[1651] Control interface in DHCPv4 refactored into separate class

- See ControlledDhcpv4Srv class for msgq support.

doc/devel/02-dhcp.dox

@@ -20,11 +20,20 @@
  * @section dhcpv4Session BIND10 message queue integration
  *
  * DHCPv4 server component is now integrated with BIND10 message queue.
- * The integration is performed by establish_session() and disconnect_session()
- * functions in src/bin/dhcp4/main.cc file. isc::cc::Session cc_session
+ * The integration is performed by establishSession() and disconnectSession()
+ * functions in isc::dhcp::ControlledDhcpv4Srv class. main() method deifined
+ * in the src/bin/dhcp4/main.cc file instantiates isc::dhcp::ControlledDhcpv4Srv
+ * class that establishes connection with msgq and install necessary handlers
+ * for receiving commands and configuration updates. It is derived from
+ * a base isc::dhcp::Dhcpv4Srv class that implements DHCPv4 server functionality,
+ * without any controlling mechanisms.
+ *
+ * ControlledDhcpv4Srv instantiates several components to make management
+ * session possible. In particular, isc::cc::Session cc_session
  * object uses ASIO for establishing connection. It registers its socket
- * in isc::asiolink::IOService io_service object. Typically, other components that
- * use ASIO for their communication, register their other sockets in the
+ * in isc::asiolink::IOService io_service object. Typically, other components
+ * (e.g. auth or resolver) that use ASIO for their communication, register their
+ * other sockets in the
  * same io_service and then just call io_service.run() method that does
  * not return, until one of the callback decides that it is time to shut down
  * the whole component cal calls io_service.stop(). DHCPv4 works in a
@@ -43,7 +52,10 @@
  * be used with and without message queue. Second benefit is related to the
  * first one: \ref libdhcp is supposed to be simple and robust and not require
  * many dependencies. One notable example of a use case that benefits from
- * this approach is a perfdhcp tool.
+ * this approach is a perfdhcp tool. Finally, the idea is that it should be
+ * possible to instantiate Dhcpv4Srv object directly, thus getting a server
+ * that does not support msgq. That is useful for embedded environments.
+ * It may also be useful in validation.
  *
  * @page dhcpv6 DHCPv6 Server Component
  *