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>

2 files changed, 9 insertions, 7 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);