bgpd: Adds equal-paths check to path comparison. Paths that are

equal to the best path are accumulated onto an ordered list (mp_list)
if maximum-paths is configured. A future commit will add the
multipath markup to the BGP rib table based on the mp_list. Add
unit test for the added mp_list functions.

Deterministic MED is not supported in this commit, it will be
added later.

* bgpd/bgp_aspath.c
  * Make aspath_cmp() an external symbol so it can be used in
    equivalent paths check
* bgpd/bgp_aspath.h
  * Add extern declaration of aspath_cmp()
* bgpd/bgp_mpath.c
  * bgp_info_nexthop_cmp(): Compares nexthops of two paths
  * bgp_info_mpath_cmp(): Compare function to order multipaths by
    nexthop and then by peer address
  * bgp_mp_list_init(): Initialize a list with the multipath order function
  * bgp_mp_list_clear(): Clear out the mp_list
  * bgp_mp_list_add(): Add a multipath to mp_list
* bgpd/bgp_mpath.h
  * External declarations for above added functions in bgp_mpath.c
* bgpd/bgp_route.c
  * bgp_info_cmp(): Add equivalent paths result (paths_eq). If eBGP
    paths are equal down to IGP metric check, flag as equal if peer AS
    matches. Similarly for iBGP paths but compare full AS_PATH.
  * bgp_best_selection(): If multipath is enabled, accumulate equivalent paths
    in mp_list. Add debug bgp event output to see result (will be filtered
    later to display only when change occurs)
  * bgp_process_rsclient(): Pass multipath config to bgp_best_selection()
  * bgp_process_main(): Pass multipath config to bgp_best_selection()
* tests/bgp_mpath_test.c
  * Add unit test case for bgp_mp_list functions

1 files changed, 119 insertions, 0 deletions

diff --git a/bgpd/bgp_mpath.c b/bgpd/bgp_mpath.c
index 56c703f6d..09b469516 100644
--- a/bgpd/bgp_mpath.c
+++ b/bgpd/bgp_mpath.c
@@ -24,8 +24,14 @@
 #include <zebra.h>
 
 #include "command.h"
+#include "prefix.h"
+#include "linklist.h"
+#include "sockunion.h"
 
 #include "bgpd/bgpd.h"
+#include "bgpd/bgp_table.h"
+#include "bgpd/bgp_route.h"
+#include "bgpd/bgp_attr.h"
 #include "bgpd/bgp_mpath.h"
 
 /*
@@ -81,3 +87,116 @@ bgp_maximum_paths_unset (struct bgp *bgp, afi_t afi, safi_t safi,
 
   return 0;
 }
+
+/*
+ * bgp_info_nexthop_cmp
+ *
+ * Compare the nexthops of two paths. Return value is less than, equal to,
+ * or greater than zero if bi1 is respectively less than, equal to,
+ * or greater than bi2.
+ */
+static int
+bgp_info_nexthop_cmp (struct bgp_info *bi1, struct bgp_info *bi2)
+{
+  struct attr_extra *ae1, *ae2;
+  int compare;
+
+  ae1 = bgp_attr_extra_get (bi1->attr);
+  ae2 = bgp_attr_extra_get (bi2->attr);
+
+  compare = IPV4_ADDR_CMP (&bi1->attr->nexthop, &bi2->attr->nexthop);
+
+  if (!compare && ae1 && ae2 && (ae1->mp_nexthop_len == ae2->mp_nexthop_len))
+    {
+      switch (ae1->mp_nexthop_len)
+        {
+        case 4:
+        case 12:
+          compare = IPV4_ADDR_CMP (&ae1->mp_nexthop_global_in,
+                                   &ae2->mp_nexthop_global_in);
+          break;
+#ifdef HAVE_IPV6
+        case 16:
+          compare = IPV6_ADDR_CMP (&ae1->mp_nexthop_global,
+                                   &ae2->mp_nexthop_global);
+          break;
+        case 32:
+          compare = IPV6_ADDR_CMP (&ae1->mp_nexthop_global,
+                                   &ae2->mp_nexthop_global);
+          if (!compare)
+            compare = IPV6_ADDR_CMP (&ae1->mp_nexthop_local,
+                                     &ae2->mp_nexthop_local);
+          break;
+#endif /* HAVE_IPV6 */
+        }
+    }
+
+  return compare;
+}
+
+/*
+ * bgp_info_mpath_cmp
+ *
+ * This function determines our multipath list ordering. By ordering
+ * the list we can deterministically select which paths are included
+ * in the multipath set. The ordering also helps in detecting changes
+ * in the multipath selection so we can detect whether to send an
+ * update to zebra.
+ *
+ * The order of paths is determined first by received nexthop, and then
+ * by peer address if the nexthops are the same.
+ */
+static int
+bgp_info_mpath_cmp (void *val1, void *val2)
+{
+  struct bgp_info *bi1, *bi2;
+  int compare;
+
+  bi1 = val1;
+  bi2 = val2;
+
+  compare = bgp_info_nexthop_cmp (bi1, bi2);
+
+  if (!compare)
+    compare = sockunion_cmp (bi1->peer->su_remote, bi2->peer->su_remote);
+
+  return compare;
+}
+
+/*
+ * bgp_mp_list_init
+ *
+ * Initialize the mp_list, which holds the list of multipaths
+ * selected by bgp_best_selection
+ */
+void
+bgp_mp_list_init (struct list *mp_list)
+{
+  assert (mp_list);
+  memset (mp_list, 0, sizeof (struct list));
+  mp_list->cmp = bgp_info_mpath_cmp;
+}
+
+/*
+ * bgp_mp_list_clear
+ *
+ * Clears all entries out of the mp_list
+ */
+void
+bgp_mp_list_clear (struct list *mp_list)
+{
+  assert (mp_list);
+  list_delete_all_node (mp_list);
+}
+
+/*
+ * bgp_mp_list_add
+ *
+ * Adds a multipath entry to the mp_list
+ */
+void
+bgp_mp_list_add (struct list *mp_list, struct bgp_info *mpinfo)
+{
+  assert (mp_list && mpinfo);
+  listnode_add_sort (mp_list, mpinfo);
+}