From: Lawrence Brakmo <brakmo@fb.com>
Date: Fri, 30 Jun 2017 20:02:53 -0700
Subject: bpf: Adds support for setting sndcwnd clamp
Patch-mainline: v4.13-rc1
Git-commit: 13bf96411ad2bd162a4f9470d58c6bb579c96e21
References: bsc#1109837

Adds a new bpf_setsockopt for TCP sockets, TCP_BPF_SNDCWND_CLAMP, which
sets the initial congestion window. It is useful to limit the sndcwnd
when the host are close to each other (small RTT).

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 include/uapi/linux/bpf.h |    1 +
 net/core/filter.c        |    7 +++++++
 2 files changed, 8 insertions(+)

--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -781,5 +781,6 @@ enum {
 };
 
 #define TCP_BPF_IW		1001	/* Set TCP initial congestion window */
+#define TCP_BPF_SNDCWND_CLAMP	1002	/* Set sndcwnd_clamp */
 
 #endif /* _UAPI__LINUX_BPF_H__ */
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2746,6 +2746,13 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_so
 				else
 					tp->snd_cwnd = val;
 				break;
+			case TCP_BPF_SNDCWND_CLAMP:
+				if (val <= 0) {
+					ret = -EINVAL;
+				} else {
+					tp->snd_cwnd_clamp = val;
+					tp->snd_ssthresh = val;
+				}
 			default:
 				ret = -EINVAL;
 			}