/*
 * \brief  Jitterentropy based random file system
 * \author Josef Soentgen
 * \date   2014-08-19
 */

/*
 * 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 _JITTERENTROPY_FILE_SYSTEM_H_
#define _JITTERENTROPY_FILE_SYSTEM_H_

/* Genode includes */
#include <util/xml_node.h>
#include <vfs/single_file_system.h>

/* jitterentropy includes */
extern "C" {
#include <jitterentropy.h>
}

class Jitterentropy_file_system : public Vfs::Single_file_system
{
	private:

		struct rand_data *_ec_stir;
		bool              _initialized;

		bool _init_jitterentropy()
		{
			int err = jent_entropy_init();
			if (err) {
				PERR("jitterentropy library could not be initialized!");
				return false;
			}

			/* use the default behaviour as specified in jitterentropy(3) */
			_ec_stir = jent_entropy_collector_alloc(0, 0);
			if (!_ec_stir) {
				PERR("jitterentropy could not allocate entropy collector!");
				return false;
			}

			return true;
		}

	public:

		Jitterentropy_file_system(Genode::Xml_node config)
		:
			Single_file_system(NODE_TYPE_CHAR_DEVICE, name(), config),
			_ec_stir(0),
			_initialized(_init_jitterentropy())
		{ }

		~Jitterentropy_file_system()
		{
			if (_initialized)
				jent_entropy_collector_free(_ec_stir);
		}

		static char const *name() { return "jitterentropy"; }


		/********************************
		 ** File I/O service interface **
		 ********************************/

		Write_result write(Vfs::Vfs_handle *, char const *,
		                   Vfs::file_size count,
		                   Vfs::file_size &count_out) override
		{
			return WRITE_ERR_IO;
		}

		Read_result read(Vfs::Vfs_handle *vfs_handle, char *dst,
		                 Vfs::file_size count,
		                 Vfs::file_size &out_count) override
		{
			if (!_initialized)
				return READ_ERR_IO;

			enum { MAX_BUF_LEN = 256 };
			char buf[MAX_BUF_LEN];

			size_t len = count > MAX_BUF_LEN ? MAX_BUF_LEN : count;

			if (jent_read_entropy(_ec_stir, buf, len) < 0)
				return READ_ERR_IO;

			Genode::memcpy(dst, buf, len);

			out_count = len;

			return READ_OK;
		}
};

#endif /* _JITTERENTROPY_FILE_SYSTEM_H_ */