zebra: Add handling for kernel del/update nexthop

Add handling for delete/update nexthop object messages from the
kernel.

If someone deletes a nexthop object we are still using, send it back
down. If the someone updates a nexthop we are using, replace that nexthop
with ours. Routes are referencing this nexthop object ID and we resolved
it ourselves, so we should force the other `someone` to submit to our
will.

Signed-off-by: Stephen Worley <sworley@cumulusnetworks.com>

zebra/rt_netlink.c

@@ -1942,6 +1942,10 @@ static int netlink_nexthop(int cmd, struct zebra_dplane_ctx *ctx)
 
 	req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct nhmsg));
 	req.n.nlmsg_flags = NLM_F_CREATE | NLM_F_REQUEST;
+
+	if (cmd == RTM_NEWNEXTHOP)
+		req.n.nlmsg_flags |= NLM_F_REPLACE;
+
 	req.n.nlmsg_type = cmd;
 	req.n.nlmsg_pid = dplane_ctx_get_ns(ctx)->nls.snl.nl_pid;
 
@@ -2287,11 +2291,8 @@ int netlink_nexthop_change(struct nlmsghdr *h, ns_id_t ns_id, int startup)
 	struct nh_grp grp[MULTIPATH_NUM] = {};
 	/* Count of nexthops in group array */
 	uint8_t grp_count = 0;
-	/* struct that goes into our tables */
-	struct nhg_hash_entry *nhe = NULL;
 	struct rtattr *tb[NHA_MAX + 1] = {};
 
-
 	nhm = NLMSG_DATA(h);
 
 	if (startup && h->nlmsg_type != RTM_NEWNEXTHOP)
@@ -2367,41 +2368,12 @@ int netlink_nexthop_change(struct nlmsghdr *h, ns_id_t ns_id, int startup)
 			vrf_id = nh.vrf_id;
 		}
 
-		// TODO: Apparently we don't want changes
-		// to already created one in our table.
-		// They should be immutable...
-		// Gotta figure that one out.
-
-
 		if (zebra_nhg_kernel_find(id, &nh, grp, grp_count, vrf_id, afi,
 					  type, startup))
 			return -1;
 
-
+	} else if (h->nlmsg_type == RTM_DELNEXTHOP)
-	} else if (h->nlmsg_type == RTM_DELNEXTHOP) {
+		zebra_nhg_kernel_del(id);
-		// TODO: Add new function in nhgc to handle del
-		nhe = zebra_nhg_lookup_id(id);
-		if (!nhe) {
-			flog_warn(
-				EC_ZEBRA_BAD_NHG_MESSAGE,
-				"Kernel delete message received for nexthop group ID (%u) that we do not have in our ID table",
-				id);
-			return -1;
-		}
-
-		zebra_nhg_set_invalid(nhe);
-
-		// TODO: Probably won't need this if we expect
-		// upper level protocol to fix it.
-		if (nhe->refcnt) {
-			flog_err(
-				EC_ZEBRA_NHG_SYNC,
-				"Kernel deleted a nexthop group with ID (%u) that we are still using for a route, sending it back down",
-				nhe->id);
-			zebra_nhg_install_kernel(nhe);
-		} else
-			zebra_nhg_set_invalid(nhe);
-	}
 
 	return 0;
 }

zebra/zebra_nhg.c

@@ -458,7 +458,7 @@ static bool zebra_nhg_find(struct nhg_hash_entry **nhe, uint32_t id,
 
 	lookup.afi = afi;
 	lookup.vrf_id = vrf_id;
-	lookup.type = type;
+	lookup.type = type ? type : ZEBRA_ROUTE_NHG;
 	lookup.nhg = nhg;
 
 	if (nhg_depends)
@@ -576,12 +576,78 @@ static void zebra_nhg_set_dup(struct nhg_hash_entry *nhe)
 		  nhe->id);
 }
 
+/*
+ * Release from the non-ID hash'd table.
+ *
+ * Basically, we are saying don't let routes use this anymore,
+ * because we are removing it.
+ */
+static void zebra_nhg_release_no_id(struct nhg_hash_entry *nhe)
+{
+	/* Remove it from any lists it may be on */
+	zebra_nhg_depends_release(nhe);
+	zebra_nhg_dependents_release(nhe);
+	if (nhe->ifp)
+		if_nhg_dependents_del(nhe->ifp, nhe);
+
+	/*
+	 * If its a dup, we didn't store it here and have to be
+	 * sure we don't clear one thats actually being used.
+	 */
+	if (!CHECK_FLAG(nhe->flags, NEXTHOP_GROUP_DUPLICATE))
+		hash_release(zrouter.nhgs, nhe);
+}
+
+static void zebra_nhg_release_id(struct nhg_hash_entry *nhe)
+{
+	hash_release(zrouter.nhgs_id, nhe);
+}
+
+
+static void zebra_nhg_handle_uninstall(struct nhg_hash_entry *nhe)
+{
+	zebra_nhg_release_id(nhe);
+	zebra_nhg_free(nhe);
+}
+
+/*
+ * The kernel/other program has changed the state of a nexthop object we are
+ * using.
+ */
+static void zebra_nhg_handle_kernel_state_change(struct nhg_hash_entry *nhe,
+						 bool is_delete)
+{
+	if (nhe->refcnt) {
+		flog_err(
+			EC_ZEBRA_NHG_SYNC,
+			"Kernel %s a nexthop group with ID (%u) that we are still using for a route, sending it back down",
+			(is_delete ? "deleted" : "updated"), nhe->id);
+
+		UNSET_FLAG(nhe->flags, NEXTHOP_GROUP_INSTALLED);
+		zebra_nhg_install_kernel(nhe);
+	} else {
+		zebra_nhg_release_no_id(nhe);
+		zebra_nhg_handle_uninstall(nhe);
+	}
+}
+
 static int nhg_ctx_process_new(struct nhg_ctx *ctx)
 {
 	struct nexthop_group *nhg = NULL;
 	struct nhg_connected_tree_head nhg_depends = {};
+	struct nhg_hash_entry *lookup = NULL;
 	struct nhg_hash_entry *nhe = NULL;
 
+	lookup = zebra_nhg_lookup_id(ctx->id);
+
+	if (lookup) {
+		/* This is already present in our table, hence an update
+		 * that we did not initate.
+		 */
+		zebra_nhg_handle_kernel_state_change(lookup, false);
+		return 0;
+	}
+
 	if (ctx->count) {
 		nhg = nexthop_group_new();
 		zebra_nhg_process_grp(nhg, &nhg_depends, ctx->u.grp,
@@ -640,6 +706,25 @@ static int nhg_ctx_process_new(struct nhg_ctx *ctx)
 	return 0;
 }
 
+static int nhg_ctx_process_del(struct nhg_ctx *ctx)
+{
+	struct nhg_hash_entry *nhe = NULL;
+
+	nhe = zebra_nhg_lookup_id(ctx->id);
+
+	if (!nhe) {
+		flog_warn(
+			EC_ZEBRA_BAD_NHG_MESSAGE,
+			"Kernel delete message received for nexthop group ID (%u) that we do not have in our ID table",
+			ctx->id);
+		return 0;
+	}
+
+	zebra_nhg_handle_kernel_state_change(nhe, true);
+
+	return 0;
+}
+
 static void nhg_ctx_process_finish(struct nhg_ctx *ctx)
 {
 	/*
@@ -660,6 +745,7 @@ int nhg_ctx_process(struct nhg_ctx *ctx)
 		ret = nhg_ctx_process_new(ctx);
 		break;
 	case NHG_CTX_OP_DEL:
+		ret = nhg_ctx_process_del(ctx);
 	case NHG_CTX_OP_NONE:
 		break;
 	}
@@ -692,11 +778,6 @@ int zebra_nhg_kernel_find(uint32_t id, struct nexthop *nh, struct nh_grp *grp,
 			  uint8_t count, vrf_id_t vrf_id, afi_t afi, int type,
 			  int startup)
 {
-	// TODO: Can probably put table lookup
-	// here before queueing? And if deleted, re-send to kernel?
-	// ... Well, if changing the flags it probably needs to be queued
-	// still...
-
 	struct nhg_ctx *ctx = NULL;
 
 	if (id > id_counter)
@@ -736,6 +817,25 @@ int zebra_nhg_kernel_find(uint32_t id, struct nexthop *nh, struct nh_grp *grp,
 	return 0;
 }
 
+/* Kernel-side, received delete message */
+int zebra_nhg_kernel_del(uint32_t id)
+{
+	struct nhg_ctx *ctx = NULL;
+
+	ctx = nhg_ctx_new();
+
+	ctx->id = id;
+
+	nhg_ctx_set_op(ctx, NHG_CTX_OP_DEL);
+
+	if (queue_add(ctx)) {
+		nhg_ctx_process_finish(ctx);
+		return -1;
+	}
+
+	return 0;
+}
+
 /* Some dependency helper functions */
 static struct nhg_hash_entry *depends_find(struct nexthop *nh, afi_t afi)
 {
@@ -862,33 +962,6 @@ void zebra_nhg_free(void *arg)
 	XFREE(MTYPE_NHG, nhe);
 }
 
-/*
- * Release from the non-ID hash'd table.
- *
- * Basically, we are saying don't let routes use this anymore,
- * because we are removing it.
- */
-static void zebra_nhg_release_no_id(struct nhg_hash_entry *nhe)
-{
-	/* Remove it from any lists it may be on */
-	zebra_nhg_depends_release(nhe);
-	zebra_nhg_dependents_release(nhe);
-	if (nhe->ifp)
-		if_nhg_dependents_del(nhe->ifp, nhe);
-
-	/*
-	 * If its a dup, we didn't store it here and have to be
-	 * sure we don't clear one thats actually being used.
-	 */
-	if (!CHECK_FLAG(nhe->flags, NEXTHOP_GROUP_DUPLICATE))
-		hash_release(zrouter.nhgs, nhe);
-}
-
-static void zebra_nhg_release_id(struct nhg_hash_entry *nhe)
-{
-	hash_release(zrouter.nhgs_id, nhe);
-}
-
 void zebra_nhg_decrement_ref(struct nhg_hash_entry *nhe)
 {
 	nhe->refcnt--;
@@ -1627,13 +1700,6 @@ void zebra_nhg_install_kernel(struct nhg_hash_entry *nhe)
 	}
 }
 
-static void zebra_nhg_handle_uninstall(struct nhg_hash_entry *nhe)
-{
-	zlog_debug("Freeing nhe_id=%u", nhe->id);
-	zebra_nhg_release_id(nhe);
-	zebra_nhg_free(nhe);
-}
-
 void zebra_nhg_uninstall_kernel(struct nhg_hash_entry *nhe)
 {
 	/* Release from the non-ID hash'd table so nothing tries to use it */
@@ -1642,6 +1708,8 @@ void zebra_nhg_uninstall_kernel(struct nhg_hash_entry *nhe)
 	if (CHECK_FLAG(nhe->flags, NEXTHOP_GROUP_INSTALLED)) {
 		int ret = dplane_nexthop_delete(nhe);
 
+		/* Change its type to us since we are installing it */
+		nhe->type = ZEBRA_ROUTE_NHG;
 		switch (ret) {
 		case ZEBRA_DPLANE_REQUEST_QUEUED:
 			SET_FLAG(nhe->flags, NEXTHOP_GROUP_QUEUED);

zebra/zebra_nhg.h

@@ -230,6 +230,8 @@ extern int zebra_nhg_kernel_find(uint32_t id, struct nexthop *nh,
 				 struct nh_grp *grp, uint8_t count,
 				 vrf_id_t vrf_id, afi_t afi, int type,
 				 int startup);
+/* Del via kernel */
+extern int zebra_nhg_kernel_del(uint32_t id);
 
 /* Find via route creation */
 extern struct nhg_hash_entry *