bpf: Sample BPF program to set congestion control

always += tcp_synrto_kern.o

always += tcp_rwnd_kern.o

always += tcp_bufs_kern.o

always += tcp_cong_kern.o

HOSTCFLAGS += -I$(objtree)/usr/include

HOSTCFLAGS += -I$(srctree)/tools/lib/

/* 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 deteremined by IPv6 prefix).

 *

 * Use load_sock_ops 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_helpers.h"

#include "bpf_endian.h"

#define DEBUG 1

#define bpf_printk(fmt, ...)					\

({								\

	       char ____fmt[] = fmt;				\

	       bpf_trace_printk(____fmt, sizeof(____fmt),	\

				##__VA_ARGS__);			\

})

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)

		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";