ospfd: Correct Segment Routing prefix bugs

This patch solves 2 Segment Routing prefix bugs:

- If Segment Routing is not enabled in the initial configuration, Extended
  Prefix Opaque LSA is not flood. This is due to a control flag which is
  set only when Segment Routing is enabled at startup and not latter.
- Attempting to modify Segment Routing prefix flag e.g. adding or removing
  no-php or explicit-null flag, doesn't work as expected: Corresponding entry
  in the MPLS table is not updated, Extended Prefix Opaque LSA carry wrong flag
  value, and neighbor set a wrong configuration in the MPLS table for this
  Segment Routing prefix.

The first bug is corrected in ospfd/ospf_ext.c:

- Flag setting is moved from ospf_ext_ism_change() to set_ext_prefix() function

The seconf one is corrected in ospfd/ospf_sr.c:

- For self node, previous MPLS entry is removed if needed and flag reset before
  setting the new Segment Routing prefix configuration
- For neighbor node, srnext field of sr_prefix structure is always set and not
  only for new SR Prefix.

Signed-off-by: Olivier Dugeon <olivier.dugeon@orange.com>

ospfd/ospf_ext.c

@@ -301,6 +301,8 @@ static void set_ext_prefix(struct ext_itf *exti, uint8_t route_type,
 	exti->prefix.af = 0;
 	exti->prefix.pref_length = p.prefixlen;
 	exti->prefix.address = p.prefix;
+
+	SET_FLAG(exti->flags, EXT_LPFLG_LSA_ACTIVE);
 }
 
 /* Extended Link TLV - RFC7684 section 3.1 */
@@ -766,7 +768,6 @@ static void ospf_ext_ism_change(struct ospf_interface *oi, int old_status)
 		if (OspfEXT.enabled) {
 			osr_debug("EXT (%s): Set Prefix SID to interface %s ",
 				  __func__, oi->ifp->name);
-			exti->flags = EXT_LPFLG_LSA_ACTIVE;
 			ospf_sr_update_local_prefix(oi->ifp, oi->address);
 		}
 	} else {

ospfd/ospf_sr.c

@@ -1202,16 +1202,22 @@ static void update_ext_prefix_sid(struct sr_node *srn, struct sr_prefix *srp)
 		  found ? "Update" : "Add", GET_OPAQUE_ID(srp->instance),
 		  &srn->adv_router);
 
+	/* Complete SR-Prefix */
+	srp->srn = srn;
+	IPV4_ADDR_COPY(&srp->adv_router, &srn->adv_router);
+
 	/* if not found, add new Segment Prefix and install NHLFE */
 	if (!found) {
-		/* Complete SR-Prefix and add it to SR-Node list */
-		srp->srn = srn;
-		IPV4_ADDR_COPY(&srp->adv_router, &srn->adv_router);
+		/* Add it to SR-Node list ... */
 		listnode_add(srn->ext_prefix, srp);
-		/* Try to set MPLS table */
+		/* ... and try to set MPLS table */
 		if (compute_prefix_nhlfe(srp) == 1)
 			ospf_zebra_update_prefix_sid(srp);
 	} else {
+		/*
+		 * An old SR prefix exist. Check if something changes or if it
+		 * is just a refresh.
+		 */
 		if (sr_prefix_cmp(pref, srp)) {
 			if (compute_prefix_nhlfe(srp) == 1) {
 				ospf_zebra_delete_prefix_sid(pref);
@@ -2462,10 +2468,18 @@ DEFUN (sr_prefix_sid,
 		new->type = LOCAL_SID;
 	}
 
+	/* First, remove old NHLFE if installed */
+	if (srp == new && CHECK_FLAG(srp->flags, EXT_SUBTLV_PREFIX_SID_NPFLG)
+	    && !CHECK_FLAG(srp->flags, EXT_SUBTLV_PREFIX_SID_EFLG))
+		ospf_zebra_delete_prefix_sid(srp);
+	/* Then, reset Flag & labels to handle flag update */
+	new->flags = 0;
+	new->label_in = 0;
+	new->nhlfe.label_out = 0;
+
 	/* Set NO PHP flag if present and compute NHLFE */
 	if (argv_find(argv, argc, "no-php-flag", &idx)) {
 		SET_FLAG(new->flags, EXT_SUBTLV_PREFIX_SID_NPFLG);
-		UNSET_FLAG(new->flags, EXT_SUBTLV_PREFIX_SID_EFLG);
 		new->label_in = index2label(new->sid, OspfSR.self->srgb);
 		new->nhlfe.label_out = MPLS_LABEL_IMPLICIT_NULL;
 	}
@@ -2505,7 +2519,7 @@ DEFUN (sr_prefix_sid,
 	if (srp != new)
 		listnode_add(OspfSR.self->ext_prefix, new);
 
-	/* Install Prefix SID if SR is UP and a valid input label set */
+	/* Update Prefix SID if SR is UP */
 	if (OspfSR.status == SR_UP) {
 		if (CHECK_FLAG(new->flags, EXT_SUBTLV_PREFIX_SID_NPFLG)
 		    && !CHECK_FLAG(new->flags, EXT_SUBTLV_PREFIX_SID_EFLG))

ospfd/ospf_zebra.c

@@ -622,7 +622,7 @@ void ospf_zebra_update_prefix_sid(const struct sr_prefix *srp)
 			znh->labels[0] = path->srni.label_out;
 
 			osr_debug("  |- labels %u/%u", srp->label_in,
-				  srp->nhlfe.label_out);
+				  path->srni.label_out);
 
 			/* Set TI-LFA backup nexthop info if present */
 			if (path->srni.backup_label_stack) {