Commit 5acb3cb5 authored by Tomek Mrugalski's avatar Tomek Mrugalski 🛰
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[3398] The result of configuration design discussion added

parent 777dbdb2
/**
* @page dhcpv4 DHCPv4 Server Component
*
* BIND10 offers DHCPv4 server implementation. It is implemented as
* b10-dhcp4 component. Its primary code is located in
* isc::dhcp::Dhcpv4Srv class. It uses \ref libdhcp extensively,
* especially isc::dhcp::Pkt4, isc::dhcp::Option and
* isc::dhcp::IfaceMgr classes. Currently this code offers skeleton
* functionality, i.e. it is able to receive and process incoming
* requests and trasmit responses. However, it does not have database
* management, so it returns only one, hardcoded lease to whoever asks
* for it.
*
* DHCPv4 server component does not support direct traffic (relayed
* only), as support for transmission to hosts without IPv4 address
* assigned is not implemented in IfaceMgr yet.
*
* DHCPv4 server component does not use BIND10 logging yet.
*
* @section dhcpv4Session BIND10 message queue integration
*
* DHCPv4 server component is now integrated with the BIND10 message queue.
* The integration is performed by establishSession() and disconnectSession()
* functions in isc::dhcp::ControlledDhcpv4Srv class. main() method defined
* 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
* (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
* different way. It does receive messages using select()
* (see isc::dhcp::IfaceMgr::receive4()), which is incompatible with ASIO.
* To solve this problem, socket descriptor is extracted from cc_session
* object and is passed to IfaceMgr by using isc::dhcp::IfaceMgr::set_session_socket().
* IfaceMgr then uses this socket in its select() call. If there is some
* data to be read, it calls registered callback that is supposed to
* read and process incoming data.
*
* This somewhat complicated approach is needed for a simple reason. In
* embedded deployments there will be no message queue. Not referring directly
* to anything related to message queue in isc::dhcp::Dhcpv4Srv and
* isc::dhcp::IfaceMgr classes brings in two benefits. First, the can
* 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. 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.
*
*/
......@@ -86,6 +86,10 @@
* - @subpage cfgmgr
* - @subpage allocengine
* - @subpage dhcpDatabaseBackends
* - @subpage configBackend
* - @subpage configBackendMotivation
* - @subpage configBackendJSONDesign
* - @subpage configBackendAdding
* - @subpage perfdhcpInternals
* - @subpage libdhcp_ddns
*
......@@ -94,6 +98,7 @@
* - @subpage logBasicIdeas
* - @subpage logDeveloperUse
* - @subpage logNotes
* - @subpage LoggingApi
* - @subpage SocketSessionUtility
* - <a href="./doxygen-error.log">Documentation warnings and errors</a>
*
......
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