Init: handle reconfiguration

With this change, init becomes able to respond to config changes by
restarting the scenario with the new config. To make this feature useful
in practice, init must not fail under any circumstances. Even on
conditions that were considered as fatal previously and led to the abort
of init (such as ambiguous names of the children or misconfiguration in
general), init must stay alive and responsive to config changes.

os/include/init/child.h

@@ -295,6 +295,13 @@ namespace Init {
 
 	class Child : Genode::Child_policy
 	{
+		public:
+
+			/**
+			 * Exception type
+			 */
+			class Child_name_is_not_unique { };
+
 		private:
 
 			friend class Child_registry;
@@ -334,7 +341,6 @@ namespace Init {
 					/* check for a name confict with the other children */
 					if (!registry->is_unique(unique)) {
 						PERR("Child name \"%s\" is not unique", unique);
-						class Child_name_is_not_unique { };
 						throw Child_name_is_not_unique();
 					}
 

os/run/ldso.run

@@ -29,7 +29,7 @@ append qemu_args "-nographic -m 64"
 run_genode_until "child exited with exit value 0.*\n" 10
 
 # pay only attention to the output of init and its children
-grep_output {^\[init}
+grep_output {^\[init }
 
 unify_output {environ: [a-f0-9]+} "environ: <unified>"
 
@@ -54,6 +54,5 @@ compare_output_to {
 	[init -> test-ldso] Libc test: abs(-10): 10
 	[init -> test-ldso] ================
 	[init -> test-ldso] 
-	[init] virtual void Genode::Child_policy::exit(int): child exited with exit value 0
 }
 

os/run/tar_rom.run

@@ -35,6 +35,7 @@ install_config {
 		<service name="RM"/>
 		<service name="CPU"/>
 		<service name="LOG"/>
+		<service name="SIGNAL"/>
 	</parent-provides>
 	<default-route>
 		<any-service> <parent/> <any-child/> </any-service>

os/src/init/main.cc

@@ -89,15 +89,32 @@ namespace Init {
 				Child_list::insert(&child->_list_element);
 			}
 
+			/**
+			 * Unregister child
+			 */
+			void remove(Child *child)
+			{
+				Child_list::remove(&child->_list_element);
+			}
+
 			/**
 			 * Start execution of all children
 			 */
-			void start() {
+			void start()
+			{
 				Genode::List_element<Child> *curr = first();
 				for (; curr; curr = curr->next())
 					curr->object()->start();
 			}
 
+			/**
+			 * Return any of the registered children, or 0 if no child exists
+			 */
+			Child *any()
+			{
+				return first() ? first()->object() : 0;
+			}
+
 
 			/*****************************
 			 ** Name-registry interface **
@@ -129,54 +146,97 @@ namespace Init {
 int main(int, char **)
 {
 	using namespace Init;
-
-	try {
-		config_verbose =
-			Genode::config()->xml_node().attribute("verbose").has_value("yes"); }
-	catch (...) { }
+	using namespace Genode;
 
 	/* look for dynamic linker */
 	try {
-		static Genode::Rom_connection rom("ld.lib.so");
-		Genode::Process::dynamic_linker(rom.dataspace());
+		static Rom_connection rom("ld.lib.so");
+		Process::dynamic_linker(rom.dataspace());
 	} catch (...) { }
 
-	static Genode::Service_registry parent_services;
-	static Genode::Service_registry child_services;
-	static Child_registry           children;
-	static Genode::Cap_connection   cap;
+	static Service_registry parent_services;
+	static Service_registry child_services;
+	static Child_registry   children;
+	static Cap_connection   cap;
 
-	try { determine_parent_services(&parent_services); }
-	catch (...) { }
+	/*
+	 * Signal receiver for config changes
+	 */
+	Signal_receiver sig_rec;
+	Signal_context  sig_ctx;
+	config()->sigh(sig_rec.manage(&sig_ctx));
 
-	/* determine default route for resolving service requests */
-	Genode::Xml_node default_route_node("<empty/>");
-	try {
-		default_route_node =
-			Genode::config()->xml_node().sub_node("default-route"); }
-	catch (...) { }
+	for (;;) {
 
-	/* create children */
-	try {
-		Genode::Xml_node start_node = Genode::config()->xml_node().sub_node("start");
-		for (;; start_node = start_node.next("start")) {
+		try {
+			config_verbose =
+				config()->xml_node().attribute("verbose").has_value("yes"); }
+		catch (...) { }
 
-			children.insert(new (Genode::env()->heap())
-			                Child(start_node, default_route_node, &children,
-			                      read_prio_levels_log2(),
-			                      &parent_services, &child_services, &cap));
+		try { determine_parent_services(&parent_services); }
+		catch (...) { }
 
-			if (start_node.is_last("start")) break;
+		/* determine default route for resolving service requests */
+		Xml_node default_route_node("<empty/>");
+		try {
+			default_route_node =
+			config()->xml_node().sub_node("default-route"); }
+		catch (...) { }
+
+		/* create children */
+		try {
+			Xml_node start_node = config()->xml_node().sub_node("start");
+			for (;; start_node = start_node.next("start")) {
+
+				try {
+					children.insert(new (env()->heap())
+					                Init::Child(start_node, default_route_node,
+					                &children, read_prio_levels_log2(),
+					                &parent_services, &child_services, &cap));
+				}
+				catch (Rom_connection::Rom_connection_failed) {
+					/*
+					 * The binary does not exist. An error message is printed
+					 * by the Rom_connection constructor.
+					 */
+				}
+
+				if (start_node.is_last("start")) break;
+			}
+
+			/* start children */
+			children.start();
 		}
-	}
-	catch (Genode::Xml_node::Nonexistent_sub_node) {
-		PERR("No children to start");
+		catch (Xml_node::Nonexistent_sub_node) {
+			PERR("No children to start"); }
+		catch (Config::Invalid) {
+			PERR("No valid config found"); }
+		catch (Init::Child::Child_name_is_not_unique) { }
+
+		/*
+		 * Respond to config changes at runtime
+		 *
+		 * If the config gets updated to a new version, we kill the current
+		 * scenario and start again with the new config.
+		 */
+
+		/* wait for config change */
+		sig_rec.wait_for_signal();
+
+		/* kill all currently running children */
+		while (children.any()) {
+			Init::Child *child = children.any();
+			children.remove(child);
+			destroy(env()->heap(), child);
+		}
+
+		/* reset knowledge about parent services */
+		parent_services.remove_all();
+
+		/* reload config */
+		config()->reload();
 	}
 
-	/* start children */
-	children.start();
-
-	Genode::sleep_forever();
 	return 0;
 }
 

os/src/init/target.mk

@@ -1,3 +1,3 @@
 TARGET = init
 SRC_CC = main.cc
-LIBS   = env cxx server child init_pd_args
+LIBS   = env cxx server child init_pd_args signal