xref: /linux/samples/bpf/tcp_clamp_kern.c (revision 37744feebc086908fd89760650f458ab19071750)
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  * Sample BPF program to set send and receive buffers to 150KB, sndcwnd clamp
8  * to 100 packets and SYN and SYN_ACK RTOs to 10ms when both hosts are within
9  * the same datacenter. For his example, we assume they are within the same
10  * datacenter when the first 5.5 bytes of their IPv6 addresses are the same.
11  *
12  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
13  */
14 
15 #include <uapi/linux/bpf.h>
16 #include <uapi/linux/if_ether.h>
17 #include <uapi/linux/if_packet.h>
18 #include <uapi/linux/ip.h>
19 #include <linux/socket.h>
20 #include <bpf/bpf_helpers.h>
21 #include <bpf/bpf_endian.h>
22 
23 #define DEBUG 1
24 
25 SEC("sockops")
26 int bpf_clamp(struct bpf_sock_ops *skops)
27 {
28 	int bufsize = 150000;
29 	int to_init = 10;
30 	int clamp = 100;
31 	int rv = 0;
32 	int op;
33 
34 	/* For testing purposes, only execute rest of BPF program
35 	 * if neither port numberis 55601
36 	 */
37 	if (bpf_ntohl(skops->remote_port) != 55601 && skops->local_port != 55601) {
38 		skops->reply = -1;
39 		return 0;
40 	}
41 
42 	op = (int) skops->op;
43 
44 #ifdef DEBUG
45 	bpf_printk("BPF command: %d\n", op);
46 #endif
47 
48 	/* Check that both hosts are within same datacenter. For this example
49 	 * it is the case when the first 5.5 bytes of their IPv6 addresses are
50 	 * the same.
51 	 */
52 	if (skops->family == AF_INET6 &&
53 	    skops->local_ip6[0] == skops->remote_ip6[0] &&
54 	    (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
55 	    (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
56 		switch (op) {
57 		case BPF_SOCK_OPS_TIMEOUT_INIT:
58 			rv = to_init;
59 			break;
60 		case BPF_SOCK_OPS_TCP_CONNECT_CB:
61 			/* Set sndbuf and rcvbuf of active connections */
62 			rv = bpf_setsockopt(skops, SOL_SOCKET, SO_SNDBUF,
63 					    &bufsize, sizeof(bufsize));
64 			rv += bpf_setsockopt(skops, SOL_SOCKET,
65 					     SO_RCVBUF, &bufsize,
66 					     sizeof(bufsize));
67 			break;
68 		case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
69 			rv = bpf_setsockopt(skops, SOL_TCP,
70 					    TCP_BPF_SNDCWND_CLAMP,
71 					    &clamp, sizeof(clamp));
72 			break;
73 		case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
74 			/* Set sndbuf and rcvbuf of passive connections */
75 			rv = bpf_setsockopt(skops, SOL_TCP,
76 					    TCP_BPF_SNDCWND_CLAMP,
77 					    &clamp, sizeof(clamp));
78 			rv += bpf_setsockopt(skops, SOL_SOCKET,
79 					     SO_SNDBUF, &bufsize,
80 					     sizeof(bufsize));
81 			rv += bpf_setsockopt(skops, SOL_SOCKET,
82 					     SO_RCVBUF, &bufsize,
83 					     sizeof(bufsize));
84 			break;
85 		default:
86 			rv = -1;
87 		}
88 	} else {
89 		rv = -1;
90 	}
91 #ifdef DEBUG
92 	bpf_printk("Returning %d\n", rv);
93 #endif
94 	skops->reply = rv;
95 	return 1;
96 }
97 char _license[] SEC("license") = "GPL";
98