net: Abstract default ADVMSS behind an accessor.

Make all RTAX_ADVMSS metric accesses go through a new helper function,
dst_metric_advmss().

Leave the actual default metric as "zero" in the real metric slot,
and compute the actual default value dynamically via a new dst_ops
AF specific callback.

For stacked IPSEC routes, we use the advmss of the path which
preserves existing behavior.

Unlike ipv4/ipv6, DecNET ties the advmss to the mtu and thus updates
advmss on pmtu updates.  This inconsistency in advmss handling
results in more raw metric accesses than I wish we ended up with.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/net/decnet/af_decnet.c b/net/decnet/af_decnet.c
index 0065e7e14af4..2af15b15d1fa 100644
--- a/net/decnet/af_decnet.c
+++ b/net/decnet/af_decnet.c
@@ -829,7 +829,7 @@ static int dn_confirm_accept(struct sock *sk, long *timeo, gfp_t allocation)
                 return -EINVAL;
 
         scp->state = DN_CC;
-        scp->segsize_loc = dst_metric(__sk_dst_get(sk), RTAX_ADVMSS);
+        scp->segsize_loc = dst_metric_advmss(__sk_dst_get(sk));
         dn_send_conn_conf(sk, allocation);
 
         prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
@@ -958,7 +958,7 @@ static int __dn_connect(struct sock *sk, struct sockaddr_dn *addr, int addrlen,
         sk->sk_route_caps = sk->sk_dst_cache->dev->features;
         sock->state = SS_CONNECTING;
         scp->state = DN_CI;
-        scp->segsize_loc = dst_metric(sk->sk_dst_cache, RTAX_ADVMSS);
+        scp->segsize_loc = dst_metric_advmss(sk->sk_dst_cache);
 
         dn_nsp_send_conninit(sk, NSP_CI);
         err = -EINPROGRESS;