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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 base_rtt to 80us when host is running TCP-NV and
* 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_basertt(struct bpf_sock_ops *skops)
{
char cong[20];
char nv[] = "nv";
int rv = 0, n;
int op;
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_BASE_RTT:
n = bpf_getsockopt(skops, SOL_TCP, TCP_CONGESTION,
cong, sizeof(cong));
if (!n && !__builtin_memcmp(cong, nv, sizeof(nv))) {
/* Set base_rtt to 80us */
rv = 80;
} else if (n) {
rv = n;
} else {
rv = -1;
}
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";
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