Improve mechanism for using loopback interface as BVI for BDs

When loopback interface is configured as BVI, instead of changing its
output node from loopN-output to l2-input, the loopN-output node is now
kept while its next tx node is changed from ethernet-input to l2-input.
The packet setup previously done in bvi_to_l2 as part of l2-input is now
performed in the loop output node.

This change adds an extra node in the BVI output path but provides the
following improvements:
1. IP address/route created on loopback prior to it being configured as
   BVI will still work properly. The requirement to (re)configure IP/route
   on loopback after it is configured as BVI is removed.
2. The output stats for loopback interfaces are always provided irrespective
   of their BVI configuration.
3. The loopback-BVI output stats can be batch updated outside the packet
   loop in output node, instead of per packet update in l2-input node,
   making l2-input node more efficient for BVI packets.
4. Restore original node property as implemented in node.c function
   vlib_node_add_next_with_slot() where next node indices stored in next
   slots of each node will remain unique.
5. Packet trace for BVI output includes loopN output node which provides
   useful packet data.

Change-Id: I7f5bc72ef953a367363a179088210596881f9e73
Signed-off-by: John Lo <loj@cisco.com>

1 files changed, 5 insertions, 4 deletions

diff --git a/vlib/vlib/node.c b/vlib/vlib/node.c
index 1df786f0c89..7378701ab4d 100644
--- a/vlib/vlib/node.c
+++ b/vlib/vlib/node.c
@@ -177,9 +177,10 @@ vlib_node_add_next_with_slot (vlib_main_t * vm,
 
   if ((p = hash_get (node->next_slot_by_node, next_node_index)))
     {
-      /* Next already exists: use it if slot not specified or the same. */
-      if ((slot == ~0) || (slot == p[0]))
-	  return p[0];
+      /* Next already exists: slot must match. */
+      if (slot != ~0)
+	ASSERT (slot == p[0]);
+      return p[0];
     }
 
   if (slot == ~0)
@@ -189,7 +190,7 @@ vlib_node_add_next_with_slot (vlib_main_t * vm,
   vec_validate (node->n_vectors_by_next_node, slot);
 
   node->next_nodes[slot] = next_node_index;
-  if (!p) hash_set (node->next_slot_by_node, next_node_index, slot);
+  hash_set (node->next_slot_by_node, next_node_index, slot);
 
   vlib_node_runtime_update (vm, node_index, slot);