Merge branch 'bpf-tcp-rtt-hook'

Stanislav Fomichev says:

====================
Congestion control team would like to have a periodic callback to
track some TCP statistics. Let's add a sock_ops callback that can be
selectively enabled on a socket by socket basis and is executed for
every RTT. BPF program frequency can be further controlled by calling
bpf_ktime_get_ns and bailing out early.

I run neper tcp_stream and tcp_rr tests with the sample program
from the last patch and didn't observe any noticeable performance
difference.

v2:
* add a comment about second accept() in selftest (Yonghong Song)
* refer to tcp_bpf.readme in sample program (Yonghong Song)
====================
Suggested-by: NEric Dumazet <edumazet@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Priyaranjan Jha <priyarjha@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: NSoheil Hassas Yeganeh <soheil@google.com>
Acked-by: NYuchung Cheng <ycheng@google.com>
Acked-by: NYonghong Song <yhs@fb.com>
Acked-by: NLawrence Brakmo <brakmo@fb.com>
Signed-off-by: NDaniel Borkmann <daniel@iogearbox.net>

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

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
@@ -3072,6 +3073,12 @@ struct bpf_tcp_sock {
 				 * sum(delta(snd_una)), or how many bytes
 				 * were acked.
 				 */
+	__u32 dsack_dups;	/* RFC4898 tcpEStatsStackDSACKDups
+				 * total number of DSACK blocks received
+				 */
+	__u32 delivered;	/* Total data packets delivered incl. rexmits */
+	__u32 delivered_ce;	/* Like the above but only ECE marked packets */
+	__u32 icsk_retransmits;	/* Number of unrecovered [RTO] timeouts */
 };
 
 struct bpf_sock_tuple {
@@ -3314,7 +3321,8 @@ 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 +3377,8 @@ 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

net/core/filter.c

@@ -5194,54 +5194,6 @@ static const struct bpf_func_proto bpf_lwt_seg6_adjust_srh_proto = {
 };
 #endif /* CONFIG_IPV6_SEG6_BPF */
 
-#define CONVERT_COMMON_TCP_SOCK_FIELDS(md_type, CONVERT)		\
-do {									\
-	switch (si->off) {						\
-	case offsetof(md_type, snd_cwnd):				\
-		CONVERT(snd_cwnd); break;				\
-	case offsetof(md_type, srtt_us):				\
-		CONVERT(srtt_us); break;				\
-	case offsetof(md_type, snd_ssthresh):				\
-		CONVERT(snd_ssthresh); break;				\
-	case offsetof(md_type, rcv_nxt):				\
-		CONVERT(rcv_nxt); break;				\
-	case offsetof(md_type, snd_nxt):				\
-		CONVERT(snd_nxt); break;				\
-	case offsetof(md_type, snd_una):				\
-		CONVERT(snd_una); break;				\
-	case offsetof(md_type, mss_cache):				\
-		CONVERT(mss_cache); break;				\
-	case offsetof(md_type, ecn_flags):				\
-		CONVERT(ecn_flags); break;				\
-	case offsetof(md_type, rate_delivered):				\
-		CONVERT(rate_delivered); break;				\
-	case offsetof(md_type, rate_interval_us):			\
-		CONVERT(rate_interval_us); break;			\
-	case offsetof(md_type, packets_out):				\
-		CONVERT(packets_out); break;				\
-	case offsetof(md_type, retrans_out):				\
-		CONVERT(retrans_out); break;				\
-	case offsetof(md_type, total_retrans):				\
-		CONVERT(total_retrans); break;				\
-	case offsetof(md_type, segs_in):				\
-		CONVERT(segs_in); break;				\
-	case offsetof(md_type, data_segs_in):				\
-		CONVERT(data_segs_in); break;				\
-	case offsetof(md_type, segs_out):				\
-		CONVERT(segs_out); break;				\
-	case offsetof(md_type, data_segs_out):				\
-		CONVERT(data_segs_out); break;				\
-	case offsetof(md_type, lost_out):				\
-		CONVERT(lost_out); break;				\
-	case offsetof(md_type, sacked_out):				\
-		CONVERT(sacked_out); break;				\
-	case offsetof(md_type, bytes_received):				\
-		CONVERT(bytes_received); break;				\
-	case offsetof(md_type, bytes_acked):				\
-		CONVERT(bytes_acked); break;				\
-	}								\
-} while (0)
-
 #ifdef CONFIG_INET
 static struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
 			      int dif, int sdif, u8 family, u8 proto)
@@ -5592,7 +5544,8 @@ static const struct bpf_func_proto bpf_sock_addr_sk_lookup_udp_proto = {
 bool bpf_tcp_sock_is_valid_access(int off, int size, enum bpf_access_type type,
 				  struct bpf_insn_access_aux *info)
 {
-	if (off < 0 || off >= offsetofend(struct bpf_tcp_sock, bytes_acked))
+	if (off < 0 || off >= offsetofend(struct bpf_tcp_sock,
+					  icsk_retransmits))
 		return false;
 
 	if (off % size != 0)
@@ -5623,8 +5576,19 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
 				      offsetof(struct tcp_sock, FIELD)); \
 	} while (0)
 
-	CONVERT_COMMON_TCP_SOCK_FIELDS(struct bpf_tcp_sock,
-				       BPF_TCP_SOCK_GET_COMMON);
+#define BPF_INET_SOCK_GET_COMMON(FIELD)					\
+	do {								\
+		BUILD_BUG_ON(FIELD_SIZEOF(struct inet_connection_sock,	\
+					  FIELD) >			\
+			     FIELD_SIZEOF(struct bpf_tcp_sock, FIELD));	\
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			\
+					struct inet_connection_sock,	\
+					FIELD),				\
+				      si->dst_reg, si->src_reg,		\
+				      offsetof(				\
+					struct inet_connection_sock,	\
+					FIELD));			\
+	} while (0)
 
 	if (insn > insn_buf)
 		return insn - insn_buf;
@@ -5640,6 +5604,81 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
 				      offsetof(struct tcp_sock, rtt_min) +
 				      offsetof(struct minmax_sample, v));
 		break;
+	case offsetof(struct bpf_tcp_sock, snd_cwnd):
+		BPF_TCP_SOCK_GET_COMMON(snd_cwnd);
+		break;
+	case offsetof(struct bpf_tcp_sock, srtt_us):
+		BPF_TCP_SOCK_GET_COMMON(srtt_us);
+		break;
+	case offsetof(struct bpf_tcp_sock, snd_ssthresh):
+		BPF_TCP_SOCK_GET_COMMON(snd_ssthresh);
+		break;
+	case offsetof(struct bpf_tcp_sock, rcv_nxt):
+		BPF_TCP_SOCK_GET_COMMON(rcv_nxt);
+		break;
+	case offsetof(struct bpf_tcp_sock, snd_nxt):
+		BPF_TCP_SOCK_GET_COMMON(snd_nxt);
+		break;
+	case offsetof(struct bpf_tcp_sock, snd_una):
+		BPF_TCP_SOCK_GET_COMMON(snd_una);
+		break;
+	case offsetof(struct bpf_tcp_sock, mss_cache):
+		BPF_TCP_SOCK_GET_COMMON(mss_cache);
+		break;
+	case offsetof(struct bpf_tcp_sock, ecn_flags):
+		BPF_TCP_SOCK_GET_COMMON(ecn_flags);
+		break;
+	case offsetof(struct bpf_tcp_sock, rate_delivered):
+		BPF_TCP_SOCK_GET_COMMON(rate_delivered);
+		break;
+	case offsetof(struct bpf_tcp_sock, rate_interval_us):
+		BPF_TCP_SOCK_GET_COMMON(rate_interval_us);
+		break;
+	case offsetof(struct bpf_tcp_sock, packets_out):
+		BPF_TCP_SOCK_GET_COMMON(packets_out);
+		break;
+	case offsetof(struct bpf_tcp_sock, retrans_out):
+		BPF_TCP_SOCK_GET_COMMON(retrans_out);
+		break;
+	case offsetof(struct bpf_tcp_sock, total_retrans):
+		BPF_TCP_SOCK_GET_COMMON(total_retrans);
+		break;
+	case offsetof(struct bpf_tcp_sock, segs_in):
+		BPF_TCP_SOCK_GET_COMMON(segs_in);
+		break;
+	case offsetof(struct bpf_tcp_sock, data_segs_in):
+		BPF_TCP_SOCK_GET_COMMON(data_segs_in);
+		break;
+	case offsetof(struct bpf_tcp_sock, segs_out):
+		BPF_TCP_SOCK_GET_COMMON(segs_out);
+		break;
+	case offsetof(struct bpf_tcp_sock, data_segs_out):
+		BPF_TCP_SOCK_GET_COMMON(data_segs_out);
+		break;
+	case offsetof(struct bpf_tcp_sock, lost_out):
+		BPF_TCP_SOCK_GET_COMMON(lost_out);
+		break;
+	case offsetof(struct bpf_tcp_sock, sacked_out):
+		BPF_TCP_SOCK_GET_COMMON(sacked_out);
+		break;
+	case offsetof(struct bpf_tcp_sock, bytes_received):
+		BPF_TCP_SOCK_GET_COMMON(bytes_received);
+		break;
+	case offsetof(struct bpf_tcp_sock, bytes_acked):
+		BPF_TCP_SOCK_GET_COMMON(bytes_acked);
+		break;
+	case offsetof(struct bpf_tcp_sock, dsack_dups):
+		BPF_TCP_SOCK_GET_COMMON(dsack_dups);
+		break;
+	case offsetof(struct bpf_tcp_sock, delivered):
+		BPF_TCP_SOCK_GET_COMMON(delivered);
+		break;
+	case offsetof(struct bpf_tcp_sock, delivered_ce):
+		BPF_TCP_SOCK_GET_COMMON(delivered_ce);
+		break;
+	case offsetof(struct bpf_tcp_sock, icsk_retransmits):
+		BPF_INET_SOCK_GET_COMMON(icsk_retransmits);
+		break;
 	}
 
 	return insn - insn_buf;
@@ -7913,9 +7952,6 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 			SOCK_OPS_GET_FIELD(BPF_FIELD, OBJ_FIELD, OBJ);	      \
 	} while (0)
 
-	CONVERT_COMMON_TCP_SOCK_FIELDS(struct bpf_sock_ops,
-				       SOCK_OPS_GET_TCP_SOCK_FIELD);
-
 	if (insn > insn_buf)
 		return insn - insn_buf;
 
@@ -8085,6 +8121,69 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		SOCK_OPS_GET_OR_SET_FIELD(sk_txhash, sk_txhash,
 					  struct sock, type);
 		break;
+	case offsetof(struct bpf_sock_ops, snd_cwnd):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(snd_cwnd);
+		break;
+	case offsetof(struct bpf_sock_ops, srtt_us):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(srtt_us);
+		break;
+	case offsetof(struct bpf_sock_ops, snd_ssthresh):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(snd_ssthresh);
+		break;
+	case offsetof(struct bpf_sock_ops, rcv_nxt):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(rcv_nxt);
+		break;
+	case offsetof(struct bpf_sock_ops, snd_nxt):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(snd_nxt);
+		break;
+	case offsetof(struct bpf_sock_ops, snd_una):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(snd_una);
+		break;
+	case offsetof(struct bpf_sock_ops, mss_cache):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(mss_cache);
+		break;
+	case offsetof(struct bpf_sock_ops, ecn_flags):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(ecn_flags);
+		break;
+	case offsetof(struct bpf_sock_ops, rate_delivered):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(rate_delivered);
+		break;
+	case offsetof(struct bpf_sock_ops, rate_interval_us):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(rate_interval_us);
+		break;
+	case offsetof(struct bpf_sock_ops, packets_out):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(packets_out);
+		break;
+	case offsetof(struct bpf_sock_ops, retrans_out):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(retrans_out);
+		break;
+	case offsetof(struct bpf_sock_ops, total_retrans):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(total_retrans);
+		break;
+	case offsetof(struct bpf_sock_ops, segs_in):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(segs_in);
+		break;
+	case offsetof(struct bpf_sock_ops, data_segs_in):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(data_segs_in);
+		break;
+	case offsetof(struct bpf_sock_ops, segs_out):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(segs_out);
+		break;
+	case offsetof(struct bpf_sock_ops, data_segs_out):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(data_segs_out);
+		break;
+	case offsetof(struct bpf_sock_ops, lost_out):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(lost_out);
+		break;
+	case offsetof(struct bpf_sock_ops, sacked_out):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(sacked_out);
+		break;
+	case offsetof(struct bpf_sock_ops, bytes_received):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(bytes_received);
+		break;
+	case offsetof(struct bpf_sock_ops, bytes_acked):
+		SOCK_OPS_GET_TCP_SOCK_FIELD(bytes_acked);
+		break;
 	case offsetof(struct bpf_sock_ops, sk):
 		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
 						struct bpf_sock_ops_kern,

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);
 }

samples/bpf/Makefile

@@ -154,6 +154,7 @@ always += tcp_iw_kern.o
 always += tcp_clamp_kern.o
 always += tcp_basertt_kern.o
 always += tcp_tos_reflect_kern.o
+always += tcp_dumpstats_kern.o
 always += xdp_redirect_kern.o
 always += xdp_redirect_map_kern.o
 always += xdp_redirect_cpu_kern.o

samples/bpf/tcp_bpf.readme

@@ -25,4 +25,4 @@ attached to the cgroupv2).
 
 To remove (unattach) a socket_ops BPF program from a cgroupv2:
 
-  bpftool cgroup attach /tmp/cgroupv2/foo sock_ops pinned /sys/fs/bpf/tcp_prog
+  bpftool cgroup detach /tmp/cgroupv2/foo sock_ops pinned /sys/fs/bpf/tcp_prog

samples/bpf/tcp_dumpstats_kern.c

+// SPDX-License-Identifier: GPL-2.0
+/* Refer to samples/bpf/tcp_bpf.readme for the instructions on
+ * how to run this sample program.
+ */
+#include <linux/bpf.h>
+
+#include "bpf_helpers.h"
+#include "bpf_endian.h"
+
+#define INTERVAL			1000000000ULL
+
+int _version SEC("version") = 1;
+char _license[] SEC("license") = "GPL";
+
+struct {
+	__u32 type;
+	__u32 map_flags;
+	int *key;
+	__u64 *value;
+} bpf_next_dump SEC(".maps") = {
+	.type = BPF_MAP_TYPE_SK_STORAGE,
+	.map_flags = BPF_F_NO_PREALLOC,
+};
+
+SEC("sockops")
+int _sockops(struct bpf_sock_ops *ctx)
+{
+	struct bpf_tcp_sock *tcp_sk;
+	struct bpf_sock *sk;
+	__u64 *next_dump;
+	__u64 now;
+
+	switch (ctx->op) {
+	case BPF_SOCK_OPS_TCP_CONNECT_CB:
+		bpf_sock_ops_cb_flags_set(ctx, BPF_SOCK_OPS_RTT_CB_FLAG);
+		return 1;
+	case BPF_SOCK_OPS_RTT_CB:
+		break;
+	default:
+		return 1;
+	}
+
+	sk = ctx->sk;
+	if (!sk)
+		return 1;
+
+	next_dump = bpf_sk_storage_get(&bpf_next_dump, sk, 0,
+				       BPF_SK_STORAGE_GET_F_CREATE);
+	if (!next_dump)
+		return 1;
+
+	now = bpf_ktime_get_ns();
+	if (now < *next_dump)
+		return 1;
+
+	tcp_sk = bpf_tcp_sock(sk);
+	if (!tcp_sk)
+		return 1;
+
+	*next_dump = now + INTERVAL;
+
+	bpf_printk("dsack_dups=%u delivered=%u\n",
+		   tcp_sk->dsack_dups, tcp_sk->delivered);
+	bpf_printk("delivered_ce=%u icsk_retransmits=%u\n",
+		   tcp_sk->delivered_ce, tcp_sk->icsk_retransmits);
+
+	return 1;
+}

tools/include/uapi/linux/bpf.h

@@ -1767,6 +1767,7 @@ 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
@@ -3069,6 +3070,12 @@ struct bpf_tcp_sock {
 				 * sum(delta(snd_una)), or how many bytes
 				 * were acked.
 				 */
+	__u32 dsack_dups;	/* RFC4898 tcpEStatsStackDSACKDups
+				 * total number of DSACK blocks received
+				 */
+	__u32 delivered;	/* Total data packets delivered incl. rexmits */
+	__u32 delivered_ce;	/* Like the above but only ECE marked packets */
+	__u32 icsk_retransmits;	/* Number of unrecovered [RTO] timeouts */
 };
 
 struct bpf_sock_tuple {
@@ -3311,7 +3318,8 @@ 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
 							 */
 
@@ -3366,6 +3374,8 @@ 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

tools/testing/selftests/bpf/Makefile

@@ -27,7 +27,7 @@ TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test
 	test_cgroup_storage test_select_reuseport test_section_names \
 	test_netcnt test_tcpnotify_user test_sock_fields test_sysctl test_hashmap \
 	test_btf_dump test_cgroup_attach xdping test_sockopt test_sockopt_sk \
-	test_sockopt_multi
+	test_sockopt_multi test_tcp_rtt
 
 BPF_OBJ_FILES = $(patsubst %.c,%.o, $(notdir $(wildcard progs/*.c)))
 TEST_GEN_FILES = $(BPF_OBJ_FILES)
@@ -107,6 +107,7 @@ $(OUTPUT)/test_cgroup_attach: cgroup_helpers.c
 $(OUTPUT)/test_sockopt: cgroup_helpers.c
 $(OUTPUT)/test_sockopt_sk: cgroup_helpers.c
 $(OUTPUT)/test_sockopt_multi: cgroup_helpers.c
+$(OUTPUT)/test_tcp_rtt: cgroup_helpers.c
 
 .PHONY: force
 

tools/testing/selftests/bpf/progs/tcp_rtt.c

+// SPDX-License-Identifier: GPL-2.0
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+__u32 _version SEC("version") = 1;
+
+struct tcp_rtt_storage {
+	__u32 invoked;
+	__u32 dsack_dups;
+	__u32 delivered;
+	__u32 delivered_ce;
+	__u32 icsk_retransmits;
+};
+
+struct bpf_map_def SEC("maps") socket_storage_map = {
+	.type = BPF_MAP_TYPE_SK_STORAGE,
+	.key_size = sizeof(int),
+	.value_size = sizeof(struct tcp_rtt_storage),
+	.map_flags = BPF_F_NO_PREALLOC,
+};
+BPF_ANNOTATE_KV_PAIR(socket_storage_map, int, struct tcp_rtt_storage);
+
+SEC("sockops")
+int _sockops(struct bpf_sock_ops *ctx)
+{
+	struct tcp_rtt_storage *storage;
+	struct bpf_tcp_sock *tcp_sk;
+	int op = (int) ctx->op;
+	struct bpf_sock *sk;
+
+	sk = ctx->sk;
+	if (!sk)
+		return 1;
+
+	storage = bpf_sk_storage_get(&socket_storage_map, sk, 0,
+				     BPF_SK_STORAGE_GET_F_CREATE);
+	if (!storage)
+		return 1;
+
+	if (op == BPF_SOCK_OPS_TCP_CONNECT_CB) {
+		bpf_sock_ops_cb_flags_set(ctx, BPF_SOCK_OPS_RTT_CB_FLAG);
+		return 1;
+	}
+
+	if (op != BPF_SOCK_OPS_RTT_CB)
+		return 1;
+
+	tcp_sk = bpf_tcp_sock(sk);
+	if (!tcp_sk)
+		return 1;
+
+	storage->invoked++;
+
+	storage->dsack_dups = tcp_sk->dsack_dups;
+	storage->delivered = tcp_sk->delivered;
+	storage->delivered_ce = tcp_sk->delivered_ce;
+	storage->icsk_retransmits = tcp_sk->icsk_retransmits;
+
+	return 1;
+}

tools/testing/selftests/bpf/test_tcp_rtt.c

+// SPDX-License-Identifier: GPL-2.0
+#include <error.h>
+#include <errno.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <pthread.h>
+
+#include <linux/filter.h>
+#include <bpf/bpf.h>
+#include <bpf/libbpf.h>
+
+#include "bpf_rlimit.h"
+#include "bpf_util.h"
+#include "cgroup_helpers.h"
+
+#define CG_PATH                                "/tcp_rtt"
+
+struct tcp_rtt_storage {
+	__u32 invoked;
+	__u32 dsack_dups;
+	__u32 delivered;
+	__u32 delivered_ce;
+	__u32 icsk_retransmits;
+};
+
+static void send_byte(int fd)
+{
+	char b = 0x55;
+
+	if (write(fd, &b, sizeof(b)) != 1)
+		error(1, errno, "Failed to send single byte");
+}
+
+static int verify_sk(int map_fd, int client_fd, const char *msg, __u32 invoked,
+		     __u32 dsack_dups, __u32 delivered, __u32 delivered_ce,
+		     __u32 icsk_retransmits)
+{
+	int err = 0;
+	struct tcp_rtt_storage val;
+
+	if (bpf_map_lookup_elem(map_fd, &client_fd, &val) < 0)
+		error(1, errno, "Failed to read socket storage");
+
+	if (val.invoked != invoked) {
+		log_err("%s: unexpected bpf_tcp_sock.invoked %d != %d",
+			msg, val.invoked, invoked);
+		err++;
+	}
+
+	if (val.dsack_dups != dsack_dups) {
+		log_err("%s: unexpected bpf_tcp_sock.dsack_dups %d != %d",
+			msg, val.dsack_dups, dsack_dups);
+		err++;
+	}
+
+	if (val.delivered != delivered) {
+		log_err("%s: unexpected bpf_tcp_sock.delivered %d != %d",
+			msg, val.delivered, delivered);
+		err++;
+	}
+
+	if (val.delivered_ce != delivered_ce) {
+		log_err("%s: unexpected bpf_tcp_sock.delivered_ce %d != %d",
+			msg, val.delivered_ce, delivered_ce);
+		err++;
+	}
+
+	if (val.icsk_retransmits != icsk_retransmits) {
+		log_err("%s: unexpected bpf_tcp_sock.icsk_retransmits %d != %d",
+			msg, val.icsk_retransmits, icsk_retransmits);
+		err++;
+	}
+
+	return err;
+}
+
+static int connect_to_server(int server_fd)
+{
+	struct sockaddr_storage addr;
+	socklen_t len = sizeof(addr);
+	int fd;
+
+	fd = socket(AF_INET, SOCK_STREAM, 0);
+	if (fd < 0) {
+		log_err("Failed to create client socket");
+		return -1;
+	}
+
+	if (getsockname(server_fd, (struct sockaddr *)&addr, &len)) {
+		log_err("Failed to get server addr");
+		goto out;
+	}
+
+	if (connect(fd, (const struct sockaddr *)&addr, len) < 0) {
+		log_err("Fail to connect to server");
+		goto out;
+	}
+
+	return fd;
+
+out:
+	close(fd);
+	return -1;
+}
+
+static int run_test(int cgroup_fd, int server_fd)
+{
+	struct bpf_prog_load_attr attr = {
+		.prog_type = BPF_PROG_TYPE_SOCK_OPS,
+		.file = "./tcp_rtt.o",
+		.expected_attach_type = BPF_CGROUP_SOCK_OPS,
+	};
+	struct bpf_object *obj;
+	struct bpf_map *map;
+	int client_fd;
+	int prog_fd;
+	int map_fd;
+	int err;
+
+	err = bpf_prog_load_xattr(&attr, &obj, &prog_fd);
+	if (err) {
+		log_err("Failed to load BPF object");
+		return -1;
+	}
+
+	map = bpf_map__next(NULL, obj);
+	map_fd = bpf_map__fd(map);
+
+	err = bpf_prog_attach(prog_fd, cgroup_fd, BPF_CGROUP_SOCK_OPS, 0);
+	if (err) {
+		log_err("Failed to attach BPF program");
+		goto close_bpf_object;
+	}
+
+	client_fd = connect_to_server(server_fd);
+	if (client_fd < 0) {
+		err = -1;
+		goto close_bpf_object;
+	}
+
+	err += verify_sk(map_fd, client_fd, "syn-ack",
+			 /*invoked=*/1,
+			 /*dsack_dups=*/0,
+			 /*delivered=*/1,
+			 /*delivered_ce=*/0,
+			 /*icsk_retransmits=*/0);
+
+	send_byte(client_fd);
+
+	err += verify_sk(map_fd, client_fd, "first payload byte",
+			 /*invoked=*/2,
+			 /*dsack_dups=*/0,
+			 /*delivered=*/2,
+			 /*delivered_ce=*/0,
+			 /*icsk_retransmits=*/0);
+
+	close(client_fd);
+
+close_bpf_object:
+	bpf_object__close(obj);
+	return err;
+}
+
+static int start_server(void)
+{
+	struct sockaddr_in addr = {
+		.sin_family = AF_INET,
+		.sin_addr.s_addr = htonl(INADDR_LOOPBACK),
+	};
+	int fd;
+
+	fd = socket(AF_INET, SOCK_STREAM, 0);
+	if (fd < 0) {
+		log_err("Failed to create server socket");
+		return -1;
+	}
+
+	if (bind(fd, (const struct sockaddr *)&addr, sizeof(addr)) < 0) {
+		log_err("Failed to bind socket");
+		close(fd);
+		return -1;
+	}
+
+	return fd;
+}
+
+static void *server_thread(void *arg)
+{
+	struct sockaddr_storage addr;
+	socklen_t len = sizeof(addr);
+	int fd = *(int *)arg;
+	int client_fd;
+
+	if (listen(fd, 1) < 0)
+		error(1, errno, "Failed to listed on socket");
+
+	client_fd = accept(fd, (struct sockaddr *)&addr, &len);
+	if (client_fd < 0)
+		error(1, errno, "Failed to accept client");
+
+	/* Wait for the next connection (that never arrives)
+	 * to keep this thread alive to prevent calling
+	 * close() on client_fd.
+	 */
+	if (accept(fd, (struct sockaddr *)&addr, &len) >= 0)
+		error(1, errno, "Unexpected success in second accept");
+
+	close(client_fd);
+
+	return NULL;
+}
+
+int main(int args, char **argv)
+{
+	int server_fd, cgroup_fd;
+	int err = EXIT_SUCCESS;
+	pthread_t tid;
+
+	if (setup_cgroup_environment())
+		goto cleanup_obj;
+
+	cgroup_fd = create_and_get_cgroup(CG_PATH);
+	if (cgroup_fd < 0)
+		goto cleanup_cgroup_env;
+
+	if (join_cgroup(CG_PATH))
+		goto cleanup_cgroup;
+
+	server_fd = start_server();
+	if (server_fd < 0) {
+		err = EXIT_FAILURE;
+		goto cleanup_cgroup;
+	}
+
+	pthread_create(&tid, NULL, server_thread, (void *)&server_fd);
+
+	if (run_test(cgroup_fd, server_fd))
+		err = EXIT_FAILURE;
+
+	close(server_fd);
+
+	printf("test_sockopt_sk: %s\n",
+	       err == EXIT_SUCCESS ? "PASSED" : "FAILED");
+
+cleanup_cgroup:
+	close(cgroup_fd);
+cleanup_cgroup_env:
+	cleanup_cgroup_environment();
+cleanup_obj:
+	return err;
+}