/* 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 base_rtt to 80us when host is running TCP-NV and
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* both hosts are in the same datacenter (as determined by IPv6 prefix).
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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/tcp.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_basertt(struct bpf_sock_ops *skops)
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{
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char cong[20];
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char nv[] = "nv";
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int rv = 0, n;
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int op;
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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 if both hosts are in the same datacenter. For this
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* example they are if the 1st 5.5 bytes in the IPv6 address
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* are the same.
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*/
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if (skops->family == AF_INET6 &&
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skops->local_ip6[0] == skops->remote_ip6[0] &&
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(bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
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(bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
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switch (op) {
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case BPF_SOCK_OPS_BASE_RTT:
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n = bpf_getsockopt(skops, SOL_TCP, TCP_CONGESTION,
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cong, sizeof(cong));
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if (!n && !__builtin_memcmp(cong, nv, sizeof(nv)+1)) {
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/* Set base_rtt to 80us */
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rv = 80;
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} else if (n) {
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rv = n;
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} else {
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rv = -1;
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}
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break;
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default:
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rv = -1;
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}
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} else {
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rv = -1;
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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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