ipv4: Add FLOWI_FLAG_KNOWN_NH

Add flag to request that output route should be
returned with known rt_gateway, in case we want to use
it as nexthop for neighbour resolving.

	The returned route can be cached as follows:

- in NH exception: because the cached routes are not shared
	with other destinations
- in FIB NH: when using gateway because all destinations for
	NH share same gateway

	As last option, to return rt_gateway!=0 we have to
set DST_NOCACHE.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 17 insertions, 4 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 3a116cb0991a..1a0da8dc8180 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1762,6 +1762,7 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
         struct in_device *in_dev;
         u16 type = res->type;
         struct rtable *rth;
+        bool do_cache;
 
         in_dev = __in_dev_get_rcu(dev_out);
         if (!in_dev)
@@ -1798,24 +1799,36 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
         }
 
         fnhe = NULL;
+        do_cache = fi != NULL;
         if (fi) {
                 struct rtable __rcu **prth;
+                struct fib_nh *nh = &FIB_RES_NH(*res);
 
-                fnhe = find_exception(&FIB_RES_NH(*res), fl4->daddr);
+                fnhe = find_exception(nh, fl4->daddr);
                 if (fnhe)
                         prth = &fnhe->fnhe_rth;
-                else
-                        prth = __this_cpu_ptr(FIB_RES_NH(*res).nh_pcpu_rth_output);
+                else {
+                        if (unlikely(fl4->flowi4_flags &
+                                     FLOWI_FLAG_KNOWN_NH &&
+                                     !(nh->nh_gw &&
+                                       nh->nh_scope == RT_SCOPE_LINK))) {
+                                do_cache = false;
+                                goto add;
+                        }
+                        prth = __this_cpu_ptr(nh->nh_pcpu_rth_output);
+                }
                 rth = rcu_dereference(*prth);
                 if (rt_cache_valid(rth)) {
                         dst_hold(&rth->dst);
                         return rth;
                 }
         }
+
+add:
         rth = rt_dst_alloc(dev_out,
                            IN_DEV_CONF_GET(in_dev, NOPOLICY),
                            IN_DEV_CONF_GET(in_dev, NOXFRM),
-                           fi);
+                           do_cache);
         if (!rth)
                 return ERR_PTR(-ENOBUFS);