inet: preserve const qualifier in inet_csk()

We can change inet_csk() to propagate its argument const qualifier,
thanks to container_of_const().

We have to fix few places that had mistakes, like tcp_bound_rto().
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20240329144931.295800-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/espintcp.h

@@ -32,7 +32,7 @@ struct espintcp_ctx {
 
 static inline struct espintcp_ctx *espintcp_getctx(const struct sock *sk)
 {
-	struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 	/* RCU is only needed for diag */
 	return (__force void *)icsk->icsk_ulp_data;

include/net/inet_connection_sock.h

@@ -147,10 +147,7 @@ struct inet_connection_sock {
 #define ICSK_TIME_LOSS_PROBE	5	/* Tail loss probe timer */
 #define ICSK_TIME_REO_TIMEOUT	6	/* Reordering timer */
 
-static inline struct inet_connection_sock *inet_csk(const struct sock *sk)
-{
-	return (struct inet_connection_sock *)sk;
-}
+#define inet_csk(ptr) container_of_const(ptr, struct inet_connection_sock, icsk_inet.sk)
 
 static inline void *inet_csk_ca(const struct sock *sk)
 {

include/net/tcp.h

@@ -742,7 +742,7 @@ int tcp_mtu_to_mss(struct sock *sk, int pmtu);
 int tcp_mss_to_mtu(struct sock *sk, int mss);
 void tcp_mtup_init(struct sock *sk);
 
-static inline void tcp_bound_rto(const struct sock *sk)
+static inline void tcp_bound_rto(struct sock *sk)
 {
 	if (inet_csk(sk)->icsk_rto > TCP_RTO_MAX)
 		inet_csk(sk)->icsk_rto = TCP_RTO_MAX;

include/net/tls.h

@@ -361,7 +361,7 @@ static inline bool tls_is_skb_tx_device_offloaded(const struct sk_buff *skb)
 
 static inline struct tls_context *tls_get_ctx(const struct sock *sk)
 {
-	struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 	/* Use RCU on icsk_ulp_data only for sock diag code,
 	 * TLS data path doesn't need rcu_dereference().

net/ipv4/tcp_input.c

@@ -6999,7 +6999,7 @@ EXPORT_SYMBOL(inet_reqsk_alloc);
 /*
  * Return true if a syncookie should be sent
  */
-static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
+static bool tcp_syn_flood_action(struct sock *sk, const char *proto)
 {
 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
 	const char *msg = "Dropping request";

net/ipv4/tcp_timer.c

@@ -25,7 +25,7 @@
 
 static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
 {
-	struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 	const struct tcp_sock *tp = tcp_sk(sk);
 	u32 elapsed, user_timeout;
 	s32 remaining;
@@ -47,7 +47,7 @@ static u32 tcp_clamp_rto_to_user_timeout(const struct sock *sk)
 
 u32 tcp_clamp_probe0_to_user_timeout(const struct sock *sk, u32 when)
 {
-	struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 	u32 remaining, user_timeout;
 	s32 elapsed;
 

net/mptcp/protocol.h

@@ -558,7 +558,7 @@ struct mptcp_subflow_context {
 static inline struct mptcp_subflow_context *
 mptcp_subflow_ctx(const struct sock *sk)
 {
-	struct inet_connection_sock *icsk = inet_csk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
 
 	/* Use RCU on icsk_ulp_data only for sock diag code */
 	return (__force struct mptcp_subflow_context *)icsk->icsk_ulp_data;