bpf: Sample BPF program to set initial cwnd

always += tcp_rwnd_kern.o

always += tcp_bufs_kern.o

always += tcp_cong_kern.o

always += tcp_iw_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 initial congestion window and initial receive

 * window to 40 packets and send and receive buffers to 1.5MB. This

 * would usually be done after doing appropriate checks that indicate

 * the hosts are far enough away (i.e. large RTT).

 *

 * Use load_sock_ops 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

#define bpf_printk(fmt, ...)					\

({								\

	       char ____fmt[] = fmt;				\

	       bpf_trace_printk(____fmt, sizeof(____fmt),	\

				##__VA_ARGS__);			\

})

SEC("sockops")

int bpf_iw(struct bpf_sock_ops *skops)

{

	int bufsize = 1500000;

	int rwnd_init = 40;

	int iw = 40;

	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

	/* Usually there would be a check to insure the hosts are far

	 * from each other so it makes sense to increase buffer sizes

	 */

	switch (op) {

	case BPF_SOCK_OPS_RWND_INIT:

		rv = rwnd_init;

		break;

	case BPF_SOCK_OPS_TCP_CONNECT_CB:

		/* Set sndbuf and rcvbuf of active connections */

		rv = bpf_setsockopt(skops, SOL_SOCKET, SO_SNDBUF, &bufsize,

				    sizeof(bufsize));

		rv = rv*100 + bpf_setsockopt(skops, SOL_SOCKET, SO_RCVBUF,

					     &bufsize, sizeof(bufsize));

		break;

	case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:

		rv = bpf_setsockopt(skops, SOL_TCP, TCP_BPF_IW, &iw,

				    sizeof(iw));

		break;

	case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:

		/* Set sndbuf and rcvbuf of passive connections */

		rv = bpf_setsockopt(skops, SOL_SOCKET, SO_SNDBUF, &bufsize,

				    sizeof(bufsize));

		rv = rv*100 + bpf_setsockopt(skops, SOL_SOCKET, SO_RCVBUF,

					     &bufsize, sizeof(bufsize));

		break;

	default:

		rv = -1;

	}

#ifdef DEBUG

	bpf_printk("Returning %d\n", rv);

#endif

	skops->reply = rv;

	return 1;

}

char _license[] SEC("license") = "GPL";