/* Copyright (c) 2017 Facebook
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* BPF program to set initial receive window to 40 packets when using IPv6
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* and the first 5.5 bytes of the IPv6 addresses are not the same (in this
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* example that means both hosts are not the same datacenter).
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*
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* Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
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*/
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#include <uapi/linux/bpf.h>
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#include <uapi/linux/if_ether.h>
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#include <uapi/linux/if_packet.h>
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#include <uapi/linux/ip.h>
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#include <linux/socket.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_endian.h>
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#define DEBUG 1
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SEC("sockops")
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int bpf_rwnd(struct bpf_sock_ops *skops)
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{
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int rv = -1;
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int op;
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/* For testing purposes, only execute rest of BPF program
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* if neither port numberis 55601
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*/
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if (bpf_ntohl(skops->remote_port) !=
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55601 && skops->local_port != 55601) {
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skops->reply = -1;
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return 1;
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}
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op = (int) skops->op;
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#ifdef DEBUG
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bpf_printk("BPF command: %d\n", op);
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#endif
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/* Check for RWND_INIT operation and IPv6 addresses */
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if (op == BPF_SOCK_OPS_RWND_INIT &&
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skops->family == AF_INET6) {
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/* If the first 5.5 bytes of the IPv6 address are not the same
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* then both hosts are not in the same datacenter
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* so use a larger initial advertized window (40 packets)
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*/
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if (skops->local_ip6[0] != skops->remote_ip6[0] ||
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(bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) !=
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(bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000))
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rv = 40;
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}
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#ifdef DEBUG
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bpf_printk("Returning %d\n", rv);
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#endif
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skops->reply = rv;
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return 1;
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}
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char _license[] SEC("license") = "GPL";
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