ila: Cache a route to translated address

Add a dst_cache to ila_lwt structure. This holds a cached route for the
translated address. In ila_output we now perform a route lookup after
translation and if possible (destination in original route is full 128
bits) we set the dst_cache. Subsequent calls to ila_output can then use
the cache to avoid the route lookup.

This eliminates the need to set the gateway on ILA routes as previously
was being done. Now we can do something like:

./ip route add 3333::2000:0:0:2/128 encap ila 2222:0:0:2 \
    csum-mode neutral-map dev eth0  ## No via needed!

Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ila/ila_lwt.c

@@ -6,29 +6,80 @@
 #include <linux/socket.h>
 #include <linux/types.h>
 #include <net/checksum.h>
+#include <net/dst_cache.h>
 #include <net/ip.h>
 #include <net/ip6_fib.h>
+#include <net/ip6_route.h>
 #include <net/lwtunnel.h>
 #include <net/protocol.h>
 #include <uapi/linux/ila.h>
 #include "ila.h"
 
+struct ila_lwt {
+	struct ila_params p;
+	struct dst_cache dst_cache;
+	u32 connected : 1;
+};
+
+static inline struct ila_lwt *ila_lwt_lwtunnel(
+	struct lwtunnel_state *lwt)
+{
+	return (struct ila_lwt *)lwt->data;
+}
+
 static inline struct ila_params *ila_params_lwtunnel(
-	struct lwtunnel_state *lwstate)
+	struct lwtunnel_state *lwt)
 {
-	return (struct ila_params *)lwstate->data;
+	return &ila_lwt_lwtunnel(lwt)->p;
 }
 
 static int ila_output(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
-	struct dst_entry *dst = skb_dst(skb);
+	struct dst_entry *orig_dst = skb_dst(skb);
+	struct ila_lwt *ilwt = ila_lwt_lwtunnel(orig_dst->lwtstate);
+	struct dst_entry *dst;
+	int err = -EINVAL;
 
 	if (skb->protocol != htons(ETH_P_IPV6))
 		goto drop;
 
-	ila_update_ipv6_locator(skb, ila_params_lwtunnel(dst->lwtstate), true);
+	ila_update_ipv6_locator(skb, ila_params_lwtunnel(orig_dst->lwtstate),
+				true);
+
+	dst = dst_cache_get(&ilwt->dst_cache);
+	if (unlikely(!dst)) {
+		struct ipv6hdr *ip6h = ipv6_hdr(skb);
+		struct flowi6 fl6;
+
+		/* Lookup a route for the new destination. Take into
+		 * account that the base route may already have a gateway.
+		 */
+
+		memset(&fl6, 0, sizeof(fl6));
+		fl6.flowi6_oif = orig_dst->dev->ifindex;
+		fl6.flowi6_iif = LOOPBACK_IFINDEX;
+		fl6.daddr = *rt6_nexthop((struct rt6_info *)orig_dst,
+					 &ip6h->daddr);
+
+		dst = ip6_route_output(net, NULL, &fl6);
+		if (dst->error) {
+			err = -EHOSTUNREACH;
+			dst_release(dst);
+			goto drop;
+		}
+
+		dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0);
+		if (IS_ERR(dst)) {
+			err = PTR_ERR(dst);
+			goto drop;
+		}
+
+		if (ilwt->connected)
+			dst_cache_set_ip6(&ilwt->dst_cache, dst, &fl6.saddr);
+	}
 
-	return dst->lwtstate->orig_output(net, sk, skb);
+	skb_dst_set(skb, dst);
+	return dst_output(net, sk, skb);
 
 drop:
 	kfree_skb(skb);
@@ -60,6 +111,7 @@ static int ila_build_state(struct net_device *dev, struct nlattr *nla,
 			   unsigned int family, const void *cfg,
 			   struct lwtunnel_state **ts)
 {
+	struct ila_lwt *ilwt;
 	struct ila_params *p;
 	struct nlattr *tb[ILA_ATTR_MAX + 1];
 	size_t encap_len = sizeof(*p);
@@ -71,7 +123,7 @@ static int ila_build_state(struct net_device *dev, struct nlattr *nla,
 	if (family != AF_INET6)
 		return -EINVAL;
 
-	if (cfg6->fc_dst_len < sizeof(struct ila_locator) + 1) {
+	if (cfg6->fc_dst_len < 8 * sizeof(struct ila_locator) + 3) {
 		/* Need to have full locator and at least type field
 		 * included in destination
 		 */
@@ -99,6 +151,13 @@ static int ila_build_state(struct net_device *dev, struct nlattr *nla,
 	if (!newts)
 		return -ENOMEM;
 
+	ilwt = ila_lwt_lwtunnel(newts);
+	ret = dst_cache_init(&ilwt->dst_cache, GFP_ATOMIC);
+	if (ret) {
+		kfree(newts);
+		return ret;
+	}
+
 	newts->len = encap_len;
 	p = ila_params_lwtunnel(newts);
 
@@ -120,11 +179,19 @@ static int ila_build_state(struct net_device *dev, struct nlattr *nla,
 	newts->flags |= LWTUNNEL_STATE_OUTPUT_REDIRECT |
 			LWTUNNEL_STATE_INPUT_REDIRECT;
 
+	if (cfg6->fc_dst_len == 8 * sizeof(struct in6_addr))
+		ilwt->connected = 1;
+
 	*ts = newts;
 
 	return 0;
 }
 
+static void ila_destroy_state(struct lwtunnel_state *lwt)
+{
+	dst_cache_destroy(&ila_lwt_lwtunnel(lwt)->dst_cache);
+}
+
 static int ila_fill_encap_info(struct sk_buff *skb,
 			       struct lwtunnel_state *lwtstate)
 {
@@ -159,6 +226,7 @@ static int ila_encap_cmp(struct lwtunnel_state *a, struct lwtunnel_state *b)
 
 static const struct lwtunnel_encap_ops ila_encap_ops = {
 	.build_state = ila_build_state,
+	.destroy_state = ila_destroy_state,
 	.output = ila_output,
 	.input = ila_input,
 	.fill_encap = ila_fill_encap_info,