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

From: Maciej Fijalkowski <[email-masked]>
Date: Fri, 31 Jul 2020 13:52:25 +0200

On Fri, Jul 31, 2020 at 01:44:19PM +0900, Yoshiki Komachi wrote:
> This patch adds a new bpf helper to access FDB in the kernel tables
> from XDP programs. The helper enables us to find the destination port
> of master bridge in XDP layer with high speed. If an entry in the
> tables is successfully found, egress device index will be returned.
> 
> In cases of failure, packets will be dropped or forwarded to upper
> networking stack in the kernel by XDP programs. Multicast and broadcast
> packets are currently not supported. Thus, these will need to be
> passed to upper layer on the basis of XDP_PASS action.
> 
> The API uses destination MAC and VLAN ID as keys, so XDP programs
> need to extract these from forwarded packets.
> 
> Signed-off-by: Yoshiki Komachi <[email-masked]>
> ---
>  include/uapi/linux/bpf.h       | 28 +++++++++++++++++++++
>  net/core/filter.c              | 45 ++++++++++++++++++++++++++++++++++
>  scripts/bpf_helpers_doc.py     |  1 +
>  tools/include/uapi/linux/bpf.h | 28 +++++++++++++++++++++
>  4 files changed, 102 insertions(+)
> 

[...]

> 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
> @@ -45,6 +45,7 @@
>  #include <linux/filter.h>
>  #include <linux/ratelimit.h>
>  #include <linux/seccomp.h>
> +#include <linux/if_bridge.h>
>  #include <linux/if_vlan.h>
>  #include <linux/bpf.h>
>  #include <linux/btf.h>
> @@ -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;
> +
> +	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;

small nit: you could move that validation before dev_net() call.

> +
> +	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);
> +	if (dst) {
> +		params->ifindex = dst->ifindex;
> +		return BPF_FDB_LKUP_RET_SUCCESS;
> +	}
> +
> +	return BPF_FDB_LKUP_RET_NOENT;
> +}