netdev - [RFC PATCH net-next 2/2] TCP: pass accepted-TFO indication through getsockopt

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Message-ID: <3e9b638ad6846aff954a590dd87f764684a4ec8f.1741877016.git.jgh@exim.org>
Date: Thu, 13 Mar 2025 14:45:51 +0000
From: Jeremy Harris <jgh@...m.org>
To: netdev@...r.kernel.org
Cc: Jeremy Harris <jgh@...m.org>
Subject: [RFC PATCH net-next 2/2] TCP: pass accepted-TFO indication through getsockopt

Signed-off-by: Jeremy Harris <jgh@...m.org>
---
 include/uapi/linux/tcp.h | 1 +
 net/ipv4/tcp.c           | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index 32a27b4a5..e958a145d 100644
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -179,6 +179,7 @@ enum tcp_fastopen_client_fail {
 #define TCPI_OPT_ECN_SEEN	16 /* we received at least one packet with ECT */
 #define TCPI_OPT_SYN_DATA	32 /* SYN-ACK acked data in SYN sent or rcvd */
 #define TCPI_OPT_USEC_TS	64 /* usec timestamps */
+#define TCPI_OPT_TFO_SEEN	128 /* we accepted a Fast Open option on SYN */
 
 /*
  * Sender's congestion state indicating normal or abnormal situations
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 46951e749..407bdfb12 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4146,6 +4146,8 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
 		info->tcpi_options |= TCPI_OPT_SYN_DATA;
 	if (tp->tcp_usec_ts)
 		info->tcpi_options |= TCPI_OPT_USEC_TS;
+	if (tp->syn_fastopen_in)
+		info->tcpi_options |= TCPI_OPT_TFO_SEEN;
 
 	info->tcpi_rto = jiffies_to_usecs(icsk->icsk_rto);
 	info->tcpi_ato = jiffies_to_usecs(min_t(u32, icsk->icsk_ack.ato,
-- 
2.48.1