/*-
 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
 *
 * Copyright (c) 2005-2008 Poul-Henning Kamp
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * $FreeBSD$
 */

#ifndef __LOCAL_FIFOLOG_H_
#define __LOCAL_FIFOLOG_H_

/*
 * Definitions for fifolog "protocol": the on-media layout.
 *
 * The fifolog on-media record has three layers:
 *   The outer timestamping and synchronization layer.
 *   The zlib implemented data compression.
 *   The inner sequencing and identification layer.
 *
 * All three layers are synchronized at a subset of the outer layer
 * record boundaries, from where reading can be initiated.
 *
 *
 * The outer layer:
 * -----------------
 * The first record in a fifolog contains a magic string and version
 * information along with a 32be encoded recordsize for all records
 * in the fifolog, including the first.
 * The recordsize is explicit to avoid ambiguities when a media is
 * moved from one machine to another.
 *
 * Each record in the fifolog has the following contents:
 *	offset	type	contents
 *      --------------------------------------------------------------
 *	0	32be	sequence_number
 *			The sequence number is randomly chosen for the
 *			fifolog and increments once for each record written.
 *			It's presence allow quick identification of the next
 *			record to be written using a binary search for the
 *			first place where a discontinuity in the sequence
 *			numbers occur.
 *	4	 8	flags (FIFOLOG_FLG_*)
 *
 * If (flags & (FIFOLOG_FLG_SYNC)) the record is a synchronization point
 * at which the inner layers are aligned so that reading can be started
 * at this point.
 * To enable seeks into the file based on timestamps, a third field is
 * present in these records as well:
 *	5	32be	time_t containing POSIX's understanding of UTC.
 *
 * These fields are immediately followed by the inner layer payload as
 * described below, which has variable length.
 *
 * If the inner layer payload is shorter than the available space in
 * the record, it is padded with zero bytes, and the number of unused
 * bytes, including the encoded length thereof is recorded at the end
 * of the record as follows:
 *
 * If (flags & FIFOLOG_FLG_1BYTE)
 *	n-1	8	number of unused bytes
 * else if (flags & FIFOLOG_FLG_4BYTE)
 *	n-4	32be	number of unused bytes
 *
 *
 * The gzip layer
 * --------------
 * Is just output from zlib, nothing special here.  FIFOLOG_FLG_SYNC
 * corresponds to Z_FINISH flags to zlib.
 * In most cases, the timer will expire before zlib has filled an entire
 * record in which case Z_SYNC_FLUSH will be used to force as much as
 * possible into the buffer before it is written.  This is not marked
 * in outer layer (apart from a natural correlation with padding) since
 * zlibs data stream handles this without help.
 *
 *
 * The inner layer:
 * ----------------
 * The inner layer contains data identification and to the second
 * timestamping (the timestamp in the outer layer only marks the
 * first possible timestamp for content in the SYNC record).
 *
 *	offset	type	contents
 *      --------------------------------------------------------------
 *	0	32be	ident
 *
 * The bottom 30 bits of the identification word are application defined,
 * presently unused in the stand-alone fifolog tools, but used in the
 * original "measured" application that originated the fifolog format.
 * Should for instance syslogd(8) grow native support for fifolog format,
 * it could store the message priority here.
 *
 * If (ident & FIFOLOG_TIMESTAMP) the record is prefixed by:
 *	4	32be	time_t containing POSIX's understanding of UTC.
 *
 * Then follows the content, either as a NUL terminated string or as
 * a length encoded binary sequence:
 *
 * If (ident & FIFOLOG_LENGTH) the record is prefixed by:
 *	{0|4}	8	length of binary data
 *
 */

/* Magic identification string */
#define FIFOLOG_FMT_MAGIC	"Measured FIFOLOG Ver 1.01\n"

/* Offset of the 32be encoded recordsize in the first sector */
#define FIFOLOG_OFF_BS		0x20

#define FIFOLOG_FLG_1BYTE	0x01
#define FIFOLOG_FLG_4BYTE	0x02
#define FIFOLOG_FLG_RESTART	0x40
#define FIFOLOG_FLG_SYNC	0x80

#define FIFOLOG_TIMESTAMP	0x80000000
#define FIFOLOG_LENGTH		0x40000000
#define FIFOLOG_IDENT		0x3fffffff

#endif /* __LOCAL_FIFOLOG_H_ */