FIB2.0: Adjacency complete pull model (VPP-487)

Change the adjacency completion model to pull not push.

A complete adjacency has a rewirte string, an incomplete one does not. the re-write string for a peer comes either from a discovery protocol (i.e. ARP/ND) or can be directly derived from the link type (i.e. GRE tunnels). Which method it is, is interface type specific.
For each packet type sent on a link to a peer there is a corresponding adjacency. For example, if there is a peer 10.0.0.1 on Eth0 and we need to send to it IPv4 and MPLS packets, there will be two adjacencies; one for the IPv4 and one for the MPLS packets. The adjacencies are thus distinguished by the packets the carry, this is known as the adjacency's 'link-type'. It is not an L3 packet type, since the adjacency can have a link type of Ethernet (for L2 over GRE).
The discovery protocols are not aware of all the link types required - only the FIB is. the FIB will create adjacencies as and when they are required, and it is thus then desirable to 'pull' from the discovery protocol the re-write required. The alternative (that we have now) is that the discovery protocol pushes (i.e. creates) adjacencies for each link type - this creates more adjacencies than we need.
To pull, FIB now requests from the interface-type to 'complete' the adjacency. The interface can then delegate to the discovery protocol (on ethernet links) or directly build the re-write (i.e on GRE).

Change-Id: I61451789ae03f26b1012d8d6524007b769b6c6ee
Signed-off-by: Neale Ranns <nranns@cisco.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/vnet/vnet/ip/ip4_forward.c b/vnet/vnet/ip/ip4_forward.c
index 21973453af7..b0390b8a44a 100644
--- a/vnet/vnet/ip/ip4_forward.c
+++ b/vnet/vnet/ip/ip4_forward.c
@@ -1118,7 +1118,7 @@ static u8 * format_ip4_rewrite_trace (u8 * s, va_list * args)
 
   s = format (s, "tx_sw_if_index %d dpo-idx %d : %U flow hash: 0x%08x",
               t->fib_index, t->dpo_index, format_ip_adjacency,
-              vnm, t->dpo_index, FORMAT_IP_ADJACENCY_NONE,
+              t->dpo_index, FORMAT_IP_ADJACENCY_NONE,
 	      t->flow_hash);
   s = format (s, "\n%U%U",
               format_white_space, indent,
@@ -1890,6 +1890,13 @@ ip4_arp_inline (vlib_main_t * vm,
 
 	  p0->error = node->errors[drop0 ? IP4_ARP_ERROR_DROP : IP4_ARP_ERROR_REQUEST_SENT];
 
+	  /*
+	   * the adj has been updated to a rewrite but the node the DPO that got
+	   * us here hasn't - yet. no big deal. we'll drop while we wait.
+	   */
+	  if (IP_LOOKUP_NEXT_REWRITE == adj0->lookup_next_index)
+	    continue;
+
 	  if (drop0)
 	    continue;