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

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Date:   Wed, 9 May 2018 14:49:42 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        borkmann@...earbox.net, ast@...nel.org, 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 Wed, May 09, 2018 at 03:39:52PM -0600, 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.

That's the only way.
Adding
+#include <linux/if_ether.h>
+#include <linux/in6.h>
to uapi/bpf.h is no-go. It will cause all sorts of breakage
not only to kernel build as we realized, but to various user space apps too.
Please use be32 ipv6[4] and hard coded mac instead.