bgpd, zebra: auto assign labels from label pool to regular prefixes in BGP labeled unicast

This commit is the last missing piece to complete BGP LU support in bgpd. To this moment, bgpd (and zebra) supported auto label assignment only for prefixes leaked from VRFs to vpn and for MPLS SR prefixes. This adds auto label assignment to other routes types in bgpd. The following enhancements have been made:
* bgp_route.c:bgp_process_main_one() now sets implicit-null local_label to all local, aggregate and redistributed routes.
* bgp_route.c:bgp_process_main_one() now will request a label from the label pool for any prefix that loses the label for some reason (for example, when the static label assignment config is removed)
* bgp_label.c:bgp_reg_dereg_for_label() now requests labels from label pool for routes which have no associated label index
* zebra_mpls.c:zebra_mpls_fec_register() now expects both label and label_index from the calling function, one of which must be set to MPLS_INVALID_LABEL or MPLS_INVALID_LABEL_INDEX, based on this it will decide how to register the provided FEC.

Signed-off-by: Anton Degtyarev <anton@cumulusnetworks.com>

1 files changed, 44 insertions, 20 deletions

diff --git a/zebra/zebra_mpls.c b/zebra/zebra_mpls.c
index 5fe0116158..c0764cd4b8 100644
--- a/zebra/zebra_mpls.c
+++ b/zebra/zebra_mpls.c
@@ -1813,17 +1813,22 @@ int zebra_mpls_lsp_uninstall(struct zebra_vrf *zvrf, struct route_node *rn,
  * NOTE: If there is a manually configured label binding, that is used.
  * Otherwise, if a label index is specified, it means we have to allocate the
  * label from a locally configured label block (SRGB), if one exists and index
- * is acceptable.
+ * is acceptable. If no label index then just register the specified label.
+ * NOTE2: Either label or label_index is expected to be set to MPLS_INVALID_*
+ * by the calling function. Register requests with both will be rejected.
  */
 int zebra_mpls_fec_register(struct zebra_vrf *zvrf, struct prefix *p,
-			    uint32_t label_index, struct zserv *client)
+			    uint32_t label, uint32_t label_index,
+			    struct zserv *client)
 {
 	struct route_table *table;
 	zebra_fec_t *fec;
 	char buf[BUFSIZ];
-	int new_client;
-	int label_change = 0;
+	bool new_client;
+	bool label_change = false;
 	uint32_t old_label;
+	bool have_label_index = (label_index != MPLS_INVALID_LABEL_INDEX);
+	bool is_configured_fec = false; /* indicate statically configured FEC */
 
 	table = zvrf->fec_table[family2afi(PREFIX_FAMILY(p))];
 	if (!table)
@@ -1832,12 +1837,20 @@ int zebra_mpls_fec_register(struct zebra_vrf *zvrf, struct prefix *p,
 	if (IS_ZEBRA_DEBUG_MPLS)
 		prefix2str(p, buf, BUFSIZ);
 
+	if (label != MPLS_INVALID_LABEL && have_label_index) {
+		flog_err(
+			EC_ZEBRA_FEC_LABEL_INDEX_LABEL_CONFLICT,
+			"Rejecting FEC register for %s with both label %u and Label Index %u specified, client %s",
+			buf, label, label_index,
+			zebra_route_string(client->proto));
+		return -1;
+	}
+
 	/* Locate FEC */
 	fec = fec_find(table, p);
 	if (!fec) {
-		fec = fec_add(table, p, MPLS_INVALID_LABEL, 0, label_index);
+		fec = fec_add(table, p, label, 0, label_index);
 		if (!fec) {
-			prefix2str(p, buf, BUFSIZ);
 			flog_err(
 				EC_ZEBRA_FEC_ADD_FAILED,
 				"Failed to add FEC %s upon register, client %s",
@@ -1846,16 +1859,19 @@ int zebra_mpls_fec_register(struct zebra_vrf *zvrf, struct prefix *p,
 		}
 
 		old_label = MPLS_INVALID_LABEL;
-		new_client = 1;
+		new_client = true;
 	} else {
+		/* Check if the FEC has been statically defined in the config */
+		is_configured_fec = fec->flags & FEC_FLAG_CONFIGURED;
 		/* Client may register same FEC with different label index. */
 		new_client =
 			(listnode_lookup(fec->client_list, client) == NULL);
-		if (!new_client && fec->label_index == label_index)
+		if (!new_client && fec->label_index == label_index
+		    && fec->label == label)
 			/* Duplicate register */
 			return 0;
 
-		/* Save current label, update label index */
+		/* Save current label, update the FEC */
 		old_label = fec->label;
 		fec->label_index = label_index;
 	}
@@ -1864,21 +1880,29 @@ int zebra_mpls_fec_register(struct zebra_vrf *zvrf, struct prefix *p,
 		listnode_add(fec->client_list, client);
 
 	if (IS_ZEBRA_DEBUG_MPLS)
-		zlog_debug("FEC %s Label Index %u %s by client %s", buf,
-			   label_index, new_client ? "registered" : "updated",
-			   zebra_route_string(client->proto));
-
-	/* If not a configured FEC, derive the local label (from label index)
-	 * or reset it.
+		zlog_debug("FEC %s label%s %u %s by client %s%s", buf,
+			   have_label_index ? " index" : "",
+			   have_label_index ? label_index : label,
+			   new_client ? "registered" : "updated",
+			   zebra_route_string(client->proto),
+			   is_configured_fec
+				   ? ", but using statically configured label"
+				   : "");
+
+	/* If not a statically configured FEC, derive the local label
+	 * from label index or use the provided label
 	 */
-	if (!(fec->flags & FEC_FLAG_CONFIGURED)) {
-		fec_derive_label_from_index(zvrf, fec);
+	if (!is_configured_fec) {
+		if (have_label_index)
+			fec_derive_label_from_index(zvrf, fec);
+		else
+			fec->label = label;
 
 		/* If no label change, exit. */
 		if (fec->label == old_label)
 			return 0;
 
-		label_change = 1;
+		label_change = true;
 	}
 
 	/* If new client or label change, update client and install or uninstall
@@ -2106,8 +2130,8 @@ int zebra_mpls_static_fec_del(struct zebra_vrf *zvrf, struct prefix *p)
 
 	if (IS_ZEBRA_DEBUG_MPLS) {
 		prefix2str(p, buf, BUFSIZ);
-		zlog_debug("Delete fec %s label index %u", buf,
-			   fec->label_index);
+		zlog_debug("Delete fec %s label %u label index %u", buf,
+			   fec->label, fec->label_index);
 	}
 
 	old_label = fec->label;