genode/repos/os/include/init/child_config.h

/*
 * \brief  Utility for handling child configuration
 * \author Norman Feske
 * \date   2008-03-22
 */

/*
 * Copyright (C) 2008-2013 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 _INCLUDE__INIT__CHILD_CONFIG_H_
#define _INCLUDE__INIT__CHILD_CONFIG_H_

#include <base/env.h>
#include <base/printf.h>
#include <util/xml_node.h>
#include <rom_session/connection.h>
#include <ram_session/client.h>

namespace Init { class Child_config; }


class Init::Child_config
{
	private:

		enum { CONFIGFILE_NAME_LEN = 64 };
		char _filename[CONFIGFILE_NAME_LEN];

		Genode::Ram_session_capability   _ram_session_cap;
		Genode::Ram_dataspace_capability _config_ram_ds;

	public:

		/**
		 * Constructor
		 *
		 * The provided RAM session is used to obtain a dataspace for
		 * holding the copy of the child's configuration data unless the
		 * configuration is supplied via a config file. Normally, the
		 * child's RAM session should be used to account the consumed RAM
		 * quota to the child.
		 */
		Child_config(Genode::Ram_session_capability ram_session,
		             Genode::Xml_node               start_node)
		: _ram_session_cap(ram_session)
		{
			using namespace Genode;

			/*
			 * If the start node contains a 'filename' entry, we only keep
			 * the information about the file name.
			 */
			_filename[0] = 0;
			try {
				Xml_node configfile_node = start_node.sub_node("configfile");
				configfile_node.attribute("name")
					.value(_filename, sizeof(_filename));

				return;
			} catch (...) { }

			/*
			 * If the start node contains a 'config' entry, we copy this
			 * entry into a fresh dataspace to be provided to our child.
			 */
			Ram_session_client rsc(_ram_session_cap);
			try {
				Xml_node config_node = start_node.sub_node("config");

				const char *config = config_node.addr();
				Genode::size_t config_size = config_node.size();

				if (!config || !config_size) return;

				/*
				 * Allocate RAM dataspace that is big enough to
				 * hold the configuration and the null termination.
				 */
				_config_ram_ds = rsc.alloc(config_size + 1);

				/*
				 * Make dataspace locally accessible, copy
				 * configuration into the dataspace, and append
				 * a string-terminating zero.
				 */
				void *addr = env()->rm_session()->attach(_config_ram_ds);

				Genode::memcpy(addr, config, config_size);
				static_cast<char *>(addr)[config_size] = 0;
				env()->rm_session()->detach(addr);

			} catch (Region_map::Attach_failed) {
				rsc.free(_config_ram_ds);
				return;
			} catch (Ram_session::Alloc_failed) {
				return;
			} catch (Xml_node::Nonexistent_sub_node) { }
		}

		/**
		 * Destructor
		 */
		~Child_config()
		{
			using namespace Genode;

			/*
			 * The configuration data is either provided as a ROM session
			 * (holding a complete configfile) or as a RAM dataspace
			 * holding a copy of the start node's config entry. In the
			 * latter case, the child's configuration resides in a
			 * shadow copy kept in '_config_ram_ds'.
			 */
			if (_config_ram_ds.valid())
				Ram_session_client(_ram_session_cap).free(_config_ram_ds);
		}

		/**
		 * Return file name if configuration comes from a file
		 *
		 * If the configuration is provided inline, the method returns 0.
		 */
		char const *filename() const {
			return _filename[0] != 0 ? _filename : 0; }

		/**
		 * Request dataspace holding the start node's configuration data
		 *
		 * This method returns a valid dataspace only when using an
		 * inline configuration (if 'filename()' returns 0).
		 */
		Genode::Dataspace_capability dataspace() {
			return Genode::Dataspace_capability(_config_ram_ds); }
};

#endif /* _INCLUDE__INIT__CHILD_CONFIG_H_ */