netdev - Re: [bpf-next v2 8/9] bpf: Provide helper to do forwarding lookups in kernel FIB table

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Message-ID: <cc9f1289-e5d0-7ad0-c796-c91373f5c399@iogearbox.net>
Date:   Wed, 9 May 2018 23:49:47 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     David Ahern <dsahern@...il.com>, netdev@...r.kernel.org,
        borkmann@...earbox.net, ast@...nel.org
Cc:     davem@...emloft.net, shm@...ulusnetworks.com,
        roopa@...ulusnetworks.com, brouer@...hat.com, toke@...e.dk,
        john.fastabend@...il.com
Subject: Re: [bpf-next v2 8/9] bpf: Provide helper to do forwarding lookups in
 kernel FIB table

On 05/09/2018 11:39 PM, David Ahern wrote:
> On 5/9/18 3:29 PM, David Ahern wrote:
>> On 5/9/18 2:44 PM, Daniel Borkmann wrote:
>>> Generally, no objection. However, could we get rid of the two extra includes altogether
>>> to avoid running into any such dependency issue? Right now the only includes we have in
>>> the bpf uapi header is linux/types.h and linux/bpf_common.h (latter has no extra deps
>>> by itself). Both the ETH_ALEN and struct in6_addr are in uapi and therefore never allowed
>>> to change so we can e.g. avoid to use ETH_ALEN and just have the value instead. In the
>>> other places of the header we use __u32 remote_ipv6[4], __u32 src_ip6[4] etc to denote
>>> a v6 address, we could do the same here and should be all good then.
>>
>> I was able to drop the include of linux/in6.h and still use in6_addr. I
>> would prefer to keep in6_addr since it works and avoid the need to add
>> typecasts.
> 
> Never mind; that was working because if_ether.h was pulling in skbuff.h
> which included in6.h.
>
>> As for ETH_ALEN, I could redefine it but it just kicks the can down the
>> road. If if_ether.h is included after bpf.h, it will cause redefinition
>> warnings.
> 
> I guess I will continue the open coded magic numbers for mac and ipv6
> addresses.

Agree, it will avoid breakage. We cannot assume that every BPF prog out there has
one specific ordering of if_ether.h and bpf.h includes. Open coding the numbers
seems best here.