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

From: Matthieu Baerts <matthieu.baerts@tessares.net>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
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
Date: Wed, 3 Jun 2020 20:41:25 +0200	[thread overview]
Message-ID: <3573c0dd-baa8-5313-067a-eec6b04f0f36@tessares.net> (raw)
In-Reply-To: <20200603181455.4sajgdyat7rkxxnf@ast-mbp.dhcp.thefacebook.com>

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@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.

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@tessares.net
Tessares SA | Hybrid Access Solutions
www.tessares.net
1 Avenue Jean Monnet, 1348 Louvain-la-Neuve, Belgium