v4.19.13 snapshot.
diff --git a/samples/bpf/tcp_clamp_kern.c b/samples/bpf/tcp_clamp_kern.c
new file mode 100644
index 0000000..f4225c9
--- /dev/null
+++ b/samples/bpf/tcp_clamp_kern.c
@@ -0,0 +1,104 @@
+/* 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.
+ *
+ * Sample BPF program to set send and receive buffers to 150KB, sndcwnd clamp
+ * to 100 packets and SYN and SYN_ACK RTOs to 10ms when both hosts are within
+ * the same datacenter. For his example, we assume they are within the same
+ * datacenter when the first 5.5 bytes of their IPv6 addresses are the same.
+ *
+ * Use load_sock_ops to load this BPF program.
+ */
+
+#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"
+#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_clamp(struct bpf_sock_ops *skops)
+{
+ int bufsize = 150000;
+ int to_init = 10;
+ int clamp = 100;
+ 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) {
+ skops->reply = -1;
+ return 0;
+ }
+
+ op = (int) skops->op;
+
+#ifdef DEBUG
+ bpf_printk("BPF command: %d\n", op);
+#endif
+
+ /* Check that both hosts are within same datacenter. For this example
+ * it is the case when the first 5.5 bytes of their IPv6 addresses 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_TIMEOUT_INIT:
+ rv = to_init;
+ break;
+ case BPF_SOCK_OPS_TCP_CONNECT_CB:
+ /* Set sndbuf and rcvbuf of active connections */
+ rv = bpf_setsockopt(skops, SOL_SOCKET, SO_SNDBUF,
+ &bufsize, sizeof(bufsize));
+ rv += bpf_setsockopt(skops, SOL_SOCKET,
+ SO_RCVBUF, &bufsize,
+ sizeof(bufsize));
+ break;
+ case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
+ rv = bpf_setsockopt(skops, SOL_TCP,
+ TCP_BPF_SNDCWND_CLAMP,
+ &clamp, sizeof(clamp));
+ break;
+ case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+ /* Set sndbuf and rcvbuf of passive connections */
+ rv = bpf_setsockopt(skops, SOL_TCP,
+ TCP_BPF_SNDCWND_CLAMP,
+ &clamp, sizeof(clamp));
+ rv += bpf_setsockopt(skops, SOL_SOCKET,
+ SO_SNDBUF, &bufsize,
+ sizeof(bufsize));
+ rv += bpf_setsockopt(skops, SOL_SOCKET,
+ SO_RCVBUF, &bufsize,
+ sizeof(bufsize));
+ 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";