zebra: add installed nexthop-group id value

In some cases, zebra may install a nexthop-group id that is
different from the id of the nhe struct attached to a
route-entry. This happens for a singleton recursive nexthop,
for example, where a route is installed with the resolving
nexthop's id.

The installed value is the most useful value - that corresponds
to information in the kernel on linux/netlink platforms that
support nhgs. Display both values if they differ in ascii
output, and include both values in the json form.

Signed-off-by: Mark Stapp <mstapp@nvidia.com>

4 files changed, 33 insertions, 10 deletions

diff --git a/zebra/rib.h b/zebra/rib.h
index 076608bb0f..fa8193bedf 100644
--- a/zebra/rib.h
+++ b/zebra/rib.h
@@ -108,8 +108,11 @@ struct route_entry {
 	struct nexthop_group fib_ng;
 	struct nexthop_group fib_backup_ng;
 
-	/* Nexthop group hash entry ID */
+	/* Nexthop group hash entry IDs. The "installed" id is the id
+	 * used in linux/netlink, if available.
+	 */
 	uint32_t nhe_id;
+	uint32_t nhe_installed_id;
 
 	/* Tag */
 	route_tag_t tag;
diff --git a/zebra/zebra_dplane.c b/zebra/zebra_dplane.c
index 4000272544..bf34fb54a9 100644
--- a/zebra/zebra_dplane.c
+++ b/zebra/zebra_dplane.c
@@ -2448,6 +2448,8 @@ int dplane_ctx_route_init(struct zebra_dplane_ctx *ctx, enum dplane_op_e op,
 			ret = ENOENT;
 			goto done;
 		}
+
+		re->nhe_installed_id = nhe->id;
 	}
 #endif /* HAVE_NETLINK */
 
diff --git a/zebra/zebra_rib.c b/zebra/zebra_rib.c
index 3df70a3b56..625c966301 100644
--- a/zebra/zebra_rib.c
+++ b/zebra/zebra_rib.c
@@ -305,35 +305,41 @@ static void route_entry_attach_ref(struct route_entry *re,
 {
 	re->nhe = new;
 	re->nhe_id = new->id;
+	re->nhe_installed_id = 0;
 
 	zebra_nhg_increment_ref(new);
 }
 
+/* Replace (if 'new_nhghe') or clear (if that's NULL) an re's nhe. */
 int route_entry_update_nhe(struct route_entry *re,
 			   struct nhg_hash_entry *new_nhghe)
 {
-	struct nhg_hash_entry *old;
 	int ret = 0;
+	struct nhg_hash_entry *old_nhg = NULL;
 
 	if (new_nhghe == NULL) {
-		if (re->nhe)
-			zebra_nhg_decrement_ref(re->nhe);
+		old_nhg = re->nhe;
+
+		re->nhe_id = 0;
+		re->nhe_installed_id = 0;
 		re->nhe = NULL;
 		goto done;
 	}
 
 	if ((re->nhe_id != 0) && re->nhe && (re->nhe != new_nhghe)) {
-		old = re->nhe;
+		/* Capture previous nhg, if any */
+		old_nhg = re->nhe;
 
 		route_entry_attach_ref(re, new_nhghe);
-
-		if (old)
-			zebra_nhg_decrement_ref(old);
 	} else if (!re->nhe)
 		/* This is the first time it's being attached */
 		route_entry_attach_ref(re, new_nhghe);
 
 done:
+	/* Detach / deref previous nhg */
+	if (old_nhg)
+		zebra_nhg_decrement_ref(old_nhg);
+
 	return ret;
 }
 
@@ -3093,7 +3099,8 @@ void rib_unlink(struct route_node *rn, struct route_entry *re)
 
 	if (re->nhe && re->nhe_id) {
 		assert(re->nhe->id == re->nhe_id);
-		zebra_nhg_decrement_ref(re->nhe);
+
+		route_entry_update_nhe(re, NULL);
 	} else if (re->nhe && re->nhe->nhg.nexthop)
 		nexthops_free(re->nhe->nhg.nexthop);
 
diff --git a/zebra/zebra_vty.c b/zebra/zebra_vty.c
index a3faa3d3e2..298697907b 100644
--- a/zebra/zebra_vty.c
+++ b/zebra/zebra_vty.c
@@ -540,8 +540,14 @@ static void vty_show_ip_route_detail(struct vty *vty, struct route_node *rn,
 
 		vty_out(vty, "  Last update %s ago\n", buf);
 
-		if (show_ng)
+		if (show_ng) {
 			vty_out(vty, "  Nexthop Group ID: %u\n", re->nhe_id);
+			if (re->nhe_installed_id != 0
+			    && re->nhe_id != re->nhe_installed_id)
+				vty_out(vty,
+					"  Installed Nexthop Group ID: %u\n",
+					re->nhe_installed_id);
+		}
 
 		for (ALL_NEXTHOPS(re->nhe->nhg, nexthop)) {
 			/* Use helper to format each nexthop */
@@ -977,6 +983,11 @@ static void vty_show_ip_route(struct vty *vty, struct route_node *rn,
 					    &(re->nhe->nhg)));
 		json_object_int_add(json_route, "nexthopGroupId", re->nhe_id);
 
+		if (re->nhe_installed_id != 0)
+			json_object_int_add(json_route,
+					    "installedNexthopGroupId",
+					    re->nhe_installed_id);
+
 		json_object_string_add(json_route, "uptime", up_str);
 
 		for (ALL_NEXTHOPS_PTR(nhg, nexthop)) {