lifecycle: add lif_lifecycle_count_rdepends(), which calculates reverse dependency depth

cmd/ifquery.c

@@ -290,6 +290,12 @@ ifquery_main(int argc, char *argv[])
 		return EXIT_FAILURE;
 	}
 
+	if (!lif_lifecycle_count_rdepends(&exec_opts, &collection))
+	{
+		fprintf(stderr, "%s: could not validate dependency tree\n", argv0);
+		return EXIT_FAILURE;
+	}
+
 	/* --list --state is not allowed */
 	if (listing && listing_stat)
 		generic_usage(self_applet, EXIT_FAILURE);

cmd/ifupdown.c

@@ -229,6 +229,12 @@ ifupdown_main(int argc, char *argv[])
 		return EXIT_FAILURE;
 	}
 
+	if (!lif_lifecycle_count_rdepends(&exec_opts, &collection))
+	{
+		fprintf(stderr, "%s: could not validate dependency tree\n", argv0);
+		return EXIT_FAILURE;
+	}
+
 	if (!lif_state_sync(&state, &collection))
 	{
 		fprintf(stderr, "%s: could not sync state\n", argv0);

libifupdown/lifecycle.c

@@ -389,3 +389,58 @@ lif_lifecycle_run(const struct lif_execute_opts *opts, struct lif_interface *ifa
 
 	return true;
 }
+
+static bool
+count_interface_rdepends(const struct lif_execute_opts *opts, struct lif_dict *collection, struct lif_interface *parent, size_t depth)
+{
+	/* query our dependents if we don't have them already */
+	if (!lif_lifecycle_query_dependents(opts, parent, parent->ifname))
+		return false;
+
+	/* set rdepends_count to depth, dependents will be depth + 1 */
+	parent->rdepends_count = depth;
+
+	struct lif_dict_entry *requires = lif_dict_find(&parent->vars, "requires");
+
+	/* no dependents, nothing to worry about */
+	if (requires == NULL)
+		return true;
+
+	/* walk any dependents */
+	char require_ifs[4096] = {};
+	strlcpy(require_ifs, requires->data, sizeof require_ifs);
+	char *bufp = require_ifs;
+
+	for (char *tokenp = lif_next_token(&bufp); *tokenp; tokenp = lif_next_token(&bufp))
+	{
+		struct lif_interface *iface = lif_interface_collection_find(collection, tokenp);
+
+		if (!count_interface_rdepends(opts, collection, iface, depth + 1))
+			return false;
+	}
+
+	return true;
+}
+
+bool
+lif_lifecycle_count_rdepends(const struct lif_execute_opts *opts, struct lif_dict *collection)
+{
+	struct lif_node *iter;
+
+	LIF_DICT_FOREACH(iter, collection)
+	{
+		struct lif_dict_entry *entry = iter->data;
+		struct lif_interface *iface = entry->data;
+
+		/* start depth at interface's rdepends_count, which will be 0 for the root,
+		 * but will be more if additional rdepends are found...
+		 */
+		if (!count_interface_rdepends(opts, collection, iface, iface->rdepends_count))
+		{
+			fprintf(stderr, "ifupdown: dependency graph is broken for interface %s\n", iface->ifname);
+			return false;
+		}
+	}
+
+	return true;
+}

libifupdown/lifecycle.h

@@ -22,6 +22,7 @@
 extern bool lif_lifecycle_query_dependents(const struct lif_execute_opts *opts, struct lif_interface *iface, const char *lifname);
 extern bool lif_lifecycle_run_phase(const struct lif_execute_opts *opts, struct lif_interface *iface, const char *phase, const char *lifname, bool up);
 extern bool lif_lifecycle_run(const struct lif_execute_opts *opts, struct lif_interface *iface, struct lif_dict *collection, struct lif_dict *state, const char *lifname, bool up);
+extern bool lif_lifecycle_count_rdepends(const struct lif_execute_opts *opts, struct lif_dict *collection);
 
 #endif