isisd: Add func to unset the SRv6 locator

Add a function to unset the SRv6 locator for a specific IS-IS area.

This function calls `isis_zebra_srv6_manager_release_locator_chunk()` to
ask zebra to release the locator chunk owned by IS-IS and removes the
chunk from the area's chunks list.

Signed-off-by: Carmine Scarpitta <carmine.scarpitta@uniroma2.it>

isisd/isis_srv6.c

@@ -15,6 +15,55 @@
 #include "isisd/isisd.h"
 #include "isisd/isis_misc.h"
 #include "isisd/isis_srv6.h"
+#include "isisd/isis_zebra.h"
+
+/**
+ * Unset the SRv6 locator for a given IS-IS area.
+ *
+ * @param area	IS-IS area
+ *
+ * @result True on success, False otherwise
+ */
+bool isis_srv6_locator_unset(struct isis_area *area)
+{
+	int ret;
+	struct listnode *node, *nnode;
+	struct srv6_locator_chunk *chunk;
+
+	if (strncmp(area->srv6db.config.srv6_locator_name, "",
+		    sizeof(area->srv6db.config.srv6_locator_name)) == 0) {
+		sr_debug("SRv6 locator not set");
+		return true;
+	}
+
+	/* Inform Zebra that we are releasing the SRv6 locator */
+	ret = isis_zebra_srv6_manager_release_locator_chunk(
+		area->srv6db.config.srv6_locator_name);
+	if (ret < 0)
+		return false;
+
+	/* Delete chunks */
+	for (ALL_LIST_ELEMENTS(area->srv6db.srv6_locator_chunks, node, nnode,
+			       chunk)) {
+		sr_debug(
+			"Releasing chunk of locator %s (prefix %pFX) for IS-IS area %s",
+			area->srv6db.config.srv6_locator_name, &chunk->prefix,
+			area->area_tag);
+
+		listnode_delete(area->srv6db.srv6_locator_chunks, chunk);
+		srv6_locator_chunk_free(&chunk);
+	}
+
+	/* Clear locator name */
+	memset(area->srv6db.config.srv6_locator_name, 0,
+	       sizeof(area->srv6db.config.srv6_locator_name));
+
+	/* Regenerate LSPs to advertise that the SRv6 locator no longer exists
+	 */
+	lsp_regenerate_schedule(area, area->is_type, 0);
+
+	return true;
+}
 
 /**
  * Show Segment Routing over IPv6 (SRv6) Node.

isisd/isis_srv6.h

@@ -44,6 +44,8 @@ struct isis_srv6_db {
 	} config;
 };
 
+bool isis_srv6_locator_unset(struct isis_area *area);
+
 extern void isis_srv6_area_init(struct isis_area *area);
 extern void isis_srv6_area_term(struct isis_area *area);