// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2021 Facebook */
#include "bpf_tracing_net.h"

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

__s32 page_size = 0;

const char cc_reno[TCP_CA_NAME_MAX] = "reno";
const char cc_cubic[TCP_CA_NAME_MAX] = "cubic";

SEC("cgroup/setsockopt")
int sockopt_qos_to_cc(struct bpf_sockopt *ctx)
{
        void *optval_end = ctx->optval_end;
        int *optval = ctx->optval;
        char buf[TCP_CA_NAME_MAX];

        if (ctx->level != SOL_IPV6 || ctx->optname != IPV6_TCLASS)
                goto out;

        if (optval + 1 > optval_end)
                return 0; /* EPERM, bounds check */

        if (bpf_getsockopt(ctx->sk, SOL_TCP, TCP_CONGESTION, &buf, sizeof(buf)))
                return 0;

        if (bpf_strncmp(buf, sizeof(buf), cc_cubic))
                return 0;

        if (*optval == 0x2d) {
                if (bpf_setsockopt(ctx->sk, SOL_TCP, TCP_CONGESTION, (void *)&cc_reno,
                                sizeof(cc_reno)))
                        return 0;
        }
        return 1;

out:
        /* optval larger than PAGE_SIZE use kernel's buffer. */
        if (ctx->optlen > page_size)
                ctx->optlen = 0;
        return 1;
}