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/* 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 initial receive window to 40 packets when using IPv6
* and the first 5.5 bytes of the IPv6 addresses are not the same (in this
* example that means both hosts are not the same datacenter).
*
* Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
*/
#include <uapi/linux/bpf.h>
#include <uapi/linux/if_ether.h>
#include <uapi/linux/if_packet.h>
#include <uapi/linux/ip.h>
#include <linux/socket.h>
#include "bpf_helpers.h"
#include "bpf_endian.h"
#define DEBUG 1
SEC("sockops")
int bpf_rwnd(struct bpf_sock_ops *skops)
{
int rv = -1;
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 for RWND_INIT operation and IPv6 addresses */
if (op == BPF_SOCK_OPS_RWND_INIT &&
skops->family == AF_INET6) {
/* If the first 5.5 bytes of the IPv6 address are not the same
* then both hosts are not in the same datacenter
* so use a larger initial advertized window (40 packets)
*/
if (skops->local_ip6[0] != skops->remote_ip6[0] ||
(bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) !=
(bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000))
rv = 40;
}
#ifdef DEBUG
bpf_printk("Returning %d\n", rv);
#endif
skops->reply = rv;
return 1;
}
char _license[] SEC("license") = "GPL";
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