nic_router: rework round-trip-time handling

Do not use two times the RTT for the lifetime of links but use it as
it is configured to simplify the usage of the router. Internally, use
Microseconds/Duration type instead of plain integers.

Ref #2490

repos/libports/run/nic_dump.run

@@ -178,7 +178,7 @@ append config {
 	<start name="nic_router" caps="200">
 		<resource name="RAM" quantum="10M"/>
 		<provides><service name="Nic"/></provides>
-		<config rtt_sec="3" verbose="no">
+		<config rtt_sec="6" verbose="no">
 
 			<policy label_prefix="udp_client_1"  domain="udp_client_1"  />
 			<policy label_prefix="http_client_3" domain="http_client_3" />

repos/libports/run/nic_router.run

@@ -197,7 +197,7 @@ append config {
 	<start name="nic_router" caps="200" priority="-1">
 		<resource name="RAM" quantum="10M"/>
 		<provides><service name="Nic"/></provides>
-		<config rtt_sec="3" verbose="no">
+		<config rtt_sec="6" verbose="no">
 
 			<policy label_prefix="udp_client_1"  domain="udp_client_1"  />
 			<policy label_prefix="http_client_3" domain="http_client_3" />

repos/os/src/server/nic_router/README

@@ -220,18 +220,18 @@ link states so you should choose it with care. If it is too low, replies that
 normally need no routing rule may get lost. If it is too high, link states are
 held longer than necessary.
 
-In general, each link state is discarded after a duration of two times the
-round-trip time without a matching packet. For UDP link states, this is the
-only rule and better known as hole punching. It allows peers to keep alive a
-UDP pseudo-connection through the router by frequently sending empty packets.
-The need for such a pseudo-connection arises from the router's demand to
-support NAT for UDP transfers and the consequence of keeping the corresponding
-mapping information.
+In general, each link state is discarded after a duration of the round-trip
+time without a matching packet. For UDP link states, this is the only rule and
+better known as hole punching. It allows peers to keep alive a UDP
+pseudo-connection through the router by frequently sending empty packets.  The
+need for such a pseudo-connection arises from the router's demand to support
+NAT for UDP transfers and the consequence of keeping the corresponding mapping
+information.
 
 The lifetime management of TCP link states, in contrast, is more complex. In
 addition to the common timeout, they may be discarded even if they still
 receive packets. This is the case when the router observed the four-way
-termination handshake of TCP and two times the round-trip time has passed.
+termination handshake of TCP and the round-trip time has passed.
 
 
 Configuring NAT

repos/os/src/server/nic_router/configuration.cc

@@ -23,29 +23,23 @@ using namespace Net;
 using namespace Genode;
 
 
-/***************
- ** Utilities **
- ***************/
-
-static unsigned read_rtt_sec(Xml_node const node)
+Microseconds Configuration::_init_rtt(Xml_node const node)
 {
-	unsigned const rtt_sec = node.attribute_value("rtt_sec", 0UL);
+	unsigned rtt_sec = node.attribute_value("rtt_sec", 0UL);
 	if (!rtt_sec) {
-		warning("fall back to default rtt_sec=\"3\"");
-		return 3;
+		warning("fall back to default rtt_sec=\"",
+		        (unsigned)DEFAULT_RTT_SEC, "\"");
+		rtt_sec = DEFAULT_RTT_SEC;
 	}
-	return rtt_sec;
+	return Microseconds(rtt_sec * 1000 * 1000);
 }
 
 
-/*******************
- ** Configuration **
- *******************/
-
-Configuration::Configuration(Xml_node const node, Allocator &alloc)
+Configuration::Configuration(Xml_node const  node,
+                             Allocator      &alloc)
 :
 	_alloc(alloc), _verbose(node.attribute_value("verbose", false)),
-	_rtt_sec(read_rtt_sec(node)), _node(node)
+	_rtt(_init_rtt(node)), _node(node)
 {
 	/* read domains */
 	node.for_each_sub_node("domain", [&] (Xml_node const node) {

repos/os/src/server/nic_router/configuration.h

@@ -17,6 +17,9 @@
 /* local includes */
 #include <domain.h>
 
+/* Genode includes */
+#include <os/duration.h>
+
 namespace Genode { class Allocator; }
 
 namespace Net { class Configuration; }
@@ -26,14 +29,18 @@ class Net::Configuration
 {
 	private:
 
-		Genode::Allocator      &_alloc;
-		bool             const  _verbose;
-		unsigned         const  _rtt_sec;
-		Domain_tree             _domains;
-		Genode::Xml_node const  _node;
+		Genode::Allocator          &_alloc;
+		bool                 const  _verbose;
+		Genode::Microseconds const  _rtt;
+		Domain_tree                 _domains;
+		Genode::Xml_node     const  _node;
+
+		Genode::Microseconds _init_rtt(Genode::Xml_node const node);
 
 	public:
 
+		enum { DEFAULT_RTT_SEC = 6 };
+
 		Configuration(Genode::Xml_node const node, Genode::Allocator &alloc);
 
 
@@ -41,10 +48,10 @@ class Net::Configuration
 		 ** Accessors **
 		 ***************/
 
-		bool              verbose() const { return _verbose; }
-		unsigned          rtt_sec() const { return _rtt_sec; }
-		Domain_tree      &domains()       { return _domains; }
-		Genode::Xml_node  node()    const { return _node; }
+		bool                  verbose() const { return _verbose; }
+		Genode::Microseconds  rtt()     const { return _rtt; }
+		Domain_tree          &domains()       { return _domains; }
+		Genode::Xml_node      node()    const { return _node; }
 };
 
 #endif /* _CONFIGURATION_H_ */

repos/os/src/server/nic_router/link.cc

@@ -124,7 +124,7 @@ Link::Link(Interface                           &cln_interface,
 	_server_port_alloc(srv_port_alloc),
 	_server(srv_interface, srv_id, *this),
 	_close_timeout(timer, *this, &Link::_handle_close_timeout),
-	_close_timeout_us(_config.rtt_sec() * 2 * 1000 * 1000),
+	_close_timeout_us(_config.rtt()),
 	_protocol(protocol)
 {
 	_close_timeout.schedule(_close_timeout_us);

repos/os/src/server/nic_router/link.h

@@ -124,8 +124,6 @@ class Net::Link : public Link_list::Element
 {
 	protected:
 
-		using Signal_handler = Genode::Signal_handler<Link>;
-
 		Configuration                       &_config;
 		Link_side                            _client;
 		Pointer<Port_allocator_guard> const  _server_port_alloc;