On 2/19/19, 10:30 AM, "Eric Dumazet" <eric.duma...@gmail.com> wrote:
On 02/18/2019 09:38 PM, brakmo wrote:
> This patch adds a new bpf helper BPF_FUNC_skb_set_ecn
> "int bpf_skb_set_Ecn(struct sk_buff *skb)". It is added to
> BPF_PROG_TYPE_CGROUP_SKB typed bpf_prog which currently can
> be attached to the ingress and egress path. This type of
> bpf_prog cannot modify the skb directly.
>
> This helper is used to set the ECN bits (2) of the IPv6 or IPv4
> header in skb. It can be used by a bpf_prog to manage egress
> network bandwdith limit per cgroupv2 by inducing an ECN
> response in the TCP sender (when the packet is ECN enabled).
> This works best when using DCTCP.
> +
> +BPF_CALL_2(bpf_skb_set_ecn, struct sk_buff *, skb, u32, val)
> +{
> + struct ipv6hdr *ip6h = ipv6_hdr(skb);
> +
> + if ((val & ~0x3) != 0)
> + return -EINVAL;
> +
> + if (ip6h->version == 6) {
> + ip6h->flow_lbl[0] = (ip6h->flow_lbl[0] & ~0x30) | (val << 4);
> + return 0;
> + } else if (ip6h->version == 4) {
> + struct iphdr *ip4h = (struct iphdr *)ip6h;
> +
> + ip4h->tos = (ip4h->tos & ~0x3) | val;
Why is not the IPv4 checksum recomputed here ?
If you leave this task to the caller, this should be documented.
These hard coded constants are not really nice.
Why not simply using INET_ECN_set_ce() which is IPv4/IPv6 ready ?
Do you really need to set anything else than CE ?
Good point, thank you. I will use it.
