xref: /linux/samples/bpf/tcp_rwnd_kern.c (revision 8dd06ef34b6e2f41b29fbf5fc1663780f2524285)
1 /* Copyright (c) 2017 Facebook
2  *
3  * This program is free software; you can redistribute it and/or
4  * modify it under the terms of version 2 of the GNU General Public
5  * License as published by the Free Software Foundation.
6  *
7  * BPF program to set initial receive window to 40 packets when using IPv6
8  * and the first 5.5 bytes of the IPv6 addresses are not the same (in this
9  * example that means both hosts are not the same datacenter).
10  *
11  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
12  */
13 
14 #include <uapi/linux/bpf.h>
15 #include <uapi/linux/if_ether.h>
16 #include <uapi/linux/if_packet.h>
17 #include <uapi/linux/ip.h>
18 #include <linux/socket.h>
19 #include <bpf/bpf_helpers.h>
20 #include <bpf/bpf_endian.h>
21 
22 #define DEBUG 1
23 
24 SEC("sockops")
bpf_rwnd(struct bpf_sock_ops * skops)25 int bpf_rwnd(struct bpf_sock_ops *skops)
26 {
27 	int rv = -1;
28 	int op;
29 
30 	/* For testing purposes, only execute rest of BPF program
31 	 * if neither port numberis 55601
32 	 */
33 	if (bpf_ntohl(skops->remote_port) !=
34 	    55601 && skops->local_port != 55601) {
35 		skops->reply = -1;
36 		return 1;
37 	}
38 
39 	op = (int) skops->op;
40 
41 #ifdef DEBUG
42 	bpf_printk("BPF command: %d\n", op);
43 #endif
44 
45 	/* Check for RWND_INIT operation and IPv6 addresses */
46 	if (op == BPF_SOCK_OPS_RWND_INIT &&
47 		skops->family == AF_INET6) {
48 
49 		/* If the first 5.5 bytes of the IPv6 address are not the same
50 		 * then both hosts are not in the same datacenter
51 		 * so use a larger initial advertized window (40 packets)
52 		 */
53 		if (skops->local_ip6[0] != skops->remote_ip6[0] ||
54 		    (bpf_ntohl(skops->local_ip6[1]) & 0xfffff000) !=
55 		    (bpf_ntohl(skops->remote_ip6[1]) & 0xfffff000))
56 			rv = 40;
57 	}
58 #ifdef DEBUG
59 	bpf_printk("Returning %d\n", rv);
60 #endif
61 	skops->reply = rv;
62 	return 1;
63 }
64 char _license[] SEC("license") = "GPL";
65