vlib: introduce lazy next node initialization

This change allow a node registration A to name a next node B that does not
exist yet at registration time. When node B is effectively created,
vlib_node_main_lazy_next_update need to be called so that the vlib graph
is updated accordingly. To enable this behavior, node A needs to bear
the new VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES.

Change-Id: I561d3a0de19a0b7bd1045760a2ba8e27d27caa9a
Type: improvement
Signed-off-by: Mohammed Hawari <mohammed@hawari.fr>

src/vlib/main.c

@@ -569,6 +569,9 @@ vlib_node_sync_stats (vlib_main_t * vm, vlib_node_t * n)
     uword i;
     for (i = 0; i < rt->n_next_nodes; i++)
       {
+	if (n->flags & VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES &&
+	    n->next_nodes[i] == VLIB_INVALID_NODE_INDEX)
+	  continue;
 	nf = vlib_node_runtime_get_next_frame (vm, rt, i);
 	vec_elt (n->n_vectors_by_next_node, i) +=
 	  nf->vectors_since_last_overflow;

src/vlib/node.c

@@ -805,7 +805,8 @@ vlib_node_main_init (vlib_main_t * vm)
 	  if (!a)
 	    continue;
 
-	  if (~0 == vlib_node_add_named_next_with_slot (vm, n->index, a, i))
+	  if (~0 == vlib_node_add_named_next_with_slot (vm, n->index, a, i) &&
+	      !(n->flags & VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES))
 	    {
 	      error = clib_error_create
 		("node `%v' refers to unknown node `%s'", n->name, a);
@@ -813,7 +814,8 @@ vlib_node_main_init (vlib_main_t * vm)
 	    }
 	}
 
-      vec_free (n->next_node_names);
+      if (!(n->flags & VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES))
+	vec_free (n->next_node_names);
     }
 
   /* Set previous node pointers. */
@@ -851,14 +853,18 @@ vlib_node_main_init (vlib_main_t * vm)
 
       for (i = 0; i < vec_len (n->next_nodes); i++)
 	{
-	  next = vlib_get_node (vm, n->next_nodes[i]);
+	    if (n->flags & VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES &&
+		n->next_nodes[i] >= vec_len (nm->nodes))
+	      continue;
 
-	  /* Validate node runtime indices are correctly initialized. */
-	  ASSERT (nf[i].node_runtime_index == next->runtime_index);
+	    next = vlib_get_node (vm, n->next_nodes[i]);
 
-	  nf[i].flags = 0;
-	  if (next->flags & VLIB_NODE_FLAG_FRAME_NO_FREE_AFTER_DISPATCH)
-	    nf[i].flags |= VLIB_FRAME_NO_FREE_AFTER_DISPATCH;
+	    /* Validate node runtime indices are correctly initialized. */
+	    ASSERT (nf[i].node_runtime_index == next->runtime_index);
+
+	    nf[i].flags = 0;
+	    if (next->flags & VLIB_NODE_FLAG_FRAME_NO_FREE_AFTER_DISPATCH)
+	      nf[i].flags |= VLIB_FRAME_NO_FREE_AFTER_DISPATCH;
 	}
     }
   }
@@ -927,6 +933,33 @@ vlib_node_set_march_variant (vlib_main_t *vm, u32 node_index,
     }
   return -1;
 }
+
+clib_error_t *
+vlib_node_main_lazy_next_update (vlib_main_t *vm)
+{
+  vlib_node_main_t *nm = &vm->node_main;
+  uword ni;
+  vlib_node_t *n;
+  for (ni = 0; ni < vec_len (nm->nodes); ni++)
+    {
+      uword nni;
+      n = vec_elt (nm->nodes, ni);
+
+      if (!(n->flags & VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES))
+	continue;
+
+      for (nni = 0; nni < vec_len (n->next_node_names); nni++)
+	{
+	  char *a = n->next_node_names[nni];
+
+	  if (!a)
+	    continue;
+
+	  vlib_node_add_named_next_with_slot (vm, n->index, a, nni);
+	}
+    }
+  return 0;
+}
 /*
  * fd.io coding-style-patch-verification: ON
  *

src/vlib/node.h

@@ -297,6 +297,7 @@ typedef struct vlib_node_t
 #define VLIB_NODE_FLAG_SWITCH_FROM_POLLING_TO_INTERRUPT_MODE (1 << 7)
 #define VLIB_NODE_FLAG_TRACE_SUPPORTED (1 << 8)
 #define VLIB_NODE_FLAG_ADAPTIVE_MODE			     (1 << 9)
+#define VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES		     (1 << 10)
 
   /* State for input nodes. */
   u8 state;

src/vlib/node_funcs.h

@@ -1338,6 +1338,10 @@ void vlib_node_runtime_sync_stats_node (vlib_node_t *n, vlib_node_runtime_t *r,
 /* Node graph initialization function. */
 clib_error_t *vlib_node_main_init (vlib_main_t * vm);
 
+/* Refresh graph after the creation of a node that was potentially mentionned
+ * as a named next for a node with VLIB_NODE_FLAG_ALLOW_LAZY_NEXT_NODES */
+clib_error_t *vlib_node_main_lazy_next_update (vlib_main_t *vm);
+
 format_function_t format_vlib_node_graph;
 format_function_t format_vlib_node_name;
 format_function_t format_vlib_next_node_name;