[PATCH net-next v4 04/16] bpf: Sample bpf program to set SYN/SYN-ACK RTOs

[Lawrence Brakmo <brakmo@fb.com>]

The sample BPF program, tcp_synrto_kern.c, sets the SYN and SYN-ACK
RTOs to 10ms when both hosts are within the same datacenter (i.e.
small RTTs) in an environment where common IPv6 prefixes indicate
both hosts are in the same data center.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
---
 samples/bpf/Makefile          |  1 +
 samples/bpf/tcp_synrto_kern.c | 60 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 samples/bpf/tcp_synrto_kern.c

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 015589b..e29370a 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -113,6 +113,7 @@ always += lwt_len_hist_kern.o
 always += xdp_tx_iptunnel_kern.o
 always += test_map_in_map_kern.o
 always += cookie_uid_helper_example.o
+always += tcp_synrto_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
diff --git a/samples/bpf/tcp_synrto_kern.c b/samples/bpf/tcp_synrto_kern.c
new file mode 100644
index 0000000..b16ac39
--- /dev/null
+++ b/samples/bpf/tcp_synrto_kern.c
@@ -0,0 +1,60 @@
+/* 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 SYN and SYN-ACK RTOs to 10ms when using IPv6 addresses
+ * and the first 5.5 bytes of the IPv6 addresses are the same (in this example
+ * that means both hosts are in the same datacenter.
+ */
+
+#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"
+
+#define DEBUG 1
+
+SEC("sockops")
+int bpf_synrto(struct bpf_sock_ops *skops)
+{
+	char fmt1[] = "BPF command: %d\n";
+	char fmt2[] = "  Returning %d\n";
+	int rv = -1;
+	int op;
+
+	/* For testing purposes, only execute rest of BPF program
+	 * if neither port numberis 55601
+	 */
+	if (skops->remote_port != 55601 && skops->local_port != 55601)
+		return -1;
+
+	op = (int) skops->op;
+
+#ifdef DEBUG
+	bpf_trace_printk(fmt1, sizeof(fmt1), op);
+#endif
+
+	/* Check for TIMEOUT_INIT operation and IPv6 addresses */
+	if (op == BPF_SOCK_OPS_TIMEOUT_INIT &&
+		skops->family == AF_INET6) {
+
+		/* If the first 5.5 bytes of the IPv6 address are the same
+		 * then both hosts are in the same datacenter
+		 * so use an RTO of 10ms
+		 */
+		if (skops->local_ip6[0] == skops->remote_ip6[0] &&
+		    (skops->local_ip6[1] & 0xfff00000) ==
+		    (skops->remote_ip6[1] & 0xfff00000))
+			rv = 10;
+	}
+#ifdef DEBUG
+	bpf_trace_printk(fmt2, sizeof(fmt2), rv);
+#endif
+	skops->reply = rv;
+	return 1;
+}
+char _license[] SEC("license") = "GPL";
-- 
2.9.3