[PATCH 6.6.y 2/5] inet: add dst4_mtu() and dst6_mtu() helpers

[Sasha Levin <sashal@kernel.org>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 8776c4ef3ab22b95f55713f00a7a576e6402507d ]

With CONFIG_MITIGATION_RETPOLINE=y dst_mtu() is a bit fat,
because it is generic.

Indeed, clang does not always inline it.

Add dst4_mtu() and dst6_mtu() helpers for callers that
expect either ipv4_mtu() or ip6_mtu() to be called.

These helpers are always inlined.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260130210303.3888261-6-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Stable-dep-of: 870a9e42ecc6 ("tcp: clamp route advmss to TCP_MIN_MSS")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 include/net/dst.h       | 6 ++++++
 include/net/ip6_route.h | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/include/net/dst.h b/include/net/dst.h
index 55d1be268d243..e1c4a806597da 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -216,6 +216,12 @@ static inline u32 dst_mtu(const struct dst_entry *dst)
 	return INDIRECT_CALL_INET(dst->ops->mtu, ip6_mtu, ipv4_mtu, dst);
 }
 
+/* Variant of dst_mtu() for IPv4 users. */
+static inline u32 dst4_mtu(const struct dst_entry *dst)
+{
+	return INDIRECT_CALL_1(dst->ops->mtu, ipv4_mtu, dst);
+}
+
 /* RTT metrics are stored in milliseconds for user ABI, but used as jiffies */
 static inline unsigned long dst_metric_rtt(const struct dst_entry *dst, int metric)
 {
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 392232fcd703c..55c9ccfa0bcb8 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -266,6 +266,12 @@ static inline bool ipv6_anycast_destination(const struct dst_entry *dst,
 int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
 		 int (*output)(struct net *, struct sock *, struct sk_buff *));
 
+/* Variant of dst_mtu() for IPv6 users */
+static inline u32 dst6_mtu(const struct dst_entry *dst)
+{
+	return INDIRECT_CALL_1(dst->ops->mtu, ip6_mtu, dst);
+}
+
 static inline unsigned int ip6_skb_dst_mtu(const struct sk_buff *skb)
 {
 	const struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
-- 
2.53.0