core: add stat to track unresolved discards in neighbor cache

in __neigh_event_send, if we have a neighbour entry which is in
NUD_INCOMPLETE state, we enqueue any outbound frames to that neighbour
to the neighbours arp_queue, which is default capped to a length of 3
skbs.  If that queue exceeds its set length, it will drop an skb on
the queue to enqueue the newly arrived skb.  This results in a drop
for which we have no statistics incremented.  This patch adds an
unresolved_discards stat to /proc/net/stat/ndisc_cache to track these
lost frames.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 65f01f71b3f..f62c8af85d3 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -930,6 +930,7 @@ int __neigh_event_send(struct neighbour *neigh, struct sk_buff *skb)
                                 buff = neigh->arp_queue.next;
                                 __skb_unlink(buff, &neigh->arp_queue);
                                 kfree_skb(buff);
+                                NEIGH_CACHE_STAT_INC(neigh->tbl, unres_discards);
                         }
                         __skb_queue_tail(&neigh->arp_queue, skb);
                 }
@@ -2462,12 +2463,12 @@ static int neigh_stat_seq_show(struct seq_file *seq, void *v)
         struct neigh_statistics *st = v;
 
         if (v == SEQ_START_TOKEN) {
-                seq_printf(seq, "entries  allocs destroys hash_grows  lookups hits  res_failed  rcv_probes_mcast rcv_probes_ucast  periodic_gc_runs forced_gc_runs\n");
+                seq_printf(seq, "entries  allocs destroys hash_grows  lookups hits  res_failed  rcv_probes_mcast rcv_probes_ucast  periodic_gc_runs forced_gc_runs unresolved_discards\n");
                 return 0;
         }
 
         seq_printf(seq, "%08x  %08lx %08lx %08lx  %08lx %08lx  %08lx  "
-                        "%08lx %08lx  %08lx %08lx\n",
+                        "%08lx %08lx  %08lx %08lx %08lx\n",
                    atomic_read(&tbl->entries),
 
                    st->allocs,
@@ -2483,7 +2484,8 @@ static int neigh_stat_seq_show(struct seq_file *seq, void *v)
                    st->rcv_probes_ucast,
 
                    st->periodic_gc_runs,
-                   st->forced_gc_runs
+                   st->forced_gc_runs,
+                   st->unres_discards
                    );
 
         return 0;