/* Copyright (c) 2017 Facebook
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 *
 * BPF program to set congestion control to dctcp when both hosts are
 * in the same datacenter (as determined by IPv6 prefix).
 *
 * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
 */

#include <uapi/linux/bpf.h>
#include <uapi/linux/tcp.h>
#include <uapi/linux/if_ether.h>
#include <uapi/linux/if_packet.h>
#include <uapi/linux/ip.h>
#include <linux/socket.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_endian.h>

#define DEBUG 1

SEC("sockops")
int bpf_cong(struct bpf_sock_ops *skops)
{
        char cong[] = "dctcp";
        int rv = 0;
        int op;

        /* For testing purposes, only execute rest of BPF program
         * if neither port numberis 55601
         */
        if (bpf_ntohl(skops->remote_port) != 55601 &&
            skops->local_port != 55601) {
                skops->reply = -1;
                return 1;
        }

        op = (int) skops->op;

#ifdef DEBUG
        bpf_printk("BPF command: %d\n", op);
#endif

        /* Check if both hosts are in the same datacenter. For this
         * example they are if the 1st 5.5 bytes in the IPv6 address
         * are the same.
         */
        if (skops->family == AF_INET6 &&
            skops->local_ip6[0] == skops->remote_ip6[0] &&
            (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
            (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
                switch (op) {
                case BPF_SOCK_OPS_NEEDS_ECN:
                        rv = 1;
                        break;
                case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
                        rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
                                            cong, sizeof(cong));
                        break;
                case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
                        rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
                                            cong, sizeof(cong));
                        break;
                default:
                        rv = -1;
                }
        } else {
                rv = -1;
        }
#ifdef DEBUG
        bpf_printk("Returning %d\n", rv);
#endif
        skops->reply = rv;
        return 1;
}
char _license[] SEC("license") = "GPL";