net: Move mtu handling down to the protocol depended handlers

We move all mtu handling from dst_mtu() down to the protocol
layer. So each protocol can implement the mtu handling in
a different manner.

Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 2 deletions

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index f1ac3efc5524..11d1b2080a16 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1816,7 +1816,12 @@ static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
 
 static unsigned int ipv4_mtu(const struct dst_entry *dst)
 {
-        unsigned int mtu = dst->dev->mtu;
+        unsigned int mtu = dst_metric_raw(dst, RTAX_MTU);
+
+        if (mtu)
+                return mtu;
+
+        mtu = dst->dev->mtu;
 
         if (unlikely(dst_metric_locked(dst, RTAX_MTU))) {
                 const struct rtable *rt = (const struct rtable *) dst;
@@ -2757,7 +2762,9 @@ static struct dst_entry *ipv4_blackhole_dst_check(struct dst_entry *dst, u32 coo
 
 static unsigned int ipv4_blackhole_mtu(const struct dst_entry *dst)
 {
-        return dst->dev->mtu;
+        unsigned int mtu = dst_metric_raw(dst, RTAX_MTU);
+
+        return mtu ? : dst->dev->mtu;
 }
 
 static void ipv4_rt_blackhole_update_pmtu(struct dst_entry *dst, u32 mtu)