genode/repos/base/include/base/rpc_server.h

/*
 * \brief  Server-side API of the RPC framework
 * \author Norman Feske
 * \date   2006-04-28
 */

/*
 * Copyright (C) 2006-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

#ifndef _INCLUDE__BASE__RPC_SERVER_H_
#define _INCLUDE__BASE__RPC_SERVER_H_

#include <base/rpc.h>
#include <base/thread.h>
#include <base/ipc.h>
#include <base/object_pool.h>
#include <base/lock.h>
#include <base/log.h>
#include <base/trace/events.h>
#include <pd_session/pd_session.h>

namespace Genode {

	class Ipc_server;

	template <typename, typename> class Rpc_dispatcher;
	class Rpc_object_base;
	template <typename, typename> struct Rpc_object;
	class Rpc_entrypoint;

	class Signal_receiver;
}


/**
 * RPC dispatcher implementing the specified RPC interface
 *
 * \param RPC_INTERFACE  class providing the RPC interface description
 * \param SERVER         class to invoke for the server-side RPC functions
 *
 * This class is the base class of each server-side RPC implementation. It
 * contains the logic for dispatching incoming RPC requests and calls the
 * server functions according to the RPC declarations in 'RPC_INTERFACE'.
 *
 * If using the default argument for 'SERVER', the 'RPC_INTERFACE' is expected
 * to contain the abstract interface for all RPC functions. So virtual methods
 * must be declared in 'RPC_INTERFACE'. In contrast, by explicitly specifying
 * the 'SERVER' argument, the server-side dispatching performs direct
 * calls to the respective methods of the 'SERVER' class and thereby
 * omits virtual method calls.
 */
template <typename RPC_INTERFACE, typename SERVER = RPC_INTERFACE>
class Genode::Rpc_dispatcher : public RPC_INTERFACE
{
	/**
	 * Shortcut for the type list of RPC functions provided by this server
	 * component
	 */
	typedef typename RPC_INTERFACE::Rpc_functions Rpc_functions;

	protected:

		template <typename ARG_LIST>
		ARG_LIST _read_args(Ipc_unmarshaller &msg,
		                    Meta::Overload_selector<ARG_LIST>)
		{
			typename Trait::Rpc_direction<typename ARG_LIST::Head>::Type direction;
			typedef typename ARG_LIST::Stored_head Arg;
			Arg arg = _read_arg<Arg>(msg, direction);

			Meta::Overload_selector<typename ARG_LIST::Tail> tail_selector;
			typename ARG_LIST::Tail subsequent_args = _read_args(msg,
			                                                     tail_selector);

			ARG_LIST args { arg, subsequent_args };
			return args;
		}

		Meta::Empty _read_args(Ipc_unmarshaller &,
		                       Meta::Overload_selector<Meta::Empty>)
		{
			return Meta::Empty();
		}

		template <typename ARG>
		ARG _read_arg(Ipc_unmarshaller &msg, Rpc_arg_in)
		{
			return msg.extract(Meta::Overload_selector<ARG>());
		}

		template <typename ARG>
		ARG _read_arg(Ipc_unmarshaller &msg, Rpc_arg_inout)
		{
			return _read_arg<ARG>(msg, Rpc_arg_in());
		}

		template <typename ARG>
		ARG _read_arg(Ipc_unmarshaller &msg, Rpc_arg_out)
		{
			return ARG();
		}

		template <typename ARG_LIST>
		void _write_results(Msgbuf_base &msg, ARG_LIST &args)
		{
			if (Trait::Rpc_direction<typename ARG_LIST::Head>::Type::OUT)
				msg.insert(args._1);

			_write_results(msg, args._2);
		}

		void _write_results(Msgbuf_base &, Meta::Empty) { }

		template <typename RPC_FUNCTION, typename EXC_TL>
		typename RPC_FUNCTION::Ret_type
		_do_serve(typename RPC_FUNCTION::Server_args &args,
		           Meta::Overload_selector<RPC_FUNCTION, EXC_TL>)
		{
			enum { EXCEPTION_CODE = Rpc_exception_code::EXCEPTION_BASE
			                      - Meta::Length<EXC_TL>::Value };
			try {
				typedef typename EXC_TL::Tail Exc_tail;
				return _do_serve(args,
				                 Meta::Overload_selector<RPC_FUNCTION, Exc_tail>());
			} catch (typename EXC_TL::Head) {
				/**
				 * By passing the exception code through an exception we ensure that
				 * a return value is only returned if it exists. This way, the return
				 * type does not have to be default-constructible.
				 */
				throw Rpc_exception_code(EXCEPTION_CODE);
			}
		}

		template <typename RPC_FUNCTION>
		typename RPC_FUNCTION::Ret_type
		_do_serve(typename RPC_FUNCTION::Server_args &args,
		          Meta::Overload_selector<RPC_FUNCTION, Meta::Empty>)
		{
			typedef typename RPC_FUNCTION::Ret_type Ret_type;
			SERVER *me = static_cast<SERVER *>(this);
			return RPC_FUNCTION::template serve<SERVER, Ret_type>(*me, args);
		}

		template <typename RPC_FUNCTIONS_TO_CHECK>
		Rpc_exception_code _do_dispatch(Rpc_opcode opcode,
		                                Ipc_unmarshaller &in, Msgbuf_base &out,
		                                Meta::Overload_selector<RPC_FUNCTIONS_TO_CHECK>)
		{
			using namespace Meta;

			typedef typename RPC_FUNCTIONS_TO_CHECK::Head This_rpc_function;

			if (opcode.value == Index_of<Rpc_functions, This_rpc_function>::Value) {

				/* read arguments from incoming message */
				typedef typename This_rpc_function::Server_args Server_args;
				Meta::Overload_selector<Server_args> arg_selector;
				Server_args args = _read_args(in, arg_selector);

				{
					Trace::Rpc_dispatch trace_event(This_rpc_function::name());
				}

				/*
				 * Dispatch call to matching RPC base class, using
				 * 'This_rpc_function' and the list of its exceptions to
				 * select the overload.
				 */

				typedef typename This_rpc_function::Ret_type Ret_type;
				Rpc_exception_code exc(Rpc_exception_code::SUCCESS);
				try {
					typedef typename This_rpc_function::Exceptions Exceptions;
					Overload_selector<This_rpc_function, Exceptions> overloader;
					Ret_type ret = _do_serve(args, overloader);

					_write_results(out, args);
					out.insert(ret);
				} catch (Rpc_exception_code thrown) {
					/**
					 * Output arguments may be modified although an exception was thrown.
					 * However, a return value does not exist. So we do not insert one.
					 */
					_write_results(out, args);
					exc = thrown;
				}

				{
					Trace::Rpc_reply trace_event(This_rpc_function::name());
				}

				return exc;
			}

			typedef typename RPC_FUNCTIONS_TO_CHECK::Tail Tail;
			return _do_dispatch(opcode, in, out, Overload_selector<Tail>());
		}

		Rpc_exception_code _do_dispatch(Rpc_opcode opcode,
		                                Ipc_unmarshaller &, Msgbuf_base &,
		                                Meta::Overload_selector<Meta::Empty>)
		{
			error("invalid opcode ", opcode.value);
			return Rpc_exception_code(Rpc_exception_code::INVALID_OPCODE);
		}

		/**
		 * Handle corner case of having an RPC interface with no RPC functions
		 */
		Rpc_exception_code _do_dispatch(Rpc_opcode,
		                                Ipc_unmarshaller &, Msgbuf_base &,
		                                Meta::Overload_selector<Meta::Type_list<> >)
		{
			return Rpc_exception_code(Rpc_exception_code::SUCCESS);
		}

		/**
		 * Protected constructor
		 *
		 * This class is only usable as base class.
		 */
		Rpc_dispatcher() { }

	public:

		Rpc_exception_code dispatch(Rpc_opcode opcode,
		                            Ipc_unmarshaller &in, Msgbuf_base &out)
		{
			return _do_dispatch(opcode, in, out,
			                    Meta::Overload_selector<Rpc_functions>());
		}
};


class Genode::Rpc_object_base : public Object_pool<Rpc_object_base>::Entry
{
	public:

		virtual ~Rpc_object_base() { }

		/**
		 * Interface to be implemented by a derived class
		 *
		 * \param op   opcode of invoked method
		 * \param in   incoming message with method arguments
		 * \param out  outgoing message for storing method results
		 */
		virtual Rpc_exception_code
		dispatch(Rpc_opcode op, Ipc_unmarshaller &in, Msgbuf_base &out) = 0;
};


/**
 * Object that is accessible from remote protection domains
 *
 * A 'Rpc_object' is a locally implemented object that can be referenced
 * from the outer world using a capability. The capability gets created
 * when attaching a 'Rpc_object' to a 'Rpc_entrypoint'.
 */
template <typename RPC_INTERFACE, typename SERVER = RPC_INTERFACE>
struct Genode::Rpc_object : Rpc_object_base, Rpc_dispatcher<RPC_INTERFACE, SERVER>
{
	struct Capability_guard;

	Rpc_exception_code dispatch(Rpc_opcode opcode, Ipc_unmarshaller &in, Msgbuf_base &out) override
	{
		return Rpc_dispatcher<RPC_INTERFACE, SERVER>::dispatch(opcode, in, out);
	}

	Capability<RPC_INTERFACE> const cap() const
	{
		return reinterpret_cap_cast<RPC_INTERFACE>(Rpc_object_base::cap());
	}
};


/**
 * RPC entrypoint serving RPC objects
 *
 * The entrypoint's thread will initialize its capability but will not
 * immediately enable the processing of requests. This way, the
 * activation-using server can ensure that it gets initialized completely
 * before the first capability invocations come in. Once the server is
 * ready, it must enable the entrypoint explicitly by calling the
 * 'activate()' method. The 'start_on_construction' argument is a
 * shortcut for the common case where the server's capability is handed
 * over to other parties _after_ the server is completely initialized.
 */
class Genode::Rpc_entrypoint : Thread, public Object_pool<Rpc_object_base>
{
	/**
	 * This is only needed because in 'base-hw' we need the Thread
	 * pointer of the entrypoint to cancel its next signal blocking.
	 * Remove it as soon as signal dispatching in 'base-hw' doesn't need
	 * multiple threads anymore.
	 */
	friend class Signal_receiver;

	private:

		/**
		 * Prototype capability to derive capabilities for RPC objects
		 * from.
		 */
		Untyped_capability _cap { };

		enum { SND_BUF_SIZE = 1024, RCV_BUF_SIZE = 1024 };
		Msgbuf<SND_BUF_SIZE> _snd_buf { };
		Msgbuf<RCV_BUF_SIZE> _rcv_buf { };

		/**
		 * Hook to let low-level thread init code access private members
		 *
		 * This method is only used on NOVA.
		 */
		static void _activation_entry();

		struct Exit : Genode::Interface
		{
			GENODE_RPC(Rpc_exit, void, _exit);
			GENODE_RPC_INTERFACE(Rpc_exit);
		};

		struct Exit_handler : Rpc_object<Exit, Exit_handler>
		{
			int exit;

			Exit_handler() : exit(false) { }

			void _exit() { exit = true; }
		};

	protected:

		Native_capability _caller       { };
		Lock              _cap_valid    { };  /* thread startup synchronization        */
		Lock              _delay_start  { };  /* delay start of request dispatching    */
		Lock              _delay_exit   { };  /* delay destructor until server settled */
		Pd_session       &_pd_session;        /* for creating capabilities             */
		Exit_handler      _exit_handler { };
		Capability<Exit>  _exit_cap     { };

		/**
		 * Access to kernel-specific part of the PD session interface
		 *
		 * Some kernels like NOVA need a special interface for creating RPC
		 * object capabilities.
		 */
		Capability<Pd_session::Native_pd> _native_pd_cap { };

		/**
		 * Back end used to associate RPC object with the entry point
		 *
		 * \noapi
		 */
		Untyped_capability _manage(Rpc_object_base *obj);

		/**
		 * Back end used to Dissolve RPC object from entry point
		 *
		 * \noapi
		 */
		void _dissolve(Rpc_object_base *obj);

		/**
		 * Wait until the entrypoint activation is initialized
		 *
		 * \noapi
		 */
		void _block_until_cap_valid();

		/**
		 * Allocate new RPC object capability
		 *
		 * Regular servers allocate capabilities from their protection domain
		 * via the component's environment. This method allows core to have a
		 * special implementation that does not rely on a PD session.
		 *
		 * The 'entry' argument is used only on NOVA. It is the server-side
		 * instruction pointer to be associated with the RPC object capability.
		 */
		Native_capability _alloc_rpc_cap(Pd_session &, Native_capability ep,
		                                 addr_t entry = 0);

		/**
		 * Free RPC object capability
		 */
		void _free_rpc_cap(Pd_session &, Native_capability);

		/**
		 * Thread interface
		 *
		 * \noapi
		 */
		void entry() override;

	public:

		/**
		 * Constructor
		 *
		 * \param pd_session   'Pd_session' for creating capabilities
		 *                     for the RPC objects managed by this entry
		 *                     point
		 * \param stack_size   stack size of entrypoint thread
		 * \param name         name of entrypoint thread
		 * \param location     CPU affinity
		 */
		Rpc_entrypoint(Pd_session *pd_session, size_t stack_size,
		               char const *name, bool start_on_construction = true,
		               Affinity::Location location = Affinity::Location());

		~Rpc_entrypoint();

		/**
		 * Associate RPC object with the entry point
		 */
		template <typename RPC_INTERFACE, typename RPC_SERVER>
		Capability<RPC_INTERFACE>
		manage(Rpc_object<RPC_INTERFACE, RPC_SERVER> *obj)
		{
			return reinterpret_cap_cast<RPC_INTERFACE>(_manage(obj));
		}

		/**
		 * Dissolve RPC object from entry point
		 */
		template <typename RPC_INTERFACE, typename RPC_SERVER>
		void dissolve(Rpc_object<RPC_INTERFACE, RPC_SERVER> *obj)
		{
			_dissolve(obj);
		}

		/**
		 * Activate entrypoint, start processing RPC requests
		 */
		void activate();

		/**
		 * Request reply capability for current call
		 *
		 * \noapi
		 *
		 * Note: This is a temporary API method, which is going to be
		 * removed. Please do not use this method.
		 *
		 * Typically, a capability obtained via this method is used as
		 * argument of 'intermediate_reply'.
		 */
		Untyped_capability reply_dst() { return _caller; }

		/**
		 * Prevent reply of current request
		 *
		 * \noapi
		 *
		 * Note: This is a temporary API method, which is going to be
		 * removed. Please do not use this method.
		 *
		 * This method can be used to keep the calling client blocked
		 * after the server has finished the processing of the client's
		 * request. At a later time, the server may chose to unblock the
		 * client via the 'intermedate_reply' method.
		 */
		void omit_reply() { _caller = Native_capability(); }

		/**
		 * Send a reply out of the normal call-reply order
		 *
		 * \noapi
		 *
		 * In combination with the 'reply_dst' accessor method, this method
		 * allows for the dispatching of client requests out of order. The only
		 * designated user of this method is core's PD service. The
		 * 'Pd_session::submit' RPC function uses it to send a reply to a
		 * caller of the 'Signal_source::wait_for_signal' RPC function before
		 * returning from the 'submit' call.
		 */
		void reply_signal_info(Untyped_capability reply_cap,
		                       unsigned long imprint, unsigned long cnt);

		/**
		 * Return true if the caller corresponds to the entrypoint called
		 *
		 * \noapi
		 *
		 * This method is solely needed on Linux.
		 */
		bool is_myself() const;

		/**
		 * Required outside of core. E.g. launchpad needs it to forcefully kill
		 * a client which blocks on a session opening request where the service
		 * is not up yet.
		 */
		void cancel_blocking() { Thread::cancel_blocking(); }
};


template <typename IF, typename SERVER>
struct Genode::Rpc_object<IF, SERVER>::Capability_guard
{
	Rpc_entrypoint &_ep;
	Rpc_object     &_obj;

	Capability_guard(Rpc_entrypoint &ep, Rpc_object &obj)
	: _ep(ep), _obj(obj) { _ep.manage(&_obj); }

	~Capability_guard() { _ep.dissolve(&_obj); }
};

#endif /* _INCLUDE__BASE__RPC_SERVER_H_ */