// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2020, Tessares SA. */
/* Copyright (c) 2024, Kylin Software */

/* vmlinux.h, bpf_helpers.h and other 'define' */
#include "bpf_tracing_net.h"
#include "mptcp_bpf.h"

char _license[] SEC("license") = "GPL";

char cc[TCP_CA_NAME_MAX] = "reno";
int pid;

/* Associate a subflow counter to each token */
struct {
        __uint(type, BPF_MAP_TYPE_HASH);
        __uint(key_size, sizeof(__u32));
        __uint(value_size, sizeof(__u32));
        __uint(max_entries, 100);
} mptcp_sf SEC(".maps");

SEC("sockops")
int mptcp_subflow(struct bpf_sock_ops *skops)
{
        __u32 init = 1, key, mark, *cnt;
        struct mptcp_sock *msk;
        struct bpf_sock *sk;
        int err;

        if (skops->op != BPF_SOCK_OPS_TCP_CONNECT_CB)
                return 1;

        sk = skops->sk;
        if (!sk)
                return 1;

        msk = bpf_skc_to_mptcp_sock(sk);
        if (!msk)
                return 1;

        key = msk->token;
        cnt = bpf_map_lookup_elem(&mptcp_sf, &key);
        if (cnt) {
                /* A new subflow is added to an existing MPTCP connection */
                __sync_fetch_and_add(cnt, 1);
                mark = *cnt;
        } else {
                /* A new MPTCP connection is just initiated and this is its primary subflow */
                bpf_map_update_elem(&mptcp_sf, &key, &init, BPF_ANY);
                mark = init;
        }

        /* Set the mark of the subflow's socket based on appearance order */
        err = bpf_setsockopt(skops, SOL_SOCKET, SO_MARK, &mark, sizeof(mark));
        if (err < 0)
                return 1;
        if (mark == 2)
                err = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION, cc, TCP_CA_NAME_MAX);

        return 1;
}

static int _check_getsockopt_subflow_mark(struct mptcp_sock *msk, struct bpf_sockopt *ctx)
{
        struct mptcp_subflow_context *subflow;
        int i = 0;

        mptcp_for_each_subflow(msk, subflow) {
                struct sock *ssk;

                ssk = mptcp_subflow_tcp_sock(bpf_core_cast(subflow,
                                                           struct mptcp_subflow_context));

                if (ssk->sk_mark != ++i) {
                        ctx->retval = -2;
                        break;
                }
        }

        return 1;
}

static int _check_getsockopt_subflow_cc(struct mptcp_sock *msk, struct bpf_sockopt *ctx)
{
        struct mptcp_subflow_context *subflow;

        mptcp_for_each_subflow(msk, subflow) {
                struct inet_connection_sock *icsk;
                struct sock *ssk;

                ssk = mptcp_subflow_tcp_sock(bpf_core_cast(subflow,
                                                           struct mptcp_subflow_context));
                icsk = bpf_core_cast(ssk, struct inet_connection_sock);

                if (ssk->sk_mark == 2 &&
                    __builtin_memcmp(icsk->icsk_ca_ops->name, cc, TCP_CA_NAME_MAX)) {
                        ctx->retval = -2;
                        break;
                }
        }

        return 1;
}

SEC("cgroup/getsockopt")
int _getsockopt_subflow(struct bpf_sockopt *ctx)
{
        struct bpf_sock *sk = ctx->sk;
        struct mptcp_sock *msk;

        if (bpf_get_current_pid_tgid() >> 32 != pid)
                return 1;

        if (!sk || sk->protocol != IPPROTO_MPTCP ||
            (!(ctx->level == SOL_SOCKET && ctx->optname == SO_MARK) &&
             !(ctx->level == SOL_TCP && ctx->optname == TCP_CONGESTION)))
                return 1;

        msk = bpf_core_cast(sk, struct mptcp_sock);
        if (msk->pm.extra_subflows != 1) {
                ctx->retval = -1;
                return 1;
        }

        if (ctx->optname == SO_MARK)
                return _check_getsockopt_subflow_mark(msk, ctx);
        return _check_getsockopt_subflow_cc(msk, ctx);
}