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

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Message-ID: <2F824DC2-E349-40E5-9894-5840D866674F@fb.com>
Date:   Wed, 24 Jan 2018 21:14:49 +0000
From:   Lawrence Brakmo <brakmo@...com>
To:     Yuchung Cheng <ycheng@...gle.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 1/24/18, 12:02 PM, "netdev-owner@...r.kernel.org on behalf of Yuchung Cheng" <netdev-owner@...r.kernel.org on behalf of ycheng@...gle.com> wrote:

    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.
    
Good point, thanks Yuchung. I will do a new patch shortly that will also pass the err value to the BPF program.

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