netdev - Re: [PATCH bpf-next v4 3/6] bpf: add redirect

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Message-ID: <34c873d1-5014-9fd4-8372-4980f6787904@gmail.com>
Date:   Wed, 30 Sep 2020 09:08:34 -0700
From:   David Ahern <dsahern@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>, ast@...nel.org
Cc:     john.fastabend@...il.com, kafai@...com, netdev@...r.kernel.org,
        bpf@...r.kernel.org, David Ahern <dsahern@...nel.org>
Subject: Re: [PATCH bpf-next v4 3/6] bpf: add redirect_neigh helper as
 redirect drop-in

On 9/30/20 8:18 AM, Daniel Borkmann wrote:
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 6116a7f54c8f..1f17c6752deb 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3652,6 +3652,19 @@ union bpf_attr {
>   * 		associated socket instead of the current process.
>   * 	Return
>   * 		The id is returned or 0 in case the id could not be retrieved.
> + *
> + * long bpf_redirect_neigh(u32 ifindex, u64 flags)
> + * 	Description
> + * 		Redirect the packet to another net device of index *ifindex*
> + * 		and fill in L2 addresses from neighboring subsystem. This helper

It is worth mentioning in the documentation that this helper does a FIB
lookup based on the skb's networking header to get the address of the
next hop and then relies on the neighbor lookup for the L2 address of
the nexthop.

> + * 		is somewhat similar to **bpf_redirect**\ (), except that it
> + * 		fills in e.g. MAC addresses based on the L3 information from
> + * 		the packet. This helper is supported for IPv4 and IPv6 protocols.
> + * 		The *flags* argument is reserved and must be 0. The helper is
> + * 		currently only supported for tc BPF program types.
> + * 	Return
> + * 		The helper returns **TC_ACT_REDIRECT** on success or
> + * 		**TC_ACT_SHOT** on error.
>   */
>  #define __BPF_FUNC_MAPPER(FN)		\
>  	FN(unspec),			\

Code change looks fine to me:

Reviewed-by: David Ahern <dsahern@...il.com>