netdev - Re: [PATCH bpf-next v8 10/12] bpf: Add BPF_SOCK_OPS_RETRANS

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Message-ID: <CAK6E8=cf2n1LHuV7uF71iBBjo6+igGe8H+OcDZc=_oqJhORLaA@mail.gmail.com>
Date:   Wed, 24 Jan 2018 12:01:41 -0800
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Lawrence Brakmo <brakmo@...com>
Cc:     netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
        Blake Matheny <bmatheny@...com>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH bpf-next v8 10/12] bpf: Add BPF_SOCK_OPS_RETRANS_CB

On Tue, Jan 23, 2018 at 11:58 PM, Lawrence Brakmo <brakmo@...com> wrote:
> Adds support for calling sock_ops BPF program when there is a
> retransmission. Two arguments are used; one for the sequence number and
> other for the number of segments retransmitted. Does not include syn-ack
> retransmissions.
>
> New op: BPF_SOCK_OPS_RETRANS_CB.
>
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
> ---
>  include/uapi/linux/bpf.h | 4 ++++
>  include/uapi/linux/tcp.h | 3 ++-
>  net/ipv4/tcp_output.c    | 3 +++
>  3 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 6998032..eb26cdb 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1039,6 +1039,10 @@ enum {
>                                          * Arg2: value of icsk_rto
>                                          * Arg3: whether RTO has expired
>                                          */
> +       BPF_SOCK_OPS_RETRANS_CB,        /* Called when skb is retransmitted.
> +                                        * Arg1: sequence number of 1st byte
> +                                        * Arg2: # segments
> +                                        */
>  };
>
>  #define TCP_BPF_IW             1001    /* Set TCP initial congestion window */
> diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
> index 129032ca..ec03a2b 100644
> --- a/include/uapi/linux/tcp.h
> +++ b/include/uapi/linux/tcp.h
> @@ -270,7 +270,8 @@ struct tcp_diag_md5sig {
>
>  /* Definitions for bpf_sock_ops_cb_flags */
>  #define BPF_SOCK_OPS_RTO_CB_FLAG       (1<<0)
> -#define BPF_SOCK_OPS_ALL_CB_FLAGS       0x1            /* Mask of all currently
> +#define BPF_SOCK_OPS_RETRANS_CB_FLAG   (1<<1)
> +#define BPF_SOCK_OPS_ALL_CB_FLAGS       0x3            /* Mask of all currently
>                                                          * supported cb flags
>                                                          */
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index d12f7f7..f7d34f01 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -2908,6 +2908,9 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs)
>         if (likely(!err)) {
>                 TCP_SKB_CB(skb)->sacked |= TCPCB_EVER_RETRANS;
>                 trace_tcp_retransmit_skb(sk, skb);
> +               if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RETRANS_CB_FLAG))
> +                       tcp_call_bpf_2arg(sk, BPF_SOCK_OPS_RETRANS_CB,
> +                                         TCP_SKB_CB(skb)->seq, segs);
Any reason to skip failed retransmission? I would think that's helpful as well.

>         } else if (err != -EBUSY) {
>                 NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRETRANSFAIL);
>         }
> --
> 2.9.5
>