netdev - Re: [RFC PATCH bpf-next 2/3] bpf: Add helper to do forwarding lookups in kernel FDB table

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Date:   Fri, 31 Jul 2020 11:15:19 -0600
From:   David Ahern <dsahern@...il.com>
To:     Yoshiki Komachi <komachi.yoshiki@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        David Ahern <dsahern@...nel.org>
Cc:     netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
        bpf@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next 2/3] bpf: Add helper to do forwarding lookups
 in kernel FDB table

On 7/30/20 10:44 PM, Yoshiki Komachi wrote:
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 654c346b7d91..68800d1b8cd5 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5084,6 +5085,46 @@ static const struct bpf_func_proto bpf_skb_fib_lookup_proto = {
>  	.arg4_type	= ARG_ANYTHING,
>  };
>  
> +#if IS_ENABLED(CONFIG_BRIDGE)
> +BPF_CALL_4(bpf_xdp_fdb_lookup, struct xdp_buff *, ctx,
> +	   struct bpf_fdb_lookup *, params, int, plen, u32, flags)
> +{
> +	struct net_device *src, *dst;
> +	struct net *net;
> +
> +	if (plen < sizeof(*params))
> +		return -EINVAL;

I need to look at the details more closely, but on first reading 2
things caught me eye:
1. you need to make sure flags is 0 since there are no supported flags
at the moment, and

> +
> +	net = dev_net(ctx->rxq->dev);
> +
> +	if (is_multicast_ether_addr(params->addr) ||
> +	    is_broadcast_ether_addr(params->addr))
> +		return BPF_FDB_LKUP_RET_NOENT;
> +
> +	src = dev_get_by_index_rcu(net, params->ifindex);
> +	if (unlikely(!src))
> +		return -ENODEV;
> +
> +	dst = br_fdb_find_port_xdp(src, params->addr, params->vlan_id);

2. this needs to be done via netdev ops to avoid referencing bridge code
which can be compiled as a module. I suspect the build robots will id
this part soon.