bpf, dst: add and use dst_tclassid helper

We can just add a small helper dst_tclassid() for retrieving the
dst->tclassid value. It makes the code a bit better in that we can
get rid of the ifdef from filter.c by moving this into the header.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dst.h

@@ -398,6 +398,18 @@ static inline void skb_tunnel_rx(struct sk_buff *skb, struct net_device *dev,
 	__skb_tunnel_rx(skb, dev, net);
 }
 
+static inline u32 dst_tclassid(const struct sk_buff *skb)
+{
+#ifdef CONFIG_IP_ROUTE_CLASSID
+	const struct dst_entry *dst;
+
+	dst = skb_dst(skb);
+	if (dst)
+		return dst->tclassid;
+#endif
+	return 0;
+}
+
 int dst_discard_out(struct net *net, struct sock *sk, struct sk_buff *skb);
 static inline int dst_discard(struct sk_buff *skb)
 {

net/core/filter.c

@@ -1682,14 +1682,7 @@ static const struct bpf_func_proto bpf_get_cgroup_classid_proto = {
 
 static u64 bpf_get_route_realm(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
 {
-#ifdef CONFIG_IP_ROUTE_CLASSID
-	const struct dst_entry *dst;
-
-	dst = skb_dst((struct sk_buff *) (unsigned long) r1);
-	if (dst)
-		return dst->tclassid;
-#endif
-	return 0;
+	return dst_tclassid((struct sk_buff *) (unsigned long) r1);
 }
 
 static const struct bpf_func_proto bpf_get_route_realm_proto = {