xref: /openbmc/linux/samples/bpf/tcp_cong_kern.c (revision 7cf245a3)
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 congestion control to dctcp when both hosts are
8  * in the same datacenter (as deteremined by IPv6 prefix).
9  *
10  * Use "bpftool cgroup attach $cg sock_ops $prog" to load this BPF program.
11  */
12 
13 #include <uapi/linux/bpf.h>
14 #include <uapi/linux/tcp.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_cong(struct bpf_sock_ops * skops)25 int bpf_cong(struct bpf_sock_ops *skops)
26 {
27 	char cong[] = "dctcp";
28 	int rv = 0;
29 	int op;
30 
31 	/* For testing purposes, only execute rest of BPF program
32 	 * if neither port numberis 55601
33 	 */
34 	if (bpf_ntohl(skops->remote_port) != 55601 &&
35 	    skops->local_port != 55601) {
36 		skops->reply = -1;
37 		return 1;
38 	}
39 
40 	op = (int) skops->op;
41 
42 #ifdef DEBUG
43 	bpf_printk("BPF command: %d\n", op);
44 #endif
45 
46 	/* Check if both hosts are in the same datacenter. For this
47 	 * example they are if the 1st 5.5 bytes in the IPv6 address
48 	 * are the same.
49 	 */
50 	if (skops->family == AF_INET6 &&
51 	    skops->local_ip6[0] == skops->remote_ip6[0] &&
52 	    (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
53 	    (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
54 		switch (op) {
55 		case BPF_SOCK_OPS_NEEDS_ECN:
56 			rv = 1;
57 			break;
58 		case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
59 			rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
60 					    cong, sizeof(cong));
61 			break;
62 		case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
63 			rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
64 					    cong, sizeof(cong));
65 			break;
66 		default:
67 			rv = -1;
68 		}
69 	} else {
70 		rv = -1;
71 	}
72 #ifdef DEBUG
73 	bpf_printk("Returning %d\n", rv);
74 #endif
75 	skops->reply = rv;
76 	return 1;
77 }
78 char _license[] SEC("license") = "GPL";
79