Subject: [RFC PATCH net-next v2 03/15] bpf: Support for per connection SYN/SYN-ACK RTOs

From: Lawrence Brakmo <[email-masked]>
Date: Thu, 15 Jun 2017 13:08:32 -0700

This patch adds support for setting a per connection SYN and
SYN_ACK RTOs from within a BPF_SOCKET_OPS program. For example,
to set small RTOs when it is known both hosts are within a
datacenter.

Signed-off-by: Lawrence Brakmo <[email-masked]>
---
 include/net/tcp.h        | 11 +++++++++++
 include/uapi/linux/bpf.h |  3 +++
 net/ipv4/tcp_input.c     |  3 ++-
 net/ipv4/tcp_output.c    |  2 +-
 4 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 9ad0d80..a726486 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2018,4 +2018,15 @@ static inline int tcp_call_bpf(struct sock *sk, bool is_req_sock, int op)
 }
 #endif
 
+static inline u32 tcp_timeout_init(struct sock *sk, bool is_req_sock)
+{
+	int timeout;
+
+	timeout = tcp_call_bpf(sk, is_req_sock, BPF_SOCKET_OPS_TIMEOUT_INIT);
+
+	if (timeout <= 0)
+		timeout = TCP_TIMEOUT_INIT;
+	return timeout;
+}
+
 #endif	/* _TCP_H */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1540336..039f327 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -746,6 +746,9 @@ struct bpf_socket_ops {
  */
 enum {
 	BPF_SOCKET_OPS_VOID,
+	BPF_SOCKET_OPS_TIMEOUT_INIT,	/* Should return SYN-RTO value to use or
+					 * -1 if default value should be used
+					 */
 };
 
 #endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2ab7e2f..0867b05 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6406,7 +6406,8 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 	} else {
 		tcp_rsk(req)->tfo_listener = false;
 		if (!want_cookie)
-			inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+			inet_csk_reqsk_queue_hash_add(sk, req,
+				tcp_timeout_init((struct sock *)req, true));
 		af_ops->send_synack(sk, dst, &fl, req, &foc,
 				    !want_cookie ? TCP_SYNACK_NORMAL :
 						   TCP_SYNACK_COOKIE);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 9a9c395..5e478a1 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3327,7 +3327,7 @@ static void tcp_connect_init(struct sock *sk)
 	tp->rcv_wup = tp->rcv_nxt;
 	tp->copied_seq = tp->rcv_nxt;
 
-	inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
+	inet_csk(sk)->icsk_rto = tcp_timeout_init(sk, false);
 	inet_csk(sk)->icsk_retransmits = 0;
 	tcp_clear_retrans(tp);
 }
-- 
2.9.3