From: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>

Add 2-bit tcpi_ecn_mode feild within tcp_info to indicate which ECN
mode is negotiated: ECN_MODE_DISABLED, ECN_MODE_RFC3168, ECN_MODE_ACCECN,
or ECN_MODE_PENDING. This is done by utilizing available bits from
tcpi_accecn_opt_seen (reduced from 16 bits to 2 bits) and
tcpi_accecn_fail_mode (reduced from 16 bits to 4 bits).

Also, an extra 24-bit tcpi_options2 field is identified to represent
newer options and connection features, as all 8 bits of tcpi_options
field have been used.

Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs.com>
---
 include/uapi/linux/tcp.h | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index e35d416b..bac6e83f 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -226,6 +226,24 @@ enum tcp_ca_state {
 #define TCPF_CA_Loss	(1<<TCP_CA_Loss)
 };
 
+/* Values for tcpi_ecn_mode after negotiation */
+#define TCPI_ECN_MODE_DISABLED		0x0
+#define TCPI_ECN_MODE_RFC3168		0x1
+#define TCPI_ECN_MODE_ACCECN		0x2
+#define TCPI_ECN_MODE_PENDING		0x3
+
+/* Values for accecn_opt_seen */
+#define TCP_ACCECN_OPT_NOT_SEEN		0x0
+#define TCP_ACCECN_OPT_EMPTY_SEEN	0x1
+#define TCP_ACCECN_OPT_COUNTER_SEEN	0x2
+#define TCP_ACCECN_OPT_FAIL_SEEN	0x3
+
+/* Values for accecn_fail_mode */
+#define TCP_ACCECN_ACE_FAIL_SEND	BIT(0)
+#define TCP_ACCECN_ACE_FAIL_RECV	BIT(1)
+#define TCP_ACCECN_OPT_FAIL_SEND	BIT(2)
+#define TCP_ACCECN_OPT_FAIL_RECV	BIT(3)
+
 struct tcp_info {
 	__u8	tcpi_state;
 	__u8	tcpi_ca_state;
@@ -316,15 +334,17 @@ struct tcp_info {
 					 * in milliseconds, including any
 					 * unfinished recovery.
 					 */
-	__u32	tcpi_received_ce;    /* # of CE marks received */
+	__u32	tcpi_received_ce;    /* # of CE marked segments received */
 	__u32	tcpi_delivered_e1_bytes;  /* Accurate ECN byte counters */
 	__u32	tcpi_delivered_e0_bytes;
 	__u32	tcpi_delivered_ce_bytes;
 	__u32	tcpi_received_e1_bytes;
 	__u32	tcpi_received_e0_bytes;
 	__u32	tcpi_received_ce_bytes;
-	__u16	tcpi_accecn_fail_mode;
-	__u16	tcpi_accecn_opt_seen;
+	__u32	tcpi_ecn_mode:2,
+		tcpi_accecn_opt_seen:2,
+		tcpi_accecn_fail_mode:4,
+		tcpi_options2:24;
 };
 
 /* netlink attributes types for SCM_TIMESTAMPING_OPT_STATS */
-- 
2.34.1