tcp: make tcp_v{4,6}_send_check() static

tcp_v{4,6}_send_check() are only called from tcp_output.c
and should be made static so that the compiler does not need
to put an out of line copy of them.

Remove (struct inet_connection_sock_af_ops) send_check field
and use instead @net_header_len.

Move @net_header_len close to @queue_xmit for data locality
as both are used in TCP tx fast path.

$ scripts/bloat-o-meter -t vmlinux.2 vmlinux.3
add/remove: 0/2 grow/shrink: 0/3 up/down: 0/-172 (-172)
Function                                     old     new   delta
__tcp_transmit_skb                          3426    3423      -3
tcp_v4_send_check                            136     132      -4
mptcp_subflow_init                           777     763     -14
__pfx_tcp_v6_send_check                       16       -     -16
tcp_v6_send_check                            135       -    -135
Total: Before=25143196, After=25143024, chg -0.00%

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260223100729.3761597-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/inet_connection_sock.h

@@ -34,7 +34,7 @@ struct tcp_congestion_ops;
  */
 struct inet_connection_sock_af_ops {
 	int	    (*queue_xmit)(struct sock *sk, struct sk_buff *skb, struct flowi *fl);
-	void	    (*send_check)(struct sock *sk, struct sk_buff *skb);
+	u16	    net_header_len;
 	int	    (*rebuild_header)(struct sock *sk);
 	void	    (*sk_rx_dst_set)(struct sock *sk, const struct sk_buff *skb);
 	int	    (*conn_request)(struct sock *sk, struct sk_buff *skb);
@@ -43,7 +43,6 @@ struct inet_connection_sock_af_ops {
 				      struct dst_entry *dst,
 				      struct request_sock *req_unhash,
 				      bool *own_req);
-	u16	    net_header_len;
 	int	    (*setsockopt)(struct sock *sk, int level, int optname,
 				  sockptr_t optval, unsigned int optlen);
 	int	    (*getsockopt)(struct sock *sk, int level, int optname,

include/net/tcp.h

@@ -531,7 +531,6 @@ u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
  *	TCP v4 functions exported for the inet6 API
  */
 
-void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb);
 void tcp_v4_mtu_reduced(struct sock *sk);
 void tcp_req_err(struct sock *sk, u32 seq, bool abort);
 void tcp_ld_RTO_revert(struct sock *sk, u32 seq);
@@ -1132,8 +1131,6 @@ static inline int tcp_v6_sdif(const struct sk_buff *skb)
 
 extern const struct inet_connection_sock_af_ops ipv6_specific;
 
-void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb);
-
 INDIRECT_CALLABLE_DECLARE(int tcp_v6_rcv(struct sk_buff *skb));
 void tcp_v6_early_demux(struct sk_buff *skb);
 

net/ipv4/tcp_ipv4.c

@@ -2405,7 +2405,6 @@ EXPORT_IPV6_MOD(inet_sk_rx_dst_set);
 
 const struct inet_connection_sock_af_ops ipv4_specific = {
 	.queue_xmit	   = ip_queue_xmit,
-	.send_check	   = tcp_v4_send_check,
 	.rebuild_header	   = inet_sk_rebuild_header,
 	.sk_rx_dst_set	   = inet_sk_rx_dst_set,
 	.conn_request	   = tcp_v4_conn_request,

net/ipv4/tcp_output.c

@@ -1498,22 +1498,20 @@ INDIRECT_CALLABLE_DECLARE(int ip_queue_xmit(struct sock *sk, struct sk_buff *skb
 INDIRECT_CALLABLE_DECLARE(int inet6_csk_xmit(struct sock *sk, struct sk_buff *skb, struct flowi *fl));
 
 /* This routine computes an IPv4 TCP checksum. */
-void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb)
+static void tcp_v4_send_check(struct sock *sk, struct sk_buff *skb)
 {
 	const struct inet_sock *inet = inet_sk(sk);
 
 	__tcp_v4_send_check(skb, inet->inet_saddr, inet->inet_daddr);
 }
-EXPORT_IPV6_MOD(tcp_v4_send_check);
 
 #if IS_ENABLED(CONFIG_IPV6)
 #include <net/ip6_checksum.h>
 
-void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb)
+static void tcp_v6_send_check(struct sock *sk, struct sk_buff *skb)
 {
 	__tcp_v6_send_check(skb, &sk->sk_v6_rcv_saddr, &sk->sk_v6_daddr);
 }
-EXPORT_IPV6_MOD(tcp_v6_send_check);
 #endif
 
 /* This routine actually transmits TCP packets queued in by
@@ -1678,7 +1676,7 @@ static int __tcp_transmit_skb(struct sock *sk, struct sk_buff *skb,
 	bpf_skops_write_hdr_opt(sk, skb, NULL, NULL, 0, &opts);
 
 #if IS_ENABLED(CONFIG_IPV6)
-	if (likely(icsk->icsk_af_ops->send_check == tcp_v6_send_check))
+	if (likely(icsk->icsk_af_ops->net_header_len == sizeof(struct ipv6hdr)))
 		tcp_v6_send_check(sk, skb);
 	else
 #endif

net/ipv6/tcp_ipv6.c

@@ -2017,7 +2017,6 @@ static struct timewait_sock_ops tcp6_timewait_sock_ops = {
 
 const struct inet_connection_sock_af_ops ipv6_specific = {
 	.queue_xmit	   = inet6_csk_xmit,
-	.send_check	   = tcp_v6_send_check,
 	.rebuild_header	   = inet6_sk_rebuild_header,
 	.sk_rx_dst_set	   = inet6_sk_rx_dst_set,
 	.conn_request	   = tcp_v6_conn_request,
@@ -2049,7 +2048,6 @@ static const struct tcp_sock_af_ops tcp_sock_ipv6_specific = {
  */
 static const struct inet_connection_sock_af_ops ipv6_mapped = {
 	.queue_xmit	   = ip_queue_xmit,
-	.send_check	   = tcp_v4_send_check,
 	.rebuild_header	   = inet_sk_rebuild_header,
 	.sk_rx_dst_set	   = inet_sk_rx_dst_set,
 	.conn_request	   = tcp_v6_conn_request,

net/mptcp/subflow.c

@@ -2190,7 +2190,6 @@ void __init mptcp_subflow_init(void)
 
 	subflow_v6m_specific = subflow_v6_specific;
 	subflow_v6m_specific.queue_xmit = ipv4_specific.queue_xmit;
-	subflow_v6m_specific.send_check = ipv4_specific.send_check;
 	subflow_v6m_specific.net_header_len = ipv4_specific.net_header_len;
 	subflow_v6m_specific.mtu_reduced = ipv4_specific.mtu_reduced;
 	subflow_v6m_specific.rebuild_header = subflow_rebuild_header;

net/tls/tls_device_fallback.c

@@ -149,9 +149,6 @@ static int tls_enc_records(struct aead_request *aead_req,
 	return rc;
 }
 
-/* Can't use icsk->icsk_af_ops->send_check here because the ip addresses
- * might have been changed by NAT.
- */
 static void update_chksum(struct sk_buff *skb, int headln)
 {
 	struct tcphdr *th = tcp_hdr(skb);