bgpd: make bgp_info_cmp and multiple-path decision logic more regular

* bgp_route.c: (bgp_info_cmp) This function is supposed to return a
  preference between the given paths, and does so as binary either or.  When
  mpath was added, the binary return value was left as is and instead an out
  parameter 'paths_eq' was added to indicate the mpath-equality case.  It's
  a bit odd, as is the resulting logic in the caller.

  Regularise things again by making the function return a strcmp like
  trinary return value of -1,0,1.  Get rid of the mpath specific arguments,
  but pass in afi/safi as part of the general context - that plus the
  (struct bgp *) is enough to access configuration.

  Update the return values.

  The mpath check was testing the IGP metric for equality, even though
  previous to the mpath changes (and consistent with the behaviour of all
  the other tests bar the end), equality results in continuing through to
  the next comparison. Just go back to the previous way - each test finds a
  preference to return, or continues on to let further tests have a go.

  (bgp_best_selection) Get rid of the (struct bgp_maxpaths_cfg *) arg, we
  can't add state for every optional feature to the argument list - they
  have to look it up as needed. Do pass through the very general afi/safi
  context though (saves several lookups through the route_node).

  Adjust for the new trinary bgp_info_cmp return value and updated args.
  Do the mpath clearing/accumulation in one place, in each loop.

  Call to bgp_info_mpath_update similarly gets updated, as there's no cfg to
  pass.

  (bgp_process_{rsclient,main}) match bgp_best_selection changes.
* bgp_mpath.c: (bgp_mpath_is_configured_sort) Helper for whether mpath is
  enabled by peer sort.
  (bgp_mpath_is_configured) ditto, generally.
  (bgp_info_mpath_update) caller no longer has the cfg to pass in, look it
  up.
* bgp_mpath.h: Export the above and Match .c changes.

Requires commit:
 "bgpd: bgp_scan shouldn't queue up route_nodes with no routes for processing"

Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

3 files changed, 115 insertions, 90 deletions

diff --git a/bgpd/bgp_mpath.c b/bgpd/bgp_mpath.c
index 7999d16b..98b75b67 100644
--- a/bgpd/bgp_mpath.c
+++ b/bgpd/bgp_mpath.c
@@ -39,6 +39,33 @@
 #include "bgpd/bgp_ecommunity.h"
 #include "bgpd/bgp_mpath.h"
 
+bool
+bgp_mpath_is_configured_sort (struct bgp *bgp, bgp_peer_sort_t sort,
+                              afi_t afi, safi_t safi)
+{
+  struct bgp_maxpaths_cfg *cfg = &bgp->maxpaths[afi][safi];
+
+  /* XXX: BGP_DEFAULT_MAXPATHS is 1, and this test only seems to make sense
+   * if if it stays 1, so not sure the DEFAULT define is that useful.
+   */
+  switch (sort)
+    {
+      case BGP_PEER_IBGP:
+        return cfg->maxpaths_ibgp != BGP_DEFAULT_MAXPATHS;
+      case BGP_PEER_EBGP:
+        return cfg->maxpaths_ebgp != BGP_DEFAULT_MAXPATHS;
+      default:
+        return false;
+    }
+}
+
+bool
+bgp_mpath_is_configured (struct bgp *bgp, afi_t afi, safi_t safi)
+{
+  return bgp_mpath_is_configured_sort (bgp, BGP_PEER_IBGP, afi, safi)
+         || bgp_mpath_is_configured_sort (bgp, BGP_PEER_EBGP, afi, safi);
+}
+
 /*
  * bgp_maximum_paths_set
  *
@@ -395,7 +422,7 @@ bgp_info_mpath_attr_set (struct bgp_info *binfo, struct attr *attr)
 void
 bgp_info_mpath_update (struct bgp_node *rn, struct bgp_info *new_best,
                        struct bgp_info *old_best, struct list *mp_list,
-                       struct bgp_maxpaths_cfg *mpath_cfg)
+                        afi_t afi, safi_t safi)
 {
   u_int16_t maxpaths, mpath_count, old_mpath_count;
   struct listnode *mp_node, *mp_next_node;
@@ -410,8 +437,11 @@ bgp_info_mpath_update (struct bgp_node *rn, struct bgp_info *new_best,
   old_mpath_count = 0;
   prev_mpath = new_best;
   mp_node = listhead (mp_list);
+  struct bgp_maxpaths_cfg *mpath_cfg;
   debug = BGP_DEBUG (events, EVENTS);
 
+  mpath_cfg  = &new_best->peer->bgp->maxpaths[afi][safi];
+
   if (debug)
     prefix2str (&rn->p, pfx_buf, sizeof (pfx_buf));
 
diff --git a/bgpd/bgp_mpath.h b/bgpd/bgp_mpath.h
index 37b9ac8b..2a84d5e1 100644
--- a/bgpd/bgp_mpath.h
+++ b/bgpd/bgp_mpath.h
@@ -51,6 +51,8 @@ struct bgp_info_mpath
 /* Functions to support maximum-paths configuration */
 extern int bgp_maximum_paths_set (struct bgp *, afi_t, safi_t, int, u_int16_t);
 extern int bgp_maximum_paths_unset (struct bgp *, afi_t, safi_t, int);
+bool bgp_mpath_is_configured_sort (struct bgp *, bgp_peer_sort_t, afi_t, safi_t);
+bool bgp_mpath_is_configured (struct bgp *, afi_t, safi_t);
 
 /* Functions used by bgp_best_selection to record current
  * multipath selections
@@ -61,7 +63,7 @@ extern void bgp_mp_list_add (struct list *, struct bgp_info *);
 extern void bgp_mp_dmed_deselect (struct bgp_info *);
 extern void bgp_info_mpath_update (struct bgp_node *, struct bgp_info *,
                                    struct bgp_info *, struct list *,
-                                   struct bgp_maxpaths_cfg *);
+                                   afi_t, safi_t);
 extern void bgp_info_mpath_aggregate_update (struct bgp_info *,
                                              struct bgp_info *);
 
diff --git a/bgpd/bgp_route.c b/bgpd/bgp_route.c
index e0e14eca..8aa6daa8 100644
--- a/bgpd/bgp_route.c
+++ b/bgpd/bgp_route.c
@@ -321,10 +321,12 @@ bgp_med_value (struct attr *attr, struct bgp *bgp)
     }
 }
 
-/* Compare two bgp route entity.  br is preferable then return 1. */
+/* Compare two bgp route entity.  Return -1 if new is preferred, 1 if exist
+ * is preferred, or 0 if they are the same (usually will only occur if
+ * multipath is enabled */
 static int
 bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
-	      int *paths_eq)
+              afi_t afi, safi_t safi)
 {
   struct attr *newattr, *existattr;
   struct attr_extra *newattre, *existattre;
@@ -345,13 +347,11 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
   int confed_as_route;
   int ret;
 
-  *paths_eq = 0;
-
   /* 0. Null check. */
   if (new == NULL)
-    return 0;
-  if (exist == NULL)
     return 1;
+  if (exist == NULL)
+    return -1;
 
   newattr = new->attr;
   existattr = exist->attr;
@@ -367,9 +367,9 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
     exist_weight = existattre->weight;
 
   if (new_weight > exist_weight)
-    return 1;
+    return -1;
   if (new_weight < exist_weight)
-    return 0;
+    return 1;
 
   /* 2. Local preference check. */
   new_pref = exist_pref = bgp->default_local_pref;
@@ -380,9 +380,9 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
     exist_pref = existattr->local_pref;
 
   if (new_pref > exist_pref)
-    return 1;
+    return -1;
   if (new_pref < exist_pref)
-    return 0;
+    return 1;
 
   /* 3. Local route check. We prefer:
    *  - BGP_ROUTE_STATIC
@@ -390,9 +390,9 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
    *  - BGP_ROUTE_REDISTRIBUTE
    */
   if (! (new->sub_type == BGP_ROUTE_NORMAL))
-     return 1;
+     return -1;
   if (! (exist->sub_type == BGP_ROUTE_NORMAL))
-     return 0;
+     return 1;
 
   /* 4. AS path length check. */
   if (! bgp_flag_check (bgp, BGP_FLAG_ASPATH_IGNORE))
@@ -408,26 +408,26 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
           aspath_hops += aspath_count_confeds (newattr->aspath);
           
 	  if ( aspath_hops < (exist_hops + exist_confeds))
-	    return 1;
+	    return -1;
 	  if ( aspath_hops > (exist_hops + exist_confeds))
-	    return 0;
+	    return 1;
 	}
       else
 	{
 	  int newhops = aspath_count_hops (newattr->aspath);
 	  
 	  if (newhops < exist_hops)
-	    return 1;
+	    return -1;
           if (newhops > exist_hops)
-	    return 0;
+	    return 1;
 	}
     }
 
   /* 5. Origin check. */
   if (newattr->origin < existattr->origin)
-    return 1;
+    return -1;
   if (newattr->origin > existattr->origin)
-    return 0;
+    return 1;
 
   /* 6. MED check. */
   internal_as_route = (aspath_count_hops (newattr->aspath) == 0
@@ -448,9 +448,9 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
       exist_med = bgp_med_value (exist->attr, bgp);
 
       if (new_med < exist_med)
-	return 1;
+	return -1;
       if (new_med > exist_med)
-	return 0;
+	return 1;
     }
 
   /* 7. Peer type check. */
@@ -459,10 +459,10 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
 
   if (new_sort == BGP_PEER_EBGP
       && (exist_sort == BGP_PEER_IBGP || exist_sort == BGP_PEER_CONFED))
-    return 1;
+    return -1;
   if (exist_sort == BGP_PEER_EBGP
       && (new_sort == BGP_PEER_IBGP || new_sort == BGP_PEER_CONFED))
-    return 0;
+    return 1;
 
   /* 8. IGP metric check. */
   newm = existm = 0;
@@ -473,41 +473,32 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
     existm = exist->extra->igpmetric;
 
   if (newm < existm)
-    ret = 1;
+    return -1;
   if (newm > existm)
-    ret = 0;
+    return 1;
 
   /* 9. Maximum path check. */
-  if (newm == existm)
+  if (bgp_mpath_is_configured (bgp, afi, safi))
     {
       if (bgp_flag_check(bgp, BGP_FLAG_ASPATH_MULTIPATH_RELAX))
         {
-
-	  /*
-	   * For the two paths, all comparison steps till IGP metric
-	   * have succeeded - including AS_PATH hop count. Since 'bgp
-	   * bestpath as-path multipath-relax' knob is on, we don't need
-	   * an exact match of AS_PATH. Thus, mark the paths are equal.
-	   * That will trigger both these paths to get into the multipath
-	   * array.
-	   */
-	  *paths_eq = 1;
+          /*
+           * For the two paths, all comparison steps till IGP metric
+           * have succeeded - including AS_PATH hop count. Since 'bgp
+           * bestpath as-path multipath-relax' knob is on, we don't need
+           * an exact match of AS_PATH. Thus, mark the paths are equal.
+           * That will trigger both these paths to get into the multipath
+           * array.
+           */
+          return 0;
         }
       else if (new->peer->sort == BGP_PEER_IBGP)
-	{
-	  if (aspath_cmp (new->attr->aspath, exist->attr->aspath))
-	    *paths_eq = 1;
-	}
+        {
+          if (aspath_cmp (new->attr->aspath, exist->attr->aspath))
+            return 0;
+        }
       else if (new->peer->as == exist->peer->as)
-	*paths_eq = 1;
-    }
-  else
-    {
-      /*
-       * TODO: If unequal cost ibgp multipath is enabled we can
-       * mark the paths as equal here instead of returning
-       */
-      return ret;
+        return 0;
     }
 
   /* 10. If both paths are external, prefer the path that was received
@@ -519,9 +510,9 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
       && exist_sort == BGP_PEER_EBGP)
     {
       if (CHECK_FLAG (new->flags, BGP_INFO_SELECTED))
-	return 1;
+	return -1;
       if (CHECK_FLAG (exist->flags, BGP_INFO_SELECTED))
-	return 0;
+	return 1;
     }
 
   /* 11. Router-ID comparision. */
@@ -539,9 +530,9 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
     exist_id.s_addr = exist->peer->remote_id.s_addr;
 
   if (ntohl (new_id.s_addr) < ntohl (exist_id.s_addr))
-    return 1;
+    return -1;
   if (ntohl (new_id.s_addr) > ntohl (exist_id.s_addr))
-    return 0;
+    return 1;
 
   /* 12. Cluster length comparision. */
   new_cluster = exist_cluster = 0;
@@ -552,32 +543,32 @@ bgp_info_cmp (struct bgp *bgp, struct bgp_info *new, struct bgp_info *exist,
     exist_cluster = existattre->cluster->length;
 
   if (new_cluster < exist_cluster)
-    return 1;
+    return -1;
   if (new_cluster > exist_cluster)
-    return 0;
+    return 1;
 
   /* 13. Neighbor address comparision. */
   /* Do this only if neither path is "stale" as stale paths do not have
    * valid peer information (as the connection may or may not be up).
    */
   if (CHECK_FLAG (exist->flags, BGP_INFO_STALE))
-    return 1;
+    return -1;
   if (CHECK_FLAG (new->flags, BGP_INFO_STALE))
-    return 0;
+    return 1;
   /* locally configured routes to advertise do not have su_remote */
   if (new->peer->su_remote == NULL)
-    return 0;
-  if (exist->peer->su_remote == NULL)
     return 1;
+  if (exist->peer->su_remote == NULL)
+    return -1;
   
   ret = sockunion_cmp (new->peer->su_remote, exist->peer->su_remote);
 
   if (ret == 1)
-    return 0;
-  if (ret == -1)
     return 1;
+  if (ret == -1)
+    return -1;
 
-  return 1;
+  return -1;
 }
 
 static enum filter_type
@@ -1325,8 +1316,8 @@ struct bgp_info_pair
 
 static void
 bgp_best_selection (struct bgp *bgp, struct bgp_node *rn,
-		    struct bgp_maxpaths_cfg *mpath_cfg,
-		    struct bgp_info_pair *result)
+		    struct bgp_info_pair *result,
+		    afi_t afi, safi_t safi)
 {
   struct bgp_info *new_select;
   struct bgp_info *old_select;
@@ -1334,7 +1325,7 @@ bgp_best_selection (struct bgp *bgp, struct bgp_node *rn,
   struct bgp_info *ri1;
   struct bgp_info *ri2;
   struct bgp_info *nextri = NULL;
-  int paths_eq, do_mpath;
+  int cmpret, do_mpath;
   struct list mp_list;
     
   result->old = result->new = NULL;
@@ -1349,8 +1340,7 @@ bgp_best_selection (struct bgp *bgp, struct bgp_node *rn,
     }
   
   bgp_mp_list_init (&mp_list);
-  do_mpath = (mpath_cfg->maxpaths_ebgp != BGP_DEFAULT_MAXPATHS ||
-	      mpath_cfg->maxpaths_ibgp != BGP_DEFAULT_MAXPATHS);
+  do_mpath = bgp_mpath_is_configured (bgp, afi, safi);
 
   /* bgp deterministic-med */
   new_select = NULL;
@@ -1388,19 +1378,21 @@ bgp_best_selection (struct bgp *bgp, struct bgp_node *rn,
 		{
 		  if (CHECK_FLAG (ri2->flags, BGP_INFO_SELECTED))
 		    old_select = ri2;
-		  if (bgp_info_cmp (bgp, ri2, new_select, &paths_eq))
+		  if ((cmpret = bgp_info_cmp (bgp, ri2, new_select, afi, safi))
+		       == -1)
 		    {
 		      bgp_info_unset_flag (rn, new_select, BGP_INFO_DMED_SELECTED);
 		      new_select = ri2;
-		      if (do_mpath && !paths_eq)
-			{
-			  bgp_mp_list_clear (&mp_list);
-			  bgp_mp_list_add (&mp_list, ri2);
-			}
 		    }
 
-		  if (do_mpath && paths_eq)
-		    bgp_mp_list_add (&mp_list, ri2);
+		  if (do_mpath)
+		    {
+                      if (cmpret != 0)
+                        bgp_mp_list_clear (&mp_list);
+
+                      if (cmpret == 0 || cmpret == -1)
+                        bgp_mp_list_add (&mp_list, ri2);
+                    }
 
 		  bgp_info_set_flag (rn, ri2, BGP_INFO_DMED_CHECK);
 		}
@@ -1408,7 +1400,7 @@ bgp_best_selection (struct bgp *bgp, struct bgp_node *rn,
 	bgp_info_set_flag (rn, new_select, BGP_INFO_DMED_CHECK);
 	bgp_info_set_flag (rn, new_select, BGP_INFO_DMED_SELECTED);
 
-	bgp_info_mpath_update (rn, new_select, old_select, &mp_list, mpath_cfg);
+	bgp_info_mpath_update (rn, new_select, old_select, &mp_list, afi, safi);
 	bgp_mp_list_clear (&mp_list);
       }
 
@@ -1447,28 +1439,29 @@ bgp_best_selection (struct bgp *bgp, struct bgp_node *rn,
       bgp_info_unset_flag (rn, ri, BGP_INFO_DMED_CHECK);
       bgp_info_unset_flag (rn, ri, BGP_INFO_DMED_SELECTED);
 
-      if (bgp_info_cmp (bgp, ri, new_select, &paths_eq))
+      if ((cmpret = bgp_info_cmp (bgp, ri, new_select, afi, safi)) == -1)
 	{
 	  if (do_mpath && bgp_flag_check (bgp, BGP_FLAG_DETERMINISTIC_MED))
 	    bgp_mp_dmed_deselect (new_select);
 
 	  new_select = ri;
-
-	  if (do_mpath && !paths_eq)
-	    {
-	      bgp_mp_list_clear (&mp_list);
-	      bgp_mp_list_add (&mp_list, ri);
-	    }
 	}
-      else if (do_mpath && bgp_flag_check (bgp, BGP_FLAG_DETERMINISTIC_MED))
+      else if (cmpret == 1 && do_mpath
+               && bgp_flag_check (bgp, BGP_FLAG_DETERMINISTIC_MED))
 	bgp_mp_dmed_deselect (ri);
 
-      if (do_mpath && paths_eq)
-	bgp_mp_list_add (&mp_list, ri);
+      if (do_mpath)
+        {
+          if (cmpret != 0)
+            bgp_mp_list_clear (&mp_list);
+
+          if (cmpret == 0 || cmpret == -1)
+            bgp_mp_list_add (&mp_list, ri);
+        }
     }
 
   if (!bgp_flag_check (bgp, BGP_FLAG_DETERMINISTIC_MED))
-    bgp_info_mpath_update (rn, new_select, old_select, &mp_list, mpath_cfg);
+    bgp_info_mpath_update (rn, new_select, old_select, &mp_list, afi, safi);
 
   bgp_info_mpath_aggregate_update (new_select, old_select);
   bgp_mp_list_clear (&mp_list);
@@ -1552,7 +1545,7 @@ bgp_process_rsclient (struct work_queue *wq, void *data)
   struct peer *rsclient = bgp_node_table (rn)->owner;
   
   /* Best path selection. */
-  bgp_best_selection (bgp, rn, &bgp->maxpaths[afi][safi], &old_and_new);
+  bgp_best_selection (bgp, rn, &old_and_new, afi, safi);
   new_select = old_and_new.new;
   old_select = old_and_new.old;
 
@@ -1615,7 +1608,7 @@ bgp_process_main (struct work_queue *wq, void *data)
   struct peer *peer;
   
   /* Best path selection. */
-  bgp_best_selection (bgp, rn, &bgp->maxpaths[afi][safi], &old_and_new);
+  bgp_best_selection (bgp, rn, &old_and_new, afi, safi);
   old_select = old_and_new.old;
   new_select = old_and_new.new;