>
>>>> A simple fix is to only declare these variables if the same
>>>> condition is valid.
>>>>
>>>> Other solutions could be to move the code related to SO_BINDTODEVICE
>>>> option from _bpf_setsockopt() function to a dedicated one or only
>>>> declare these variables in the related "case" section.
>>>
>>> Yes thats indeed a cleaner way to approach this. I will prepare a fix for that.
>>
>> I should have maybe added that I didn't take this approach because in the
>> rest of the code, I don't see that variables are declared only in a "case"
>> section (no "{" ... "}" after "case") and code is generally not moved into a
>> dedicated function in these big switch/cases. But maybe it makes sense here
>> because of the #ifdef!
>> At the end, I took the simple approach because it is for -net.
>>
>> In other words, I don't know what maintainers would prefer here but I am
>> happy to see any another solutions implemented to remove these compiler
>> warnings :)
> 
> since CONFIG_NETDEVICES doesn't change anything in .h
> I think the best is to remove #ifdef CONFIG_NETDEVICES from net/core/filter.c
> and rely on sock_bindtoindex() returning ENOPROTOOPT
> in the extreme case of oddly configured kernels.

Good idea, thank you!
I can send a patch implementing that.

And sorry for the oddly configured kernels :)
It's just used to test the compilation of the code related to MPTCP.

Cheers,
Matt
-- 
Matthieu Baerts | R&D Engineer
matthieu.baerts@...sares.net
Tessares SA | Hybrid Access Solutions
www.tessares.net
1 Avenue Jean Monnet, 1348 Louvain-la-Neuve, Belgium