netdev - Re: [PATCH/v4] bpf: add bpf_skb_adjust_room flag BPF_F_ADJ_ROOM_ENCAP_L2

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Date:   Wed, 3 Mar 2021 22:40:22 -0500
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Xuesen Huang <hxseverything@...il.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>, bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Zhiyong Cheng <chengzhiyong@...ishou.com>,
        Li Wang <wangli09@...ishou.com>
Subject: Re: [PATCH/v4] bpf: add bpf_skb_adjust_room flag BPF_F_ADJ_ROOM_ENCAP_L2_ETH

> > Instead of untyped macros, I'd define encap_ipv4 as a function that
> > calls __encap_ipv4.
> >
> > And no need for encap_ipv4_with_ext_proto equivalent to __encap_ipv4.
> >
> I defined these macros to try to keep the existing  invocation for encap_ipv4/6
> as the same, if we define this as a function all invocation should be modified?

You can leave the existing invocations the same and make the new
callers caller __encap_ipv4 directly, which takes one extra argument?
Adding a __ prefixed variant with extra args is a common pattern.

> >>        /* add L2 encap (if specified) */
> >> +       l2_hdr = (__u8 *)&h_outer + olen;
> >>        switch (l2_proto) {
> >>        case ETH_P_MPLS_UC:
> >> -               *((__u32 *)((__u8 *)&h_outer + olen)) = mpls_label;
> >> +               *(__u32 *)l2_hdr = mpls_label;
> >>                break;
> >>        case ETH_P_TEB:
> >> -               if (bpf_skb_load_bytes(skb, 0, (__u8 *)&h_outer + olen,
> >> -                                      ETH_HLEN))
> >
> > This is non-standard indentation? Here and elsewhere.
> I thinks it’s a previous issue.

Ah right. Bad example. How about in __encap_vxlan_eth

+               return encap_ipv4_with_ext_proto(skb, IPPROTO_UDP,
+                               ETH_P_TEB, EXTPROTO_VXLAN);

> >> @@ -278,13 +321,24 @@ static __always_inline int encap_ipv6(struct __sk_buff *skb, __u8 encap_proto,
> >>        }
> >>
> >>        /* add L2 encap (if specified) */
> >> +       l2_hdr = (__u8 *)&h_outer + olen;
> >>        switch (l2_proto) {
> >>        case ETH_P_MPLS_UC:
> >> -               *((__u32 *)((__u8 *)&h_outer + olen)) = mpls_label;
> >> +               *(__u32 *)l2_hdr = mpls_label;
> >>                break;
> >>        case ETH_P_TEB:
> >> -               if (bpf_skb_load_bytes(skb, 0, (__u8 *)&h_outer + olen,
> >> -                                      ETH_HLEN))
> >> +               flags |= BPF_F_ADJ_ROOM_ENCAP_L2_ETH;
> >
> > This is a change also for the existing case. Correctly so, I imagine.
> > But the test used to pass with the wrong protocol?
> Yes all tests pass. I’m not sure should we add this flag for the existing tests
> which encap eth as the l2 header or only for the Vxlan test?

It is correct in both cases. If it does not break anything, I would do both.

Thanks,

  Willem