zebra, lib: upon lsp install, iterate nexthop accordingly

There are two ways of iterating over nexthops of a given
route entry.
- Either only the main nexthop are taken into account
(which is the case today when attempting to install an
LSP entry on a BGP connected labeled route.
- Or by taking into account nexthops that are resolved
and linked in nexthop->resolved of the previous nexthop
which has RECURSIVE flag set. This second case has to be
taken into account in the case where recursive routes may
be used to install an LSP entry.

Introduce a new API in nexthop that will parse over the
appropriate nexthop, if the nexthop-resolution flag is turned
on or not on the given VRF.

Use that API in the lsp_install() function so as to walk
over the appropriate nexthops.

Co-developed-by: Dmytro Shytyi <dmytro.shytyi@6wind.com>
Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>
Signed-off-by: Dmytro Shytyi <dmytro.shytyi@6wind.com>

3 files changed, 32 insertions, 6 deletions

diff --git a/lib/nexthop.c b/lib/nexthop.c
index 26c338256f..d6c654a692 100644
--- a/lib/nexthop.c
+++ b/lib/nexthop.c
@@ -699,6 +699,15 @@ struct nexthop *nexthop_next(const struct nexthop *nexthop)
 	return NULL;
 }
 
+struct nexthop *nexthop_next_resolution(const struct nexthop *nexthop,
+					bool nexthop_resolution)
+{
+	if (nexthop_resolution)
+		return nexthop_next(nexthop);
+	/* no resolution attempt */
+	return nexthop->next;
+}
+
 /* Return the next nexthop in the tree that is resolved and active */
 struct nexthop *nexthop_next_active_resolved(const struct nexthop *nexthop)
 {
diff --git a/lib/nexthop.h b/lib/nexthop.h
index 27073b948d..457c81972e 100644
--- a/lib/nexthop.h
+++ b/lib/nexthop.h
@@ -223,6 +223,8 @@ extern bool nexthop_labels_match(const struct nexthop *nh1,
 extern const char *nexthop2str(const struct nexthop *nexthop,
 			       char *str, int size);
 extern struct nexthop *nexthop_next(const struct nexthop *nexthop);
+extern struct nexthop *nexthop_next_resolution(const struct nexthop *nexthop,
+					       bool nexthop_resolution);
 extern struct nexthop *
 nexthop_next_active_resolved(const struct nexthop *nexthop);
 extern unsigned int nexthop_level(const struct nexthop *nexthop);
diff --git a/zebra/zebra_mpls.c b/zebra/zebra_mpls.c
index ca93ce8fbd..17fe455741 100644
--- a/zebra/zebra_mpls.c
+++ b/zebra/zebra_mpls.c
@@ -161,12 +161,14 @@ static int lsp_install(struct zebra_vrf *zvrf, mpls_label_t label,
 	enum lsp_types_t lsp_type;
 	char buf[BUFSIZ];
 	int added, changed;
+	bool zvrf_nexthop_resolution;
 
 	/* Lookup table. */
 	lsp_table = zvrf->lsp_table;
 	if (!lsp_table)
 		return -1;
 
+	zvrf_nexthop_resolution = zvrf->zebra_mpls_fec_nexthop_resolution;
 	lsp_type = lsp_type_from_re_type(re->type);
 	added = changed = 0;
 
@@ -180,13 +182,20 @@ static int lsp_install(struct zebra_vrf *zvrf, mpls_label_t label,
 	 * the label advertised by the recursive nexthop (plus we don't have the
 	 * logic yet to push multiple labels).
 	 */
-	for (nexthop = re->nhe->nhg.nexthop;
-	     nexthop; nexthop = nexthop->next) {
-		/* Skip inactive and recursive entries. */
-		if (!CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_ACTIVE))
+	nexthop = re->nhe->nhg.nexthop;
+	while (nexthop) {
+		if (!CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_ACTIVE)) {
+			nexthop =
+				nexthop_next_resolution(nexthop,
+							zvrf_nexthop_resolution);
 			continue;
-		if (CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_RECURSIVE))
+		}
+		if (CHECK_FLAG(nexthop->flags, NEXTHOP_FLAG_RECURSIVE)) {
+			nexthop =
+				nexthop_next_resolution(nexthop,
+							zvrf_nexthop_resolution);
 			continue;
+		}
 
 		nhlfe = nhlfe_find(&lsp->nhlfe_list, lsp_type,
 				   nexthop->type, &nexthop->gate,
@@ -194,9 +203,13 @@ static int lsp_install(struct zebra_vrf *zvrf, mpls_label_t label,
 		if (nhlfe) {
 			/* Clear deleted flag (in case it was set) */
 			UNSET_FLAG(nhlfe->flags, NHLFE_FLAG_DELETED);
-			if (nexthop_labels_match(nhlfe->nexthop, nexthop))
+			if (nexthop_labels_match(nhlfe->nexthop, nexthop)) {
 				/* No change */
+				nexthop =
+					nexthop_next_resolution(nexthop,
+								zvrf_nexthop_resolution);
 				continue;
+			}
 
 
 			if (IS_ZEBRA_DEBUG_MPLS) {
@@ -234,6 +247,8 @@ static int lsp_install(struct zebra_vrf *zvrf, mpls_label_t label,
 			SET_FLAG(nhlfe->flags, NHLFE_FLAG_CHANGED);
 			added++;
 		}
+		nexthop = nexthop_next_resolution(nexthop,
+						  zvrf_nexthop_resolution);
 	}
 
 	/* Queue LSP for processing if necessary. If no NHLFE got added (special