netdev - Re: [PATCH bpf-next 1/9] bpf: Add bpf helper bpf_tcp_enter

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Date:   Thu, 21 Feb 2019 03:18:35 +0000
From:   Lawrence Brakmo <brakmo@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>
CC:     Martin Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        "Daniel Borkmann" <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 1/9] bpf: Add bpf helper bpf_tcp_enter_cwr

On 2/19/19, 10:30 AM, "Eric Dumazet" <eric.dumazet@...il.com> wrote:

    
    
    On 02/18/2019 09:38 PM, brakmo wrote:
    > This patch adds a new bpf helper BPF_FUNC_tcp_enter_cwr
    > "int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)".
    > It is added to BPF_PROG_TYPE_CGROUP_SKB typed bpf_prog
    > which currently can be attached to the ingress and egress
    > path.
    >
    
    Do we have the guarantee socket is a tcp one, and that the caller
    owns the socket lock ?

Yes. The BPF verifier insures that a pointer to bpf_tcp_sock points to a non-NULL full tcp socket.

    
    Please describe the exact context for this helper being used.

>From cgroup skb egress bpf program. When the BPF program determines that a flow needs to slow down, it will call bpf_tcp_enter_cwr(tp).