net: Abstract default MTU metric calculation behind an accessor.

Like RTAX_ADVMSS, make the default calculation go through a dst_ops
method rather than caching the computation in the routing cache
entries.

Now dst metrics are pretty much left as-is when new entries are
created, thus optimizing metric sharing becomes a real possibility.

Signed-off-by: David S. Miller <davem@davemloft.net>

6 files changed, 60 insertions, 39 deletions

diff --git a/include/net/dst.h b/include/net/dst.h
index 03a1c3d52d80..93b0310317be 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -113,7 +113,8 @@ static inline u32
 dst_metric(const struct dst_entry *dst, const int metric)
 {
         WARN_ON_ONCE(metric == RTAX_HOPLIMIT ||
-                     metric == RTAX_ADVMSS);
+                     metric == RTAX_ADVMSS ||
+                     metric == RTAX_MTU);
         return dst_metric_raw(dst, metric);
 }
 
@@ -156,11 +157,11 @@ dst_feature(const struct dst_entry *dst, u32 feature)
 
 static inline u32 dst_mtu(const struct dst_entry *dst)
 {
-        u32 mtu = dst_metric(dst, RTAX_MTU);
-        /*
-         * Alexey put it here, so ask him about it :)
-         */
-        barrier();
+        u32 mtu = dst_metric_raw(dst, RTAX_MTU);
+
+        if (!mtu)
+                mtu = dst->ops->default_mtu(dst);
+
         return mtu;
 }
 
@@ -186,7 +187,7 @@ dst_allfrag(const struct dst_entry *dst)
 }
 
 static inline int
-dst_metric_locked(struct dst_entry *dst, int metric)
+dst_metric_locked(const struct dst_entry *dst, int metric)
 {
         return dst_metric(dst, RTAX_LOCK) & (1<<metric);
 }
diff --git a/include/net/dst_ops.h b/include/net/dst_ops.h
index 15fb7af08c42..21a320b8708e 100644
--- a/include/net/dst_ops.h
+++ b/include/net/dst_ops.h
@@ -17,6 +17,7 @@ struct dst_ops {
         int                     (*gc)(struct dst_ops *ops);
         struct dst_entry *      (*check)(struct dst_entry *, __u32 cookie);
         unsigned int            (*default_advmss)(const struct dst_entry *);
+        unsigned int            (*default_mtu)(const struct dst_entry *);
         void                    (*destroy)(struct dst_entry *);
         void                    (*ifdown)(struct dst_entry *,
                                           struct net_device *dev, int how);
diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index b8a5c0515be8..5e636365d33c 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -111,6 +111,7 @@ static unsigned long dn_rt_deadline;
 static int dn_dst_gc(struct dst_ops *ops);
 static struct dst_entry *dn_dst_check(struct dst_entry *, __u32);
 static unsigned int dn_dst_default_advmss(const struct dst_entry *dst);
+static unsigned int dn_dst_default_mtu(const struct dst_entry *dst);
 static struct dst_entry *dn_dst_negative_advice(struct dst_entry *);
 static void dn_dst_link_failure(struct sk_buff *);
 static void dn_dst_update_pmtu(struct dst_entry *dst, u32 mtu);
@@ -131,6 +132,7 @@ static struct dst_ops dn_dst_ops = {
         .gc =                   dn_dst_gc,
         .check =                dn_dst_check,
         .default_advmss =       dn_dst_default_advmss,
+        .default_mtu =          dn_dst_default_mtu,
         .negative_advice =      dn_dst_negative_advice,
         .link_failure =         dn_dst_link_failure,
         .update_pmtu =          dn_dst_update_pmtu,
@@ -803,6 +805,11 @@ static unsigned int dn_dst_default_advmss(const struct dst_entry *dst)
         return dn_mss_from_pmtu(dst->dev, dst_mtu(dst));
 }
 
+static unsigned int dn_dst_default_mtu(const struct dst_entry *dst)
+{
+        return dst->dev->mtu;
+}
+
 static int dn_rt_set_next_hop(struct dn_route *rt, struct dn_fib_res *res)
 {
         struct dn_fib_info *fi = res->fi;
@@ -825,8 +832,7 @@ static int dn_rt_set_next_hop(struct dn_route *rt, struct dn_fib_res *res)
                 rt->dst.neighbour = n;
         }
 
-        if (dst_metric(&rt->dst, RTAX_MTU) == 0 ||
-            dst_metric(&rt->dst, RTAX_MTU) > rt->dst.dev->mtu)
+        if (dst_metric(&rt->dst, RTAX_MTU) > rt->dst.dev->mtu)
                 dst_metric_set(&rt->dst, RTAX_MTU, rt->dst.dev->mtu);
         metric = dst_metric_raw(&rt->dst, RTAX_ADVMSS);
         if (metric) {
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 80997333db0c..ae520963540f 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -140,6 +140,7 @@ static unsigned long expires_ljiffies;
 
 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_default_mtu(const struct dst_entry *dst);
 static void              ipv4_dst_destroy(struct dst_entry *dst);
 static struct dst_entry *ipv4_negative_advice(struct dst_entry *dst);
 static void              ipv4_link_failure(struct sk_buff *skb);
@@ -157,6 +158,7 @@ static struct dst_ops ipv4_dst_ops = {
         .gc =                   rt_garbage_collect,
         .check =                ipv4_dst_check,
         .default_advmss =       ipv4_default_advmss,
+        .default_mtu =          ipv4_default_mtu,
         .destroy =              ipv4_dst_destroy,
         .ifdown =               ipv4_dst_ifdown,
         .negative_advice =      ipv4_negative_advice,
@@ -1812,6 +1814,23 @@ static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
         return advmss;
 }
 
+static unsigned int ipv4_default_mtu(const struct dst_entry *dst)
+{
+        unsigned int mtu = dst->dev->mtu;
+
+        if (unlikely(dst_metric_locked(dst, RTAX_MTU))) {
+                const struct rtable *rt = (const struct rtable *) dst;
+
+                if (rt->rt_gateway != rt->rt_dst && mtu > 576)
+                        mtu = 576;
+        }
+
+        if (mtu > IP_MAX_MTU)
+                mtu = IP_MAX_MTU;
+
+        return mtu;
+}
+
 static void rt_set_nexthop(struct rtable *rt, struct fib_result *res, u32 itag)
 {
         struct dst_entry *dst = &rt->dst;
@@ -1822,18 +1841,10 @@ static void rt_set_nexthop(struct rtable *rt, struct fib_result *res, u32 itag)
                     FIB_RES_NH(*res).nh_scope == RT_SCOPE_LINK)
                         rt->rt_gateway = FIB_RES_GW(*res);
                 dst_import_metrics(dst, fi->fib_metrics);
-                if (fi->fib_mtu == 0) {
-                        dst_metric_set(dst, RTAX_MTU, dst->dev->mtu);
-                        if (dst_metric_locked(dst, RTAX_MTU) &&
-                            rt->rt_gateway != rt->rt_dst &&
-                            dst->dev->mtu > 576)
-                                dst_metric_set(dst, RTAX_MTU, 576);
-                }
 #ifdef CONFIG_NET_CLS_ROUTE
                 dst->tclassid = FIB_RES_NH(*res).nh_tclassid;
 #endif
-        } else
-                dst_metric_set(dst, RTAX_MTU, dst->dev->mtu);
+        }
 
         if (dst_mtu(dst) > IP_MAX_MTU)
                 dst_metric_set(dst, RTAX_MTU, IP_MAX_MTU);
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index d9cb832be529..e7efb269a6e9 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -77,6 +77,7 @@
 static struct rt6_info * ip6_rt_copy(struct rt6_info *ort);
 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_default_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 *,
@@ -105,6 +106,7 @@ static struct dst_ops ip6_dst_ops_template = {
         .gc_thresh              =       1024,
         .check                  =       ip6_dst_check,
         .default_advmss         =       ip6_default_advmss,
+        .default_mtu            =       ip6_default_mtu,
         .destroy                =       ip6_dst_destroy,
         .ifdown                 =       ip6_dst_ifdown,
         .negative_advice        =       ip6_negative_advice,
@@ -937,8 +939,6 @@ static void ip6_rt_update_pmtu(struct dst_entry *dst, u32 mtu)
         }
 }
 
-static int ipv6_get_mtu(struct net_device *dev);
-
 static unsigned int ip6_default_advmss(const struct dst_entry *dst)
 {
         struct net_device *dev = dst->dev;
@@ -961,6 +961,20 @@ static unsigned int ip6_default_advmss(const struct dst_entry *dst)
         return mtu;
 }
 
+static unsigned int ip6_default_mtu(const struct dst_entry *dst)
+{
+        unsigned int mtu = IPV6_MIN_MTU;
+        struct inet6_dev *idev;
+
+        rcu_read_lock();
+        idev = __in6_dev_get(dst->dev);
+        if (idev)
+                mtu = idev->cnf.mtu6;
+        rcu_read_unlock();
+
+        return mtu;
+}
+
 static struct dst_entry *icmp6_dst_gc_list;
 static DEFINE_SPINLOCK(icmp6_dst_lock);
 
@@ -995,7 +1009,6 @@ struct dst_entry *icmp6_dst_alloc(struct net_device *dev,
         rt->rt6i_nexthop  = neigh;
         atomic_set(&rt->dst.__refcnt, 1);
         dst_metric_set(&rt->dst, RTAX_HOPLIMIT, 255);
-        dst_metric_set(&rt->dst, RTAX_MTU, ipv6_get_mtu(rt->rt6i_dev));
         rt->dst.output  = ip6_output;
 
 #if 0   /* there's no chance to use these for ndisc */
@@ -1094,19 +1107,6 @@ out:
    Remove it only when all the things will work!
  */
 
-static int ipv6_get_mtu(struct net_device *dev)
-{
-        int mtu = IPV6_MIN_MTU;
-        struct inet6_dev *idev;
-
-        rcu_read_lock();
-        idev = __in6_dev_get(dev);
-        if (idev)
-                mtu = idev->cnf.mtu6;
-        rcu_read_unlock();
-        return mtu;
-}
-
 int ip6_dst_hoplimit(struct dst_entry *dst)
 {
         int hoplimit = dst_metric_raw(dst, RTAX_HOPLIMIT);
@@ -1315,8 +1315,6 @@ install_route:
                 }
         }
 
-        if (!dst_mtu(&rt->dst))
-                dst_metric_set(&rt->dst, RTAX_MTU, ipv6_get_mtu(dev));
         rt->dst.dev = dev;
         rt->rt6i_idev = idev;
         rt->rt6i_table = table;
@@ -1541,8 +1539,6 @@ void rt6_redirect(struct in6_addr *dest, struct in6_addr *src,
 
         ipv6_addr_copy(&nrt->rt6i_gateway, (struct in6_addr*)neigh->primary_key);
         nrt->rt6i_nexthop = neigh_clone(neigh);
-        /* Reset pmtu, it may be better */
-        dst_metric_set(&nrt->dst, RTAX_MTU, ipv6_get_mtu(neigh->dev));
 
         if (ip6_ins_rt(nrt))
                 goto out;
@@ -1971,7 +1967,6 @@ struct rt6_info *addrconf_dst_alloc(struct inet6_dev *idev,
         rt->dst.output = ip6_output;
         rt->rt6i_dev = net->loopback_dev;
         rt->rt6i_idev = idev;
-        dst_metric_set(&rt->dst, RTAX_MTU, ipv6_get_mtu(rt->rt6i_dev));
         dst_metric_set(&rt->dst, RTAX_HOPLIMIT, -1);
         rt->dst.obsolete = -1;
 
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 36936c8ae961..8b3ef404c794 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -2366,6 +2366,11 @@ static unsigned int xfrm_default_advmss(const struct dst_entry *dst)
         return dst_metric_advmss(dst->path);
 }
 
+static unsigned int xfrm_default_mtu(const struct dst_entry *dst)
+{
+        return dst_mtu(dst->path);
+}
+
 int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
 {
         struct net *net;
@@ -2385,6 +2390,8 @@ int xfrm_policy_register_afinfo(struct xfrm_policy_afinfo *afinfo)
                         dst_ops->check = xfrm_dst_check;
                 if (likely(dst_ops->default_advmss == NULL))
                         dst_ops->default_advmss = xfrm_default_advmss;
+                if (likely(dst_ops->default_mtu == NULL))
+                        dst_ops->default_mtu = xfrm_default_mtu;
                 if (likely(dst_ops->negative_advice == NULL))
                         dst_ops->negative_advice = xfrm_negative_advice;
                 if (likely(dst_ops->link_failure == NULL))