Subject: [PATCH bpf-next 1/8] bpf: add BPF_CGROUP_SOCK_OPS callback that is executed on every RTT

From: Stanislav Fomichev <[email-masked]>
Date: Mon, 1 Jul 2019 13:48:14 -0700

Performance impact should be minimal because it's under a new
BPF_SOCK_OPS_RTT_CB_FLAG flag that has to be explicitly enabled.

Suggested-by: Eric Dumazet <[email-masked]>
Cc: Eric Dumazet <[email-masked]>
Cc: Priyaranjan Jha <[email-masked]>
Cc: Yuchung Cheng <[email-masked]>
Cc: Soheil Hassas Yeganeh <[email-masked]>
Signed-off-by: Stanislav Fomichev <[email-masked]>
---
 include/net/tcp.h        | 8 ++++++++
 include/uapi/linux/bpf.h | 6 +++++-
 net/ipv4/tcp_input.c     | 4 ++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 9d36cc88d043..e16d8a3fd3b4 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2221,6 +2221,14 @@ static inline bool tcp_bpf_ca_needs_ecn(struct sock *sk)
 	return (tcp_call_bpf(sk, BPF_SOCK_OPS_NEEDS_ECN, 0, NULL) == 1);
 }
 
+static inline void tcp_bpf_rtt(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTT_CB_FLAG))
+		tcp_call_bpf(sk, BPF_SOCK_OPS_RTT_CB, 0, NULL);
+}
+
 #if IS_ENABLED(CONFIG_SMC)
 extern struct static_key_false tcp_have_smc;
 #endif
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index cffea1826a1f..9cdd0aaeba06 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1770,6 +1770,7 @@ union bpf_attr {
  * 		* **BPF_SOCK_OPS_RTO_CB_FLAG** (retransmission time out)
  * 		* **BPF_SOCK_OPS_RETRANS_CB_FLAG** (retransmission)
  * 		* **BPF_SOCK_OPS_STATE_CB_FLAG** (TCP state change)
+ * 		* **BPF_SOCK_OPS_RTT_CB_FLAG** (every RTT)
  *
  * 		Therefore, this function can be used to clear a callback flag by
  * 		setting the appropriate bit to zero. e.g. to disable the RTO
@@ -3314,7 +3315,8 @@ struct bpf_sock_ops {
 #define BPF_SOCK_OPS_RTO_CB_FLAG	(1<<0)
 #define BPF_SOCK_OPS_RETRANS_CB_FLAG	(1<<1)
 #define BPF_SOCK_OPS_STATE_CB_FLAG	(1<<2)
-#define BPF_SOCK_OPS_ALL_CB_FLAGS       0x7		/* Mask of all currently
+#define BPF_SOCK_OPS_RTT_CB_FLAG	(1<<3)
+#define BPF_SOCK_OPS_ALL_CB_FLAGS       0xF		/* Mask of all currently
 							 * supported cb flags
 							 */
 
@@ -3369,6 +3371,8 @@ enum {
 	BPF_SOCK_OPS_TCP_LISTEN_CB,	/* Called on listen(2), right after
 					 * socket transition to LISTEN state.
 					 */
+	BPF_SOCK_OPS_RTT_CB,		/* Called on every RTT.
+					 */
 };
 
 /* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index b71efeb0ae5b..c21e8a22fb3b 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -778,6 +778,8 @@ static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
 				tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
 			tp->rtt_seq = tp->snd_nxt;
 			tp->mdev_max_us = tcp_rto_min_us(sk);
+
+			tcp_bpf_rtt(sk);
 		}
 	} else {
 		/* no previous measure. */
@@ -786,6 +788,8 @@ static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
 		tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
 		tp->mdev_max_us = tp->rttvar_us;
 		tp->rtt_seq = tp->snd_nxt;
+
+		tcp_bpf_rtt(sk);
 	}
 	tp->srtt_us = max(1U, srtt);
 }
-- 
2.22.0.410.gd8fdbe21b5-goog