[RFC PATCH net-next v2 14/15] bpf: Adds support for setting sndcwnd clamp

[Lawrence Brakmo <brakmo@fb.com>]

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>
---
 include/uapi/linux/bpf.h | 1 +
 net/core/filter.c        | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index ecb28e2..4d033eb 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -782,5 +782,6 @@ 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__ */
diff --git a/net/core/filter.c b/net/core/filter.c
index a1d9214..f484fef 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2733,6 +2733,13 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_socket_ops_kern *, bpf_socket,
 				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;
 			}
-- 
2.9.3