v4.19.13 snapshot.
diff --git a/samples/bpf/tcp_iw_kern.c b/samples/bpf/tcp_iw_kern.c
new file mode 100644
index 0000000..4ca5ecc
--- /dev/null
+++ b/samples/bpf/tcp_iw_kern.c
@@ -0,0 +1,90 @@
+/* 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 initial congestion window and initial receive
+ * window to 40 packets and send and receive buffers to 1.5MB. This
+ * would usually be done after doing appropriate checks that indicate
+ * the hosts are far enough away (i.e. large RTT).
+ *
+ * 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_iw(struct bpf_sock_ops *skops)
+{
+ int bufsize = 1500000;
+ int rwnd_init = 40;
+ int iw = 40;
+ 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 1;
+ }
+
+ op = (int) skops->op;
+
+#ifdef DEBUG
+ bpf_printk("BPF command: %d\n", op);
+#endif
+
+ /* Usually there would be a check to insure the hosts are far
+ * from each other so it makes sense to increase buffer sizes
+ */
+ switch (op) {
+ case BPF_SOCK_OPS_RWND_INIT:
+ rv = rwnd_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_IW, &iw,
+ sizeof(iw));
+ break;
+ case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
+ /* Set sndbuf and rcvbuf of passive connections */
+ 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;
+ }
+#ifdef DEBUG
+ bpf_printk("Returning %d\n", rv);
+#endif
+ skops->reply = rv;
+ return 1;
+}
+char _license[] SEC("license") = "GPL";