gre: Drop ip_route_output_gre().

We already have enough variants of ip_route_output*() functions. We
don't need a GRE specific one in the generic route.h header file.

Furthermore, ip_route_output_gre() is only used once, in ipgre_open(),
where it can be easily replaced by a simple call to
ip_route_output_key().

While there, and for clarity, explicitly set .flowi4_scope to
RT_SCOPE_UNIVERSE instead of relying on the implicit zero
initialisation.

Signed-off-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Link: https://patch.msgid.link/ab7cba47b8558cd4bfe2dc843c38b622a95ee48e.1734527729.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

include/net/route.h

@@ -185,20 +185,6 @@ static inline struct rtable *ip_route_output_ports(struct net *net, struct flowi
 	return ip_route_output_flow(net, fl4, sk);
 }
 
-static inline struct rtable *ip_route_output_gre(struct net *net, struct flowi4 *fl4,
-						 __be32 daddr, __be32 saddr,
-						 __be32 gre_key, __u8 tos, int oif)
-{
-	memset(fl4, 0, sizeof(*fl4));
-	fl4->flowi4_oif = oif;
-	fl4->daddr = daddr;
-	fl4->saddr = saddr;
-	fl4->flowi4_tos = tos;
-	fl4->flowi4_proto = IPPROTO_GRE;
-	fl4->fl4_gre_key = gre_key;
-	return ip_route_output_key(net, fl4);
-}
-
 enum skb_drop_reason
 ip_mc_validate_source(struct sk_buff *skb, __be32 daddr, __be32 saddr,
 		      dscp_t dscp, struct net_device *dev,

net/ipv4/ip_gre.c

@@ -924,15 +924,18 @@ static int ipgre_open(struct net_device *dev)
 	struct ip_tunnel *t = netdev_priv(dev);
 
 	if (ipv4_is_multicast(t->parms.iph.daddr)) {
-		struct flowi4 fl4;
+		struct flowi4 fl4 = {
+			.flowi4_oif = t->parms.link,
+			.flowi4_tos = t->parms.iph.tos & INET_DSCP_MASK,
+			.flowi4_scope = RT_SCOPE_UNIVERSE,
+			.flowi4_proto = IPPROTO_GRE,
+			.saddr = t->parms.iph.saddr,
+			.daddr = t->parms.iph.daddr,
+			.fl4_gre_key = t->parms.o_key,
+		};
 		struct rtable *rt;
 
-		rt = ip_route_output_gre(t->net, &fl4,
-					 t->parms.iph.daddr,
-					 t->parms.iph.saddr,
-					 t->parms.o_key,
-					 t->parms.iph.tos & INET_DSCP_MASK,
-					 t->parms.link);
+		rt = ip_route_output_key(t->net, &fl4);
 		if (IS_ERR(rt))
 			return -EADDRNOTAVAIL;
 		dev = rt->dst.dev;