Add API to query hardware port name

In case of internal backends this allows to retrieve the
Device name for a given (hashed unique) port-name.

As opposed to "pretty-name" (which defaults to hw-port-name),
this cannot be changed by the user.

It is intended to be used when probing for control surfaces.

libs/ardour/ardour/port_manager.h

@@ -160,6 +160,7 @@ public:
 	std::string             make_port_name_relative (const std::string& name) const;
 	std::string             make_port_name_non_relative (const std::string& name) const;
 	std::string             get_pretty_name_by_name (const std::string& portname) const;
+	std::string             get_hardware_port_name_by_name (const std::string& portname) const;
 	std::string             short_port_name_from_port_name (std::string const& full_name) const;
 	bool                    port_is_mine (const std::string& fullname) const;
 

libs/ardour/port_engine_shared.cc

@@ -616,6 +616,12 @@ PortEngineSharedImpl::get_port_property (PortEngine::PortHandle port, const std:
 			return 0;
 		}
 	}
+	if (key == "http://ardour.org/metadata/hardware-port-name") {
+		value = std::static_pointer_cast<BackendPort>(port)->hw_port_name ();
+		if (!value.empty()) {
+			return 0;
+		}
+	}
 	return -1;
 }
 

libs/ardour/port_manager.cc

@@ -355,6 +355,26 @@ PortManager::get_pretty_name_by_name (const std::string& portname) const
 	return string ();
 }
 
+std::string
+PortManager::get_hardware_port_name_by_name (const std::string& portname) const
+{
+	PortEngine::PortHandle ph = _backend->get_port_by_name (portname);
+
+	if (ph) {
+		std::string value;
+		std::string type;
+		if (0 == _backend->get_port_property (ph, "http://ardour.org/metadata/hardware-port-name", value, type)) {
+			return value;
+		} else {
+			return short_port_name_from_port_name (portname);
+		}
+	}
+
+	return string ();
+}
+
+
+
 bool
 PortManager::port_is_mine (const string& portname) const
 {