genode/repos/os/src/server/report_rom/rom_registry.h

/*
 * \brief  Registry of ROM modules
 * \author Norman Feske
 * \date   2014-01-11
 */

/*
 * Copyright (C) 2014 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU General Public License version 2.
 */

#ifndef _ROM_REGISTRY_H_
#define _ROM_REGISTRY_H_

/* Genode includes */
#include <report_rom/rom_registry.h>
#include <os/session_policy.h>

namespace Rom { struct Registry; }


struct Rom::Registry : Registry_for_reader, Registry_for_writer, Genode::Noncopyable
{
	private:

		Genode::Allocator &_md_alloc;

		Module_list _modules;

		struct Read_write_policy : Module::Read_policy, Module::Write_policy
		{
			bool read_permitted(Module const &,
			                    Writer const &,
			                    Reader const &) const override
			{
				/*
				 * The access-control policy is applied at the ROM-session
				 * construction time by applying the '_report_name' method
				 * on the session label. Once connected to a ROM module,
				 * the ROM client is always allowed to read the ROM content.
				 */
				return true;
			}

			bool write_permitted(Module const &, Writer const &) const override
			{
				/*
				 * Because the report-session label is used as the module name
				 * for the writer, each report session refers to a distinct
				 * module. Report client can write to their respective modules
				 * at any time.
				 */
				return true;
			}

		} _read_write_policy;

		Module &_lookup(Module::Name const name)
		{
			for (Module *m = _modules.first(); m; m = m->next())
				if (m->_has_name(name))
					return *m;

			/* module does not exist yet, create one */

			/* XXX proper accounting for the used memory is missing */
			/* XXX if we run out of memory, the server will abort */

			Module * const module = new (&_md_alloc)
				Module(name, _read_write_policy, _read_write_policy);

			_modules.insert(module);
			return *module;
		}

		void _try_to_destroy(Module const &module)
		{
			if (module._is_in_use())
				return;

			_modules.remove(&module);
			Genode::destroy(&_md_alloc, const_cast<Module *>(&module));
		}

		template <typename USER>
		Module &_lookup(USER &user, Module::Name const &name)
		{
			Module &module = _lookup(name);
			module._register(user);
			return module;
		}

		template <typename USER>
		void _release(USER &user, Module const &module)
		{
			/*
			 * The '_release' function is called by both the report service
			 * and the ROM service. The latter has merely a 'const' version
			 * of the module because it is not supposed to modify it. However,
			 * when closing a ROM session, we have to disassociate the ROM
			 * session from the module. To do that, we need a non-const
			 * reference to the module.
			 */
			const_cast<Module &>(module)._unregister(user);
			_try_to_destroy(module);
		}

		/**
		 * Return report name that corresponds to the given ROM session label
		 *
		 * \throw Registry_for_reader::Lookup_failed
		 */
		Module::Name _report_name(Module::Name const &rom_label) const
		{
			using namespace Genode;

			String<Rom::Module::Name::capacity()> report;

			try {
				Session_policy policy(rom_label);
				policy.attribute("report").value(&report);
				return Rom::Module::Name(report.string());
			} catch (Session_policy::No_policy_defined) {
				/* FIXME backwards compatibility, remove at next release */
				try {
					Xml_node rom_node = config()->xml_node().sub_node("rom");
					PWRN("parsing legacy <rom> policies");

					Session_policy policy(rom_label, rom_node);
					policy.attribute("report").value(&report);
					return Rom::Module::Name(report.string());
				} catch (Xml_node::Nonexistent_sub_node)    { /* no <rom> node */ }
				  catch (Session_policy::No_policy_defined) { }
			}

			PWRN("no valid policy for label \"%s\"", rom_label.string());
			throw Root::Invalid_args();
		}

	public:

		Registry(Genode::Allocator &md_alloc)
		:
			_md_alloc(md_alloc)
		{ }

		Module &lookup(Writer &writer, Module::Name const &name) override
		{
			Module &module = _lookup(writer, name);

			/*
			 * Enforce invariant that each module can have only one writer at a
			 * time.
			 */
			if (module._num_writers() > 1) {
				release(writer, module);
				throw Root::Invalid_args();
			}

			return module;
		}

		void release(Writer &writer, Module &module) override
		{
			return _release(writer, module);
		}

		Readable_module &lookup(Reader &reader, Module::Name const &rom_label) override
		{
			return _lookup(reader, _report_name(rom_label));
		}

		void release(Reader &reader, Readable_module &module) override
		{
			return _release(reader, static_cast<Module &>(module));
		}
};

#endif /* _ROM_REGISTRY_H_ */