Subject: Re: [PATCH net-next v2 3/5] bpf: BPF for lightweight tunnel encapsulation

From: Roopa Prabhu <[email-masked]>
Date: Wed, 02 Nov 2016 06:39:13 -0700

On 10/31/16, 5:37 PM, Thomas Graf wrote:
> Register two new BPF prog types BPF_PROG_TYPE_LWT_IN and
> BPF_PROG_TYPE_LWT_OUT which are invoked if a route contains a
> LWT redirection of type LWTUNNEL_ENCAP_BPF.
>
> The separate program types are required because manipulation of
> packet data is only allowed on the output and transmit path as
> the subsequent dst_input() call path assumes an IP header
> validated by ip_rcv(). The BPF programs will be handed an skb
> with the L3 header attached and may return one of the following
> return codes:
>
>  BPF_OK - Continue routing as per nexthop
>  BPF_DROP - Drop skb and return EPERM
>  BPF_REDIRECT - Redirect skb to device as per redirect() helper.
>                 (Only valid on lwtunnel_xmit() hook)
>
> The return codes are binary compatible with their TC_ACT_
> relatives to ease compatibility.
>
> A new helper bpf_skb_push() is added which allows to preprend an
> L2 header in front of the skb, extend the existing L3 header, or
> both. This allows to address a wide range of issues:
>  - Optimize L2 header construction when L2 information is always
>    static to avoid ARP/NDisc lookup.
>  - Extend IP header to add additional IP options.
>  - Perform simple encapsulation where offload is of no concern.
>    (The existing funtionality to attach a tunnel key to the skb
>     and redirect to a tunnel net_device to allow for offload
>     continues to work obviously).
>
> Signed-off-by: Thomas Graf <[email-masked]>
> ---
>  
[snip]
> diff --git a/net/Kconfig b/net/Kconfig
> index 7b6cd34..7554f12 100644
> --- a/net/Kconfig
> +++ b/net/Kconfig
> @@ -396,6 +396,7 @@ source "net/nfc/Kconfig"
>  
>  config LWTUNNEL
>  	bool "Network light weight tunnels"
> +	depends on IPV6 || IPV6=n
>  	---help---
>  	  This feature provides an infrastructure to support light weight
>  	  tunnels like mpls. There is no netdevice associated with a light
> diff --git a/net/core/Makefile b/net/core/Makefile
> index d6508c2..a675fd3 100644
> --- a/net/core/Makefile
> +++ b/net/core/Makefile
> @@ -23,7 +23,7 @@ obj-$(CONFIG_NETWORK_PHY_TIMESTAMPING) += timestamping.o
>  obj-$(CONFIG_NET_PTP_CLASSIFY) += ptp_classifier.o
>  obj-$(CONFIG_CGROUP_NET_PRIO) += netprio_cgroup.o
>  obj-$(CONFIG_CGROUP_NET_CLASSID) += netclassid_cgroup.o
> -obj-$(CONFIG_LWTUNNEL) += lwtunnel.o
> +obj-$(CONFIG_LWTUNNEL) += lwtunnel.o lwt_bpf.o

Any reason you want to keep lwt bpf under the main CONFIG_LWTUNNEL infra config ?.
since it is defined as yet another plug-gable encap function, seems like it will be better under a separate
CONFIG_LWTUNNEL_BPF or CONFIG_LWT_BPF that depends on CONFIG_LWTUNNEL