lib: prepare table code for reuse by bgp_table

  * lib/table.[ch]

    - Add a macro (ROUTE_NODE_FIELDS) that expands to all the fields
      of a route_node structure.

    - Add the route_table_delegate_t structure, a function vector
      which allows clients to customize the behavior of one or more
      tables.

      The delegate currently contains the 'create_node' and
      'destroy_node' functions, and hence enables a table to use an
      alternative node structure. The alternative node is expected to
      embed the fields of a route_node using ROUTE_NODE_FIELDS.

    - Add route_table_init_with_delegate() to create a new table with
      a given delegate.

    - Make route_table_init() a thin wrapper around
      route_table_init_with_delegate(). The delegate it passes in
      simply creates/destroys route_node structures as before.

    - Add a user data pointer (info) to the route_table
      structure. This can be used by a client to keep per-table state.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/lib/table.c b/lib/table.c
index 7efb8c4..6bbc9c6 100644
--- a/lib/table.c
+++ b/lib/table.c
@@ -30,12 +30,17 @@
 static void route_node_delete (struct route_node *);
 static void route_table_free (struct route_table *);
 
+
+/*
+ * route_table_init_with_delegate
+ */
 struct route_table *
-route_table_init (void)
+route_table_init_with_delegate (route_table_delegate_t *delegate)
 {
   struct route_table *rt;
 
   rt = XCALLOC (MTYPE_ROUTE_TABLE, sizeof (struct route_table));
+  rt->delegate = delegate;
   return rt;
 }
 
@@ -47,11 +52,9 @@
 
 /* Allocate new route node. */
 static struct route_node *
-route_node_new (void)
+route_node_new (struct route_table *table)
 {
-  struct route_node *node;
-  node = XCALLOC (MTYPE_ROUTE_NODE, sizeof (struct route_node));
-  return node;
+  return table->delegate->create_node (table->delegate, table);
 }
 
 /* Allocate new route node with prefix set. */
@@ -60,7 +63,7 @@
 {
   struct route_node *node;
   
-  node = route_node_new ();
+  node = route_node_new (table);
 
   prefix_copy (&node->p, prefix);
   node->table = table;
@@ -70,9 +73,9 @@
 
 /* Free route node. */
 static void
-route_node_free (struct route_node *node)
+route_node_free (struct route_table *table, struct route_node *node)
 {
-  XFREE (MTYPE_ROUTE_NODE, node);
+  table->delegate->destroy_node (table->delegate, table, node);
 }
 
 /* Free route table. */
@@ -109,7 +112,7 @@
 
       tmp_node->table->count--;
       tmp_node->lock = 0;  /* to cause assert if unlocked after this */
-      route_node_free (tmp_node);
+      route_node_free (rt, tmp_node);
 
       if (node != NULL)
 	{
@@ -314,7 +317,7 @@
     }
   else
     {
-      new = route_node_new ();
+      new = route_node_new (table);
       route_common (&node->p, p, &new->p);
       new->p.family = p->family;
       new->table = table;
@@ -374,7 +377,7 @@
 
   node->table->count--;
 
-  route_node_free (node);
+  route_node_free (node->table, node);
 
   /* If parent node is stub then delete it also. */
   if (parent && parent->lock == 0)
@@ -482,3 +485,46 @@
 {
   return table->count;
 }
+
+/**
+ * route_node_create
+ *
+ * Default function for creating a route node.
+ */
+static struct route_node *
+route_node_create (route_table_delegate_t *delegate,
+		   struct route_table *table)
+{
+  struct route_node *node;
+  node = XCALLOC (MTYPE_ROUTE_NODE, sizeof (struct route_node));
+  return node;
+}
+
+/**
+ * route_node_destroy
+ *
+ * Default function for destroying a route node.
+ */
+static void
+route_node_destroy (route_table_delegate_t *delegate,
+		    struct route_table *table, struct route_node *node)
+{
+  XFREE (MTYPE_ROUTE_NODE, node);
+}
+
+/*
+ * Default delegate.
+ */
+static route_table_delegate_t default_delegate = {
+  .create_node = route_node_create,
+  .destroy_node = route_node_destroy
+};
+
+/*
+ * route_table_init
+ */
+struct route_table *
+route_table_init (void)
+{
+  return route_table_init_with_delegate (&default_delegate);
+}