zebra: label manager refactor

in order to both streamline the code and allow users to
define their own specialized versions of the LM api handlers,
define hooks for the 4 main primitives offered by the label
manager (i.e. connect, disconnect, get_chunk and release_chunk),
and have the existing code be run in response to a hook_call.
Additionally, have the responses to the requesting daemon be
callable from an external API.

Note that the proxy version of the label manager was a source of
issues and hardly used in practice. With the new hooks, users with
more complex requirements can simply plug in their own code to
handle label distribution remotely, so there is no longer a reason
to maintain this code.

Signed-off-by: Emanuele Di Pascale <emanuele@voltanet.io>

7 files changed, 220 insertions, 382 deletions

diff --git a/zebra/label_manager.c b/zebra/label_manager.c
index 6de94e63d..03cfa572d 100644
--- a/zebra/label_manager.c
+++ b/zebra/label_manager.c
@@ -38,295 +38,65 @@
 #include "zebra/zebra_router.h"
 #include "zebra/label_manager.h"
 #include "zebra/zebra_errors.h"
+#include "zebra/zapi_msg.h"
 
 #define CONNECTION_DELAY 5
 
 struct label_manager lbl_mgr;
 
-extern struct zebra_privs_t zserv_privs;
-
 DEFINE_MGROUP(LBL_MGR, "Label Manager");
 DEFINE_MTYPE_STATIC(LBL_MGR, LM_CHUNK, "Label Manager Chunk");
 
-/* In case this zebra daemon is not acting as label manager,
- * it will be a proxy to relay messages to external label manager
- * This zclient thus is to connect to it
+/* define hooks for the basic API, so that it can be specialized or served
+ * externally
  */
-static struct stream *obuf;
-static struct zclient *zclient;
-bool lm_is_external;
 
-static void delete_label_chunk(void *val)
+DEFINE_HOOK(lm_client_connect,
+	    (uint8_t proto, uint16_t instance, vrf_id_t vrf_id),
+	    (proto, instance, vrf_id));
+DEFINE_HOOK(lm_client_disconnect, (uint8_t proto, uint16_t instance),
+	    (proto, instance));
+DEFINE_HOOK(lm_get_chunk,
+	    (struct label_manager_chunk * *lmc, uint8_t proto,
+	     uint16_t instance, uint8_t keep, uint32_t size, uint32_t base,
+	     vrf_id_t vrf_id),
+	    (lmc, proto, instance, keep, size, base, vrf_id));
+DEFINE_HOOK(lm_release_chunk,
+	    (uint8_t proto, uint16_t instance, uint32_t start, uint32_t end),
+	    (proto, instance, start, end));
+DEFINE_HOOK(lm_cbs_inited, (), ());
+
+/* define wrappers to be called in zapi_msg.c (as hooks must be called in
+ * source file where they were defined)
+ */
+void lm_client_connect_call(uint8_t proto, uint16_t instance, vrf_id_t vrf_id)
 {
-	XFREE(MTYPE_LM_CHUNK, val);
+	hook_call(lm_client_connect, proto, instance, vrf_id);
 }
-
-static int relay_response_back(void)
+void lm_get_chunk_call(struct label_manager_chunk **lmc, uint8_t proto,
+		       uint16_t instance, uint8_t keep, uint32_t size,
+		       uint32_t base, vrf_id_t vrf_id)
 {
-	int ret = 0;
-	struct stream *src, *dst;
-	uint16_t size = 0;
-	uint8_t marker;
-	uint8_t version;
-	vrf_id_t vrf_id;
-	uint16_t resp_cmd;
-	uint8_t proto;
-	const char *proto_str;
-	unsigned short instance;
-	struct zserv *zserv;
-
-	/* sanity */
-	if (!zclient || zclient->sock < 0)
-		return -1;
-
-	/* input buffer with msg from label manager */
-	src = zclient->ibuf;
-
-	stream_reset(src);
-
-	/* parse header */
-	ret = zclient_read_header(src, zclient->sock, &size, &marker, &version,
-				  &vrf_id, &resp_cmd);
-	if (ret < 0) {
-		if (errno != EAGAIN)
-			flog_err(EC_ZEBRA_LM_RESPONSE,
-				 "Error reading Label Manager response: %s",
-				 strerror(errno));
-		return -1;
-	}
-
-	/* do not relay a msg that has nothing to do with LM */
-	switch (resp_cmd) {
-	case ZEBRA_LABEL_MANAGER_CONNECT:
-	case ZEBRA_LABEL_MANAGER_CONNECT_ASYNC: /* should not be seen */
-	case ZEBRA_GET_LABEL_CHUNK:
-	case ZEBRA_RELEASE_LABEL_CHUNK:
-		break;
-	default:
-		zlog_debug("Not relaying '%s' response (size %d) from LM",
-			   zserv_command_string(resp_cmd), size);
-		return -1;
-	}
-
-	zlog_debug("Received '%s' response (size %d) from LM",
-		   zserv_command_string(resp_cmd), size);
-
-	if (size == 0)
-		return -1;
-
-	/* Get the 'proto' field of the message */
-	proto = stream_getc(src);
-
-	/* Get the 'instance' field of the message */
-	instance = stream_getw(src);
-
-	proto_str = zebra_route_string(proto);
-
-	/* lookup the client to relay the msg to */
-	zserv = zserv_find_client(proto, instance);
-	if (!zserv) {
-		flog_err(
-			EC_ZEBRA_LM_NO_SUCH_CLIENT,
-			"Error relaying LM response: can't find client %s, instance %u",
-			proto_str, instance);
-		return -1;
-	}
-	zlog_debug("Found client to relay LM response to client %s instance %u",
-		   proto_str, instance);
-
-	/* copy msg into output buffer */
-	dst = obuf;
-	stream_copy(dst, src);
-
-	/* send response back */
-	ret = writen(zserv->sock, dst->data, stream_get_endp(dst));
-	if (ret <= 0) {
-		flog_err(EC_ZEBRA_LM_RELAY_FAILED,
-			 "Error relaying LM response to %s instance %u: %s",
-			 proto_str, instance, strerror(errno));
-		return -1;
-	}
-	zlog_debug("Relayed LM response (%d bytes) to %s instance %u", ret,
-		   proto_str, instance);
-
-	return 0;
+	hook_call(lm_get_chunk, lmc, proto, instance, keep, size, base, vrf_id);
 }
-
-static int lm_zclient_read(struct thread *t)
-{
-	int ret;
-
-	zclient->t_read = NULL;
-
-	/* read response and send it back */
-	ret = relay_response_back();
-
-	/* re-arm read */
-	thread_add_read(zclient->master, lm_zclient_read, NULL,
-			zclient->sock, &zclient->t_read);
-	return ret;
-}
-
-static int reply_error(int cmd, struct zserv *zserv, vrf_id_t vrf_id)
+void lm_release_chunk_call(uint8_t proto, uint16_t instance, uint32_t start,
+			   uint32_t end)
 {
-	int ret;
-	struct stream *s;
-
-	s = stream_new(ZEBRA_MAX_PACKET_SIZ);
-
-	zclient_create_header(s, cmd, vrf_id);
-
-	/* proto */
-	stream_putc(s, zserv->proto);
-	/* instance */
-	stream_putw(s, zserv->instance);
-	/* result */
-	stream_putc(s, 1);
-
-	/* Write packet size. */
-	stream_putw_at(s, 0, stream_get_endp(s));
-
-	ret = writen(zserv->sock, s->data, stream_get_endp(s));
-
-	stream_free(s);
-	return ret;
-}
-/**
- * Receive a request to get or release a label chunk and forward it to external
- * label manager.
- *
- * It's called from zserv in case it's not an actual label manager, but just a
- * proxy.
- *
- * @param cmd Type of request (connect, get or release)
- * @param zserv
- * @return 0 on success, -1 otherwise
- */
-int zread_relay_label_manager_request(int cmd, struct zserv *zserv,
-				      struct stream *msg, vrf_id_t vrf_id)
-{
-	struct stream *dst;
-	int ret = 0;
-	uint8_t proto;
-	const char *proto_str;
-	unsigned short instance;
-
-	if (zclient->sock < 0) {
-		flog_err(EC_ZEBRA_LM_NO_SOCKET,
-			 "Unable to relay LM request: no socket");
-		reply_error(cmd, zserv, vrf_id);
-		return -1;
-	}
-
-	/* peek msg to get proto and instance id. This zebra, which acts as
-	 * a proxy needs to have such values for each client in order to
-	 * relay responses back to it.
-	 */
-
-	/* Get the 'proto' field of incoming msg */
-	proto = stream_getc(msg);
-
-	/* Get the 'instance' field of incoming msg */
-	instance = stream_getw(msg);
-
-	/* stringify proto */
-	proto_str = zebra_route_string(proto);
-
-	/* check & set client proto if unset */
-	if (zserv->proto && zserv->proto != proto) {
-		flog_warn(EC_ZEBRAING_LM_PROTO_MISMATCH,
-			  "Client proto(%u) != msg proto(%u)", zserv->proto,
-			  proto);
-		return -1;
-	}
-
-	/* check & set client instance if unset */
-	if (zserv->instance && zserv->instance != instance) {
-		flog_err(EC_ZEBRA_LM_BAD_INSTANCE,
-			 "Client instance(%u) != msg instance(%u)",
-			 zserv->instance, instance);
-		return -1;
-	}
-
-	/* recall proto and instance */
-	zserv->instance = instance;
-	zserv->proto = proto;
-
-	/* in case there's any incoming message enqueued, read and forward it */
-	if (zserv->is_synchronous)
-		while (ret == 0)
-			ret = relay_response_back();
-
-	/* get the msg buffer used toward the 'master' Label Manager */
-	dst = zclient->obuf;
-
-	/* copy the message */
-	stream_copy(dst, msg);
-
-	/* Send request to external label manager */
-	ret = writen(zclient->sock, dst->data, stream_get_endp(dst));
-	if (ret <= 0) {
-		flog_err(EC_ZEBRA_LM_RELAY_FAILED,
-			 "Error relaying LM request from %s instance %u: %s",
-			 proto_str, instance, strerror(errno));
-		reply_error(cmd, zserv, vrf_id);
-		return -1;
-	}
-	zlog_debug("Relayed LM request (%d bytes) from %s instance %u", ret,
-		   proto_str, instance);
-
-
-	/* Release label chunk has no response */
-	if (cmd == ZEBRA_RELEASE_LABEL_CHUNK)
-		return 0;
-
-	/* make sure we listen to the response */
-	if (!zclient->t_read)
-		thread_add_read(zclient->master, lm_zclient_read, NULL,
-				zclient->sock, &zclient->t_read);
-
-	return 0;
+	hook_call(lm_release_chunk, proto, instance, start, end);
 }
 
-static int lm_zclient_connect(struct thread *t)
-{
-	zclient->t_connect = NULL;
-
-	if (zclient->sock >= 0)
-		return 0;
-
-	if (zclient_socket_connect(zclient) < 0) {
-		flog_err(EC_ZEBRA_LM_CLIENT_CONNECTION_FAILED,
-			 "Error connecting synchronous zclient!");
-		thread_add_timer(zrouter.master, lm_zclient_connect, zclient,
-				 CONNECTION_DELAY, &zclient->t_connect);
-		return -1;
-	}
-
-	/* make socket non-blocking */
-	(void)set_nonblocking(zclient->sock);
-
-	return 0;
-}
+/* forward declarations of the static functions to be used for some hooks */
+static int label_manager_connect(uint8_t proto, uint16_t instance,
+				 vrf_id_t vrf_id);
+static int label_manager_disconnect(uint8_t proto, uint16_t instance);
+static int label_manager_get_chunk(struct label_manager_chunk **lmc,
+				   uint8_t proto, uint16_t instance,
+				   uint8_t keep, uint32_t size, uint32_t base,
+				   vrf_id_t vrf_id);
 
-/**
- * Function to initialize zclient in case this is not an actual
- * label manager, but just a proxy to an external one.
- *
- * @param lm_zserv_path Path to zserv socket of external label manager
- */
-static void lm_zclient_init(char *lm_zserv_path)
+void delete_label_chunk(void *val)
 {
-	if (lm_zserv_path)
-		frr_zclient_addr(&zclient_addr, &zclient_addr_len,
-				 lm_zserv_path);
-
-	/* Set default values. */
-	zclient = zclient_new(zrouter.master, &zclient_options_default);
-	zclient->privs = &zserv_privs;
-	zclient->sock = -1;
-	zclient->t_connect = NULL;
-	lm_zclient_connect(NULL);
+	XFREE(MTYPE_LM_CHUNK, val);
 }
 
 /**
@@ -339,15 +109,16 @@ static void lm_zclient_init(char *lm_zserv_path)
  * @param instance Instance, to identify the owner
  * @return Number of chunks released
  */
-int release_daemon_label_chunks(struct zserv *client)
+int release_daemon_label_chunks(uint8_t proto, unsigned short instance)
 {
-	uint8_t proto = client->proto;
-	uint16_t instance = client->instance;
 	struct listnode *node;
 	struct label_manager_chunk *lmc;
 	int count = 0;
 	int ret;
 
+	zlog_debug("%s: Releasing chunks for client proto %s, instance %d",
+		   __func__, zebra_route_string(proto), instance);
+
 	for (ALL_LIST_ELEMENTS_RO(lbl_mgr.lc_list, node, lmc)) {
 		if (lmc->proto == proto && lmc->instance == instance
 		    && lmc->keep == 0) {
@@ -363,33 +134,51 @@ int release_daemon_label_chunks(struct zserv *client)
 	return count;
 }
 
+int lm_client_disconnect_cb(struct zserv *client)
+{
+	uint8_t proto = client->proto;
+	uint16_t instance = client->instance;
+
+	hook_call(lm_client_disconnect, proto, instance);
+	return 0;
+}
+
+void lm_hooks_register(void)
+{
+	hook_register(lm_client_connect, label_manager_connect);
+	hook_register(lm_client_disconnect, label_manager_disconnect);
+	hook_register(lm_get_chunk, label_manager_get_chunk);
+	hook_register(lm_release_chunk, release_label_chunk);
+}
+void lm_hooks_unregister(void)
+{
+	hook_unregister(lm_client_connect, label_manager_connect);
+	hook_unregister(lm_client_disconnect, label_manager_disconnect);
+	hook_unregister(lm_get_chunk, label_manager_get_chunk);
+	hook_unregister(lm_release_chunk, release_label_chunk);
+}
+
 /**
  * Init label manager (or proxy to an external one)
  */
-void label_manager_init(char *lm_zserv_path)
+void label_manager_init(void)
 {
-	/* this is an actual label manager */
-	if (!lm_zserv_path) {
-		zlog_debug("Initializing internal label manager");
-		lm_is_external = false;
-		lbl_mgr.lc_list = list_new();
-		lbl_mgr.lc_list->del = delete_label_chunk;
-	} else { /* it's acting just as a proxy */
-		zlog_debug("Initializing external label manager at %s",
-			   lm_zserv_path);
-		lm_is_external = true;
-		lm_zclient_init(lm_zserv_path);
-	}
+	lbl_mgr.lc_list = list_new();
+	lbl_mgr.lc_list->del = delete_label_chunk;
+	hook_register(zserv_client_close, lm_client_disconnect_cb);
 
-	obuf = stream_new(ZEBRA_MAX_PACKET_SIZ);
+	/* register default hooks for the label manager actions */
+	lm_hooks_register();
 
-	hook_register(zserv_client_close, release_daemon_label_chunks);
+	/* notify any external module that we are done */
+	hook_call(lm_cbs_inited);
 }
 
 /* alloc and fill a label chunk */
-static struct label_manager_chunk *
-create_label_chunk(uint8_t proto, unsigned short instance, uint8_t keep,
-		   uint32_t start, uint32_t end)
+struct label_manager_chunk *create_label_chunk(uint8_t proto,
+					       unsigned short instance,
+					       uint8_t keep, uint32_t start,
+					       uint32_t end)
 {
 	/* alloc chunk, fill it and return it */
 	struct label_manager_chunk *lmc =
@@ -405,7 +194,7 @@ create_label_chunk(uint8_t proto, unsigned short instance, uint8_t keep,
 }
 
 /* attempt to get a specific label chunk */
-struct label_manager_chunk *
+static struct label_manager_chunk *
 assign_specific_label_chunk(uint8_t proto, unsigned short instance,
 			    uint8_t keep, uint32_t size, uint32_t base)
 {
@@ -607,9 +396,59 @@ int release_label_chunk(uint8_t proto, unsigned short instance, uint32_t start,
 	return ret;
 }
 
+/* default functions to be called on hooks  */
+static int label_manager_connect(uint8_t proto, uint16_t instance,
+				 vrf_id_t vrf_id)
+{
+	/*
+	 * Release previous labels of same protocol and instance.
+	 * This is done in case it restarted from an unexpected shutdown.
+	 */
+	release_daemon_label_chunks(proto, instance);
+	return lm_client_connect_response(proto, instance, vrf_id, 0);
+}
+static int label_manager_disconnect(uint8_t proto, uint16_t instance)
+{
+	release_daemon_label_chunks(proto, instance);
+	return 0;
+}
+static int label_manager_get_chunk(struct label_manager_chunk **lmc,
+				   uint8_t proto, uint16_t instance,
+				   uint8_t keep, uint32_t size, uint32_t base,
+				   vrf_id_t vrf_id)
+{
+	*lmc = assign_label_chunk(proto, instance, keep, size, base);
+	return lm_get_chunk_response(*lmc, proto, instance, vrf_id);
+}
+
+/* Respond to a connect request */
+int lm_client_connect_response(uint8_t proto, uint16_t instance,
+			       vrf_id_t vrf_id, uint8_t result)
+{
+	struct zserv *client = zserv_find_client(proto, instance);
+	if (!client) {
+		zlog_err("%s: could not find client for daemon %s instance %u",
+			 __func__, zebra_route_string(proto), instance);
+		return 1;
+	}
+	return zsend_label_manager_connect_response(client, vrf_id, result);
+}
+
+/* Respond to a get_chunk request */
+int lm_get_chunk_response(struct label_manager_chunk *lmc, uint8_t proto,
+			  uint16_t instance, vrf_id_t vrf_id)
+{
+	struct zserv *client = zserv_find_client(proto, instance);
+	if (!client) {
+		zlog_err("%s: could not find client for daemon %s instance %u",
+			 __func__, zebra_route_string(proto), instance);
+		return 1;
+	}
+	return zsend_assign_label_chunk_response(client, vrf_id, proto,
+						 instance, lmc);
+}
 
 void label_manager_close(void)
 {
 	list_delete(&lbl_mgr.lc_list);
-	stream_free(obuf);
 }
diff --git a/zebra/label_manager.h b/zebra/label_manager.h
index f1b7d050c..74e283e85 100644
--- a/zebra/label_manager.h
+++ b/zebra/label_manager.h
@@ -28,6 +28,7 @@
 
 #include "lib/linklist.h"
 #include "lib/thread.h"
+#include "lib/hook.h"
 
 #include "zebra/zserv.h"
 
@@ -57,6 +58,54 @@ struct label_manager_chunk {
 	uint32_t end;   /* Last label of the chunk */
 };
 
+/* declare hooks for the basic API, so that it can be specialized or served
+ * externally. Also declare a hook when those functions have been registered,
+ * so that any external module wanting to replace those can react
+ */
+
+DECLARE_HOOK(lm_client_connect,
+	     (uint8_t proto, uint16_t instance, vrf_id_t vrf_id),
+	     (proto, instance, vrf_id));
+DECLARE_HOOK(lm_client_disconnect, (uint8_t proto, uint16_t instance),
+	     (proto, instance));
+DECLARE_HOOK(lm_get_chunk,
+	     (struct label_manager_chunk * *lmc, uint8_t proto,
+	      uint16_t instance, uint8_t keep, uint32_t size, uint32_t base,
+	      vrf_id_t vrf_id),
+	     (lmc, proto, instance, keep, size, base, vrf_id));
+DECLARE_HOOK(lm_release_chunk,
+	     (uint8_t proto, uint16_t instance, uint32_t start, uint32_t end),
+	     (proto, instance, start, end));
+DECLARE_HOOK(lm_cbs_inited, (), ());
+
+
+/* declare wrappers to be called in zapi_msg.c (as hooks must be called in
+ * source file where they were defined)
+ */
+void lm_client_connect_call(uint8_t proto, uint16_t instance, vrf_id_t vrf_id);
+void lm_get_chunk_call(struct label_manager_chunk **lmc, uint8_t proto,
+		       uint16_t instance, uint8_t keep, uint32_t size,
+		       uint32_t base, vrf_id_t vrf_id);
+void lm_release_chunk_call(uint8_t proto, uint16_t instance, uint32_t start,
+			   uint32_t end);
+
+/* API for an external LM to return responses for requests */
+int lm_client_connect_response(uint8_t proto, uint16_t instance,
+			       vrf_id_t vrf_id, uint8_t result);
+int lm_get_chunk_response(struct label_manager_chunk *lmc, uint8_t proto,
+			  uint16_t instance, vrf_id_t vrf_id);
+
+/* convenience function to allocate an lmc to be consumed by the above API */
+struct label_manager_chunk *create_label_chunk(uint8_t proto,
+					       unsigned short instance,
+					       uint8_t keep, uint32_t start,
+					       uint32_t end);
+void delete_label_chunk(void *val);
+
+/* register/unregister callbacks for hooks */
+void lm_hooks_register(void);
+void lm_hooks_unregister(void);
+
 /*
  * Main label manager struct
  * Holds a linked list of label chunks.
@@ -65,18 +114,15 @@ struct label_manager {
 	struct list *lc_list;
 };
 
-bool lm_is_external;
-
-int zread_relay_label_manager_request(int cmd, struct zserv *zserv,
-				      struct stream *msg, vrf_id_t vrf_id);
-void label_manager_init(char *lm_zserv_path);
+void label_manager_init(void);
 struct label_manager_chunk *assign_label_chunk(uint8_t proto,
 					       unsigned short instance,
 					       uint8_t keep, uint32_t size,
 					       uint32_t base);
 int release_label_chunk(uint8_t proto, unsigned short instance, uint32_t start,
 			uint32_t end);
-int release_daemon_label_chunks(struct zserv *client);
+int lm_client_disconnect_cb(struct zserv *client);
+int release_daemon_label_chunks(uint8_t proto, unsigned short instance);
 void label_manager_close(void);
 
 #ifdef __cplusplus
diff --git a/zebra/main.c b/zebra/main.c
index 194710675..84e83bc37 100644
--- a/zebra/main.c
+++ b/zebra/main.c
@@ -92,7 +92,6 @@ struct option longopts[] = {
 	{"keep_kernel", no_argument, NULL, 'k'},
 	{"socket", required_argument, NULL, 'z'},
 	{"ecmp", required_argument, NULL, 'e'},
-	{"label_socket", no_argument, NULL, 'l'},
 	{"retain", no_argument, NULL, 'r'},
 	{"vrfdefaultname", required_argument, NULL, 'o'},
 	{"graceful_restart", required_argument, NULL, 'K'},
@@ -252,8 +251,6 @@ int main(int argc, char **argv)
 	// int batch_mode = 0;
 	char *zserv_path = NULL;
 	char *vrf_default_name_configured = NULL;
-	/* Socket to external label manager */
-	char *lblmgr_path = NULL;
 	struct sockaddr_storage dummy;
 	socklen_t dummylen;
 #if defined(HANDLE_ZAPI_FUZZING)
@@ -270,7 +267,7 @@ int main(int argc, char **argv)
 	frr_preinit(&zebra_di, argc, argv);
 
 	frr_opt_add(
-		"baz:e:l:o:rK:"
+		"baz:e:o:rK:"
 #ifdef HAVE_NETLINK
 		"s:n"
 #endif
@@ -286,7 +283,6 @@ int main(int argc, char **argv)
 		"  -a, --allow_delete       Allow other processes to delete zebra routes\n"
 		"  -z, --socket             Set path of zebra socket\n"
 		"  -e, --ecmp               Specify ECMP to use.\n"
-		"  -l, --label_socket       Socket to external label manager\n"
 		"  -r, --retain             When program terminates, retain added route by zebra.\n"
 		"  -o, --vrfdefaultname     Set default VRF name.\n"
 		"  -K, --graceful_restart   Graceful restart at the kernel level, timer in seconds for expiration\n"
@@ -341,9 +337,6 @@ int main(int argc, char **argv)
 				exit(1);
 			}
 			break;
-		case 'l':
-			lblmgr_path = optarg;
-			break;
 		case 'r':
 			retain_mode = 1;
 			break;
@@ -451,7 +444,7 @@ int main(int argc, char **argv)
 	zserv_start(zserv_path);
 
 	/* Init label manager */
-	label_manager_init(lblmgr_path);
+	label_manager_init();
 
 	/* RNH init */
 	zebra_rnh_init();
diff --git a/zebra/zapi_msg.c b/zebra/zapi_msg.c
index 198a47a21..e018b9595 100644
--- a/zebra/zapi_msg.c
+++ b/zebra/zapi_msg.c
@@ -57,7 +57,6 @@
 #include "zebra/rtadv.h"
 #include "zebra/zebra_mpls.h"
 #include "zebra/zebra_mroute.h"
-#include "zebra/label_manager.h"
 #include "zebra/zebra_vxlan.h"
 #include "zebra/rt.h"
 #include "zebra/zebra_pbr.h"
@@ -928,10 +927,9 @@ int zsend_pw_update(struct zserv *client, struct zebra_pw *pw)
 }
 
 /* Send response to a get label chunk request to client */
-static int zsend_assign_label_chunk_response(struct zserv *client,
-					     vrf_id_t vrf_id, uint8_t proto,
-					     uint16_t instance,
-					     struct label_manager_chunk *lmc)
+int zsend_assign_label_chunk_response(struct zserv *client, vrf_id_t vrf_id,
+				      uint8_t proto, uint16_t instance,
+				      struct label_manager_chunk *lmc)
 {
 	int ret;
 	struct stream *s = stream_new(ZEBRA_MAX_PACKET_SIZ);
@@ -959,9 +957,8 @@ static int zsend_assign_label_chunk_response(struct zserv *client,
 }
 
 /* Send response to a label manager connect request to client */
-static int zsend_label_manager_connect_response(struct zserv *client,
-						vrf_id_t vrf_id,
-						unsigned short result)
+int zsend_label_manager_connect_response(struct zserv *client, vrf_id_t vrf_id,
+					 unsigned short result)
 {
 	int ret;
 	struct stream *s = stream_new(ZEBRA_MAX_PACKET_SIZ);
@@ -1897,27 +1894,16 @@ static void zread_label_manager_connect(struct zserv *client,
 		flog_err(EC_ZEBRA_TM_WRONG_PROTO,
 			 "client %d has wrong protocol %s", client->sock,
 			 zebra_route_string(proto));
-		if (client->is_synchronous)
-			zsend_label_manager_connect_response(client, vrf_id, 1);
+		zsend_label_manager_connect_response(client, vrf_id, 1);
 		return;
 	}
-	zlog_notice("client %d with vrf %u instance %u connected as %s",
-		    client->sock, vrf_id, instance, zebra_route_string(proto));
+
+	/* recall proto and instance in this socket */
 	client->proto = proto;
 	client->instance = instance;
 
-	/*
-	 * Release previous labels of same protocol and instance.
-	 * This is done in case it restarted from an unexpected shutdown.
-	 */
-	release_daemon_label_chunks(client);
-
-	zlog_debug(
-		" Label Manager client connected: sock %d, proto %s, vrf %u instance %u",
-		client->sock, zebra_route_string(proto), vrf_id, instance);
-	/* send response back */
-	if (client->is_synchronous)
-		zsend_label_manager_connect_response(client, vrf_id, 0);
+	/* call hook for connection using wrapper */
+	lm_client_connect_call(proto, instance, vrf_id);
 
 stream_failure:
 	return;
@@ -1929,7 +1915,7 @@ static void zread_get_label_chunk(struct zserv *client, struct stream *msg,
 	struct stream *s;
 	uint8_t keep;
 	uint32_t size, base;
-	struct label_manager_chunk *lmc;
+	struct label_manager_chunk *lmc = NULL;
 	uint8_t proto;
 	unsigned short instance;
 
@@ -1943,7 +1929,9 @@ static void zread_get_label_chunk(struct zserv *client, struct stream *msg,
 	STREAM_GETL(s, size);
 	STREAM_GETL(s, base);
 
-	lmc = assign_label_chunk(proto, instance, keep, size, base);
+	/* call hook to get a chunk using wrapper */
+	lm_get_chunk_call(&lmc, proto, instance, keep, size, base, vrf_id);
+
 	if (!lmc)
 		flog_err(
 			EC_ZEBRA_LM_CANNOT_ASSIGN_CHUNK,
@@ -1953,8 +1941,6 @@ static void zread_get_label_chunk(struct zserv *client, struct stream *msg,
 		zlog_debug("Assigned Label Chunk %u - %u to %s instance %u",
 			   lmc->start, lmc->end,
 			   zebra_route_string(proto), instance);
-	/* send response back */
-	zsend_assign_label_chunk_response(client, vrf_id, proto, instance, lmc);
 
 stream_failure:
 	return;
@@ -1976,33 +1962,23 @@ static void zread_release_label_chunk(struct zserv *client, struct stream *msg)
 	STREAM_GETL(s, start);
 	STREAM_GETL(s, end);
 
-	release_label_chunk(proto, instance, start, end);
+	/* call hook to release a chunk using wrapper */
+	lm_release_chunk_call(proto, instance, start, end);
 
 stream_failure:
 	return;
 }
+
 static void zread_label_manager_request(ZAPI_HANDLER_ARGS)
 {
-	/* to avoid sending other messages like ZERBA_INTERFACE_UP */
-	client->is_synchronous = hdr->command ==
-				 ZEBRA_LABEL_MANAGER_CONNECT;
-
-	/* external label manager */
-	if (lm_is_external)
-		zread_relay_label_manager_request(hdr->command, client, msg,
-						  zvrf_id(zvrf));
-	/* this is a label manager */
+	if (hdr->command == ZEBRA_LABEL_MANAGER_CONNECT
+	    || hdr->command == ZEBRA_LABEL_MANAGER_CONNECT_ASYNC)
+		zread_label_manager_connect(client, msg, zvrf_id(zvrf));
 	else {
-		if (hdr->command == ZEBRA_LABEL_MANAGER_CONNECT ||
-		    hdr->command == ZEBRA_LABEL_MANAGER_CONNECT_ASYNC)
-			zread_label_manager_connect(client, msg, zvrf_id(zvrf));
-		else {
-			if (hdr->command == ZEBRA_GET_LABEL_CHUNK)
-				zread_get_label_chunk(client, msg,
-						      zvrf_id(zvrf));
-			else if (hdr->command == ZEBRA_RELEASE_LABEL_CHUNK)
-				zread_release_label_chunk(client, msg);
-		}
+		if (hdr->command == ZEBRA_GET_LABEL_CHUNK)
+			zread_get_label_chunk(client, msg, zvrf_id(zvrf));
+		else if (hdr->command == ZEBRA_RELEASE_LABEL_CHUNK)
+			zread_release_label_chunk(client, msg);
 	}
 }
 
diff --git a/zebra/zapi_msg.h b/zebra/zapi_msg.h
index d30fa2d0e..884edfef0 100644
--- a/zebra/zapi_msg.h
+++ b/zebra/zapi_msg.h
@@ -29,6 +29,8 @@
 #include "zebra/zserv.h"
 #include "zebra/zebra_pbr.h"
 #include "zebra/zebra_errors.h"
+#include "zebra/label_manager.h"
+
 
 #ifdef __cplusplus
 extern "C" {
@@ -90,6 +92,14 @@ extern void zserv_nexthop_num_warn(const char *caller, const struct prefix *p,
 				   const unsigned int nexthop_num);
 
 extern void zsend_capabilities_all_clients(void);
+extern int zsend_assign_label_chunk_response(struct zserv *client,
+					     vrf_id_t vrf_id, uint8_t proto,
+					     uint16_t instance,
+					     struct label_manager_chunk *lmc);
+extern int zsend_label_manager_connect_response(struct zserv *client,
+						vrf_id_t vrf_id,
+						unsigned short result);
+
 
 #ifdef __cplusplus
 }
diff --git a/zebra/zserv.c b/zebra/zserv.c
index cb9ca6578..70b459481 100644
--- a/zebra/zserv.c
+++ b/zebra/zserv.c
@@ -535,28 +535,6 @@ static int zserv_process_messages(struct thread *thread)
 
 int zserv_send_message(struct zserv *client, struct stream *msg)
 {
-	/*
-	 * This is a somewhat poorly named variable added with Zebra's portion
-	 * of the label manager. That component does not use the regular
-	 * zserv/zapi_msg interface for handling its messages, as the client
-	 * itself runs in-process. Instead it uses synchronous writes on the
-	 * zserv client's socket directly in the zread* handlers for its
-	 * message types. Furthermore, it cannot handle the usual messages
-	 * Zebra sends (such as those for interface changes) and so has added
-	 * this flag and check here as a hack to suppress all messages that it
-	 * does not explicitly know about.
-	 *
-	 * In any case this needs to be cleaned up at some point.
-	 *
-	 * See also:
-	 *    zread_label_manager_request
-	 *    zsend_label_manager_connect_response
-	 *    zsend_assign_label_chunk_response
-	 *    ...
-	 */
-	if (client->is_synchronous)
-		return 0;
-
 	pthread_mutex_lock(&client->obuf_mtx);
 	{
 		stream_fifo_push(client->obuf_fifo, msg);
@@ -710,9 +688,6 @@ static struct zserv *zserv_client_create(int sock)
 	}
 	client->ridinfo = vrf_bitmap_init();
 
-	/* by default, it's not a synchronous client */
-	client->is_synchronous = 0;
-
 	/* Add this client to linked list. */
 	listnode_add(zrouter.client_list, client);
 
diff --git a/zebra/zserv.h b/zebra/zserv.h
index 34965618f..708ff1e22 100644
--- a/zebra/zserv.h
+++ b/zebra/zserv.h
@@ -98,7 +98,6 @@ struct zserv {
 	/* client's protocol */
 	uint8_t proto;
 	uint16_t instance;
-	uint8_t is_synchronous;
 
 	/* Statistics */
 	uint32_t redist_v4_add_cnt;