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

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Message-ID: <CAAej5NZZ8NE2Ya4zPC=F3rWEULWXhb1oecp5=1=SEG7Hpqc4NQ@mail.gmail.com>
Date:   Wed, 3 Jun 2020 20:59:32 +0200
From:   Ferenc Fejes <fejes@....elte.hu>
To:     Matthieu Baerts <matthieu.baerts@...sares.net>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        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.

Thanks again for helping me out in this one, I'll be more careful next time!

>
> 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