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Date:   Wed, 3 Jun 2020 11:14:55 -0700
From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
To:     Matthieu Baerts <matthieu.baerts@tessares.net>
Cc:     Ferenc Fejes <fejes@inf.elte.hu>, netdev@vger.kernel.org,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf] bpf: fix unused-var without NETDEVICES
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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@tessares.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.