Omit child-name prefix in <if-args> check

When matching the 'label' session argument using '<if-args>' in a
routing table, we can omit the child name prefix because it is always
the same for all sessions originating from the child anyway. Therefore,
this patch adds a special case for matching session labels. It makes the
expression of label-specific routing more intuitive.

os/include/init/child.h

@@ -96,11 +96,47 @@ namespace Init {
 	}
 
 
+	/**
+	 * Return sub string of label with the leading child name stripped out
+	 *
+	 */
+	inline char const *skip_label_prefix(char const *child_name, char const *label)
+	{
+		Genode::size_t const child_name_len = Genode::strlen(child_name);
+
+		/*
+		 * If the function was called with a valid "label" string, the
+		 * following condition should be always satisfied. See the
+		 * comment in 'service_node_args_condition_satisfied'.
+		 */
+		if (Genode::strcmp(child_name, label, child_name_len) == 0)
+			label += child_name_len;
+
+		/*
+		 * If the original label was empty, the 'Child_policy_enforce_labeling'
+		 * does not append a label separator after the child-name prefix. In
+		 * this case, we resulting label is empty.
+		 */
+		if (*label == 0)
+			return label;
+
+		/*
+		 * Skip label separator. This condition should be always satisfied.
+		 */
+		if (Genode::strcmp(" -> ", label, 4) == 0)
+			return label + 4;
+
+		PWRN("cannot skip label prefix while processing <if-arg>");
+		return label;
+	}
+
+
 	/**
 	 * Check if arguments satisfy the condition specified for the route
 	 */
 	inline bool service_node_args_condition_satisfied(Genode::Xml_node service_node,
-	                                                  const char *args)
+	                                                  const char *args,
+	                                                  char const *child_name)
 	{
 		try {
 			Genode::Xml_node if_arg = service_node.sub_node("if-arg");
@@ -112,6 +148,23 @@ namespace Init {
 
 			char arg_value[VALUE_MAX_LEN];
 			Genode::Arg_string::find_arg(args, key).string(arg_value, sizeof(arg_value), "");
+
+			PDBG("key='%s' value='%s' arg_value='%s'", key, value, arg_value);
+
+			/*
+			 * Skip child-name prefix if the key is the process "label".
+			 *
+			 * Because 'filter_session_args' is called prior the call of
+			 * 'resolve_session_request' from the 'Child::session' function,
+			 * 'args' contains the filtered arguments, in particular the label
+			 * prefixed with the child's name. For the 'if-args' declaration,
+			 * however, we want to omit specifying this prefix because the
+			 * session route is specific to the named start node anyway. So
+			 * the prefix information is redundant.
+			 */
+			if (Genode::strcmp("label", key) == 0)
+				return Genode::strcmp(value, skip_label_prefix(child_name, arg_value)) == 0;
+
 			return Genode::strcmp(value, arg_value) == 0;
 		} catch (...) { }
 
@@ -492,7 +545,7 @@ namespace Init {
 						if (!service_node_matches(service_node, service_name))
 							continue;
 
-						if (!service_node_args_condition_satisfied(service_node, args))
+						if (!service_node_args_condition_satisfied(service_node, args, name()))
 							continue;
 
 						Genode::Xml_node target = service_node.sub_node();

ports/run/noux_gdb.run

@@ -195,10 +195,10 @@ append config {
 			<resource name="RAM" quantum="1G"/>
 			<route>
 				<service name="Terminal">
-					<if-arg key="label" value="noux"/><child name="terminal_noux"/>
+					<if-arg key="label" value=""/><child name="terminal_noux"/>
 				</service>
 				<service name="Terminal">
-					<if-arg key="label" value="noux -> noux(terminal_fs)"/><child name="terminal_gdb"/>
+					<if-arg key="label" value="noux(terminal_fs)"/><child name="terminal_gdb"/>
 				</service>
 				<any-service><parent/><any-child/></any-service>
 			</route>

ports/run/noux_terminal_fs.run

@@ -163,10 +163,10 @@ append config {
 		<resource name="RAM" quantum="1G" />
 		<route>
 			<service name="Terminal">
-				<if-arg key="label" value="noux"/><child name="terminal_noux"/>
+				<if-arg key="label" value=""/><child name="terminal_noux"/>
 			</service>
 			<service name="Terminal">
-				<if-arg key="label" value="noux -> noux(terminal_fs)"/><child name="terminal_test"/>
+				<if-arg key="label" value="noux(terminal_fs)"/><child name="terminal_test"/>
 			</service>
 			<any-service><parent/><any-child/></any-service>
 		</route>