2 files changed, 84 insertions, 0 deletions

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 3b300db3d74d..6fdf32dffa92 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -116,6 +116,7 @@ always += cookie_uid_helper_example.o
 always += tcp_synrto_kern.o
 always += tcp_rwnd_kern.o
 always += tcp_bufs_kern.o
+always += tcp_cong_kern.o
 
 HOSTCFLAGS += -I$(objtree)/usr/include
 HOSTCFLAGS += -I$(srctree)/tools/lib/
diff --git a/samples/bpf/tcp_cong_kern.c b/samples/bpf/tcp_cong_kern.c
new file mode 100644
index 000000000000..dac15bce1fa9
--- /dev/null
+++ b/samples/bpf/tcp_cong_kern.c
@@ -0,0 +1,83 @@
+/* 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 congestion control to dctcp when both hosts are
+ * in the same datacenter (as deteremined by IPv6 prefix).
+ *
+ * Use load_sock_ops to load this BPF program.
+ */
+
+#include <uapi/linux/bpf.h>
+#include <uapi/linux/tcp.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_cong(struct bpf_sock_ops *skops)
+{
+        char cong[] = "dctcp";
+        int rv = 0;
+        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 if both hosts are in the same datacenter. For this
+         * example they are if the 1st 5.5 bytes in the IPv6 address
+         * are the same.
+         */
+        if (skops->family == AF_INET6 &&
+            skops->local_ip6[0] == skops->remote_ip6[0] &&
+            (bpf_ntohl(skops->local_ip6[1]) & 0xfff00000) ==
+            (bpf_ntohl(skops->remote_ip6[1]) & 0xfff00000)) {
+                switch (op) {
+                case BPF_SOCK_OPS_NEEDS_ECN:
+                        rv = 1;
+                        break;
+                case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
+                        rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
+                                            cong, sizeof(cong));
+                        break;
+                case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+                        rv = bpf_setsockopt(skops, SOL_TCP, TCP_CONGESTION,
+                                            cong, sizeof(cong));
+                        break;
+                default:
+                        rv = -1;
+                }
+        } else {
+                rv = -1;
+        }
+#ifdef DEBUG
+        bpf_printk("Returning %d\n", rv);
+#endif
+        skops->reply = rv;
+        return 1;
+}
+char _license[] SEC("license") = "GPL";