net: use indirect call helpers for dst_mtu

This patch avoids the indirect call for the common case:
ip6_mtu and ipv4_mtu
Signed-off-by: Brian Vazquez <brianvv@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/dst.h

@@ -194,9 +194,11 @@ dst_feature(const struct dst_entry *dst, u32 feature)
 	return dst_metric(dst, RTAX_FEATURES) & feature;
 }
 
+INDIRECT_CALLABLE_DECLARE(unsigned int ip6_mtu(const struct dst_entry *));
+INDIRECT_CALLABLE_DECLARE(unsigned int ipv4_mtu(const struct dst_entry *));
 static inline u32 dst_mtu(const struct dst_entry *dst)
 {
-	return dst->ops->mtu(dst);
+	return INDIRECT_CALL_INET(dst->ops->mtu, ip6_mtu, ipv4_mtu, dst);
 }
 
 /* RTT metrics are stored in milliseconds for user ABI, but used as jiffies */

net/ipv4/route.c

@@ -135,7 +135,8 @@ static int ip_rt_gc_timeout __read_mostly	= RT_GC_TIMEOUT;
 
 static struct dst_entry *ipv4_dst_check(struct dst_entry *dst, u32 cookie);
 static unsigned int	 ipv4_default_advmss(const struct dst_entry *dst);
-static unsigned int	 ipv4_mtu(const struct dst_entry *dst);
+INDIRECT_CALLABLE_SCOPE
+unsigned int		ipv4_mtu(const struct dst_entry *dst);
 static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst);
 static void		 ipv4_link_failure(struct sk_buff *skb);
 static void		 ip_rt_update_pmtu(struct dst_entry *dst, struct sock *sk,
@@ -1311,7 +1312,7 @@ static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
 	return min(advmss, IPV4_MAX_PMTU - header_size);
 }
 
-static unsigned int ipv4_mtu(const struct dst_entry *dst)
+INDIRECT_CALLABLE_SCOPE unsigned int ipv4_mtu(const struct dst_entry *dst)
 {
 	const struct rtable *rt = (const struct rtable *)dst;
 	unsigned int mtu = rt->rt_pmtu;
@@ -1333,6 +1334,7 @@ static unsigned int ipv4_mtu(const struct dst_entry *dst)
 
 	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
 }
+EXPORT_SYMBOL(ipv4_mtu);
 
 static void ip_del_fnhe(struct fib_nh_common *nhc, __be32 daddr)
 {

net/ipv6/route.c

@@ -83,7 +83,8 @@ enum rt6_nud_state {
 
 static struct dst_entry	*ip6_dst_check(struct dst_entry *dst, u32 cookie);
 static unsigned int	 ip6_default_advmss(const struct dst_entry *dst);
-static unsigned int	 ip6_mtu(const struct dst_entry *dst);
+INDIRECT_CALLABLE_SCOPE
+unsigned int		ip6_mtu(const struct dst_entry *dst);
 static struct dst_entry *ip6_negative_advice(struct dst_entry *);
 static void		ip6_dst_destroy(struct dst_entry *);
 static void		ip6_dst_ifdown(struct dst_entry *,
@@ -3089,7 +3090,7 @@ static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 	return mtu;
 }
 
-static unsigned int ip6_mtu(const struct dst_entry *dst)
+INDIRECT_CALLABLE_SCOPE unsigned int ip6_mtu(const struct dst_entry *dst)
 {
 	struct inet6_dev *idev;
 	unsigned int mtu;
@@ -3111,6 +3112,7 @@ static unsigned int ip6_mtu(const struct dst_entry *dst)
 
 	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
 }
+EXPORT_SYMBOL(ip6_mtu);
 
 /* MTU selection:
  * 1. mtu on route is locked - use it