/*
 * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 *
 * You can also choose to distribute this program under the terms of
 * the Unmodified Binary Distribution Licence (as given in the file
 * COPYING.UBDL), provided that you have satisfied its requirements.
 */

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );

/** @file
 *
 * Linux entropy source
 *
 */

#include <stdint.h>
#include <errno.h>
#include <linux_api.h>
#include <ipxe/entropy.h>

/** Entropy source filename */
static const char entropy_filename[] = "/dev/random";

/** Entropy source file handle */
static int entropy_fd;

/**
 * Enable entropy gathering
 *
 * @ret rc		Return status code
 */
static int linux_entropy_enable ( void ) {

	/* Open entropy source */
	entropy_fd = linux_open ( entropy_filename, O_RDONLY );
	if ( entropy_fd < 0 ) {
		DBGC ( &entropy_fd, "ENTROPY could not open %s: %s\n",
		       entropy_filename, linux_strerror ( linux_errno ) );
		return entropy_fd;
	}

	return 0;
}

/**
 * Disable entropy gathering
 *
 */
static void linux_entropy_disable ( void ) {

	/* Close entropy source */
	linux_close ( entropy_fd );
}

/**
 * Get noise sample
 *
 * @ret noise		Noise sample
 * @ret rc		Return status code
 */
static int linux_get_noise ( noise_sample_t *noise ) {
	uint8_t byte;
	ssize_t len;

	/* Read a single byte from entropy source */
	len = linux_read ( entropy_fd, &byte, sizeof ( byte ) );
	if ( len < 0 ) {
		DBGC ( &entropy_fd, "ENTROPY could not read from %s: %s\n",
		       entropy_filename, linux_strerror ( linux_errno ) );
		return len;
	}
	if ( len == 0 ) {
		DBGC ( &entropy_fd, "ENTROPY EOF on reading from %s: %s\n",
		       entropy_filename, linux_strerror ( linux_errno ) );
		return -EPIPE;
	}
	*noise = byte;

	return 0;
}

PROVIDE_ENTROPY_INLINE ( linux, min_entropy_per_sample );
PROVIDE_ENTROPY ( linux, entropy_enable, linux_entropy_enable );
PROVIDE_ENTROPY ( linux, entropy_disable, linux_entropy_disable );
PROVIDE_ENTROPY ( linux, get_noise, linux_get_noise );