bpf: Sample bpf program to set initial window

always += test_map_in_map_kern.o

always += cookie_uid_helper_example.o

always += tcp_synrto_kern.o

always += tcp_rwnd_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 receive window to 40 packets when using IPv6

 * and the first 5.5 bytes of the IPv6 addresses are not the same (in this

 * example that means both hosts are not the same datacenter).

 *

 * 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_rwnd(struct bpf_sock_ops *skops)

{

	int rv = -1;

	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 for RWND_INIT operation and IPv6 addresses */

	if (op == BPF_SOCK_OPS_RWND_INIT &&

		skops->family == AF_INET6) {

		/* If the first 5.5 bytes of the IPv6 address are not the same

		 * then both hosts are not in the same datacenter

		 * so use a larger initial advertized window (40 packets)

		 */

		if (skops->local_ip6[0] != skops->remote_ip6[0] ||

		    (bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) !=

		    (bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000))

			rv = 40;

	}

#ifdef DEBUG

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

#endif

	skops->reply = rv;

	return 1;

}

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