139 lines
5.4 KiB
C
139 lines
5.4 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause
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*
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* Copyright (c) 2005-2008 Poul-Henning Kamp
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#ifndef __LOCAL_FIFOLOG_H_
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#define __LOCAL_FIFOLOG_H_
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/*
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* Definitions for fifolog "protocol": the on-media layout.
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*
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* The fifolog on-media record has three layers:
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* The outer timestamping and synchronization layer.
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* The zlib implemented data compression.
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* The inner sequencing and identification layer.
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*
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* All three layers are synchronized at a subset of the outer layer
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* record boundaries, from where reading can be initiated.
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*
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*
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* The outer layer:
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* -----------------
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* The first record in a fifolog contains a magic string and version
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* information along with a 32be encoded recordsize for all records
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* in the fifolog, including the first.
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* The recordsize is explicit to avoid ambiguities when a media is
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* moved from one machine to another.
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*
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* Each record in the fifolog has the following contents:
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* offset type contents
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* --------------------------------------------------------------
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* 0 32be sequence_number
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* The sequence number is randomly chosen for the
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* fifolog and increments once for each record written.
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* It's presence allow quick identification of the next
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* record to be written using a binary search for the
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* first place where a discontinuity in the sequence
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* numbers occur.
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* 4 8 flags (FIFOLOG_FLG_*)
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*
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* If (flags & (FIFOLOG_FLG_SYNC)) the record is a synchronization point
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* at which the inner layers are aligned so that reading can be started
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* at this point.
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* To enable seeks into the file based on timestamps, a third field is
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* present in these records as well:
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* 5 32be time_t containing POSIX's understanding of UTC.
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*
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* These fields are immediately followed by the inner layer payload as
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* described below, which has variable length.
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*
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* If the inner layer payload is shorter than the available space in
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* the record, it is padded with zero bytes, and the number of unused
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* bytes, including the encoded length thereof is recorded at the end
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* of the record as follows:
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*
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* If (flags & FIFOLOG_FLG_1BYTE)
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* n-1 8 number of unused bytes
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* else if (flags & FIFOLOG_FLG_4BYTE)
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* n-4 32be number of unused bytes
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*
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*
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* The gzip layer
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* --------------
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* Is just output from zlib, nothing special here. FIFOLOG_FLG_SYNC
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* corresponds to Z_FINISH flags to zlib.
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* In most cases, the timer will expire before zlib has filled an entire
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* record in which case Z_SYNC_FLUSH will be used to force as much as
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* possible into the buffer before it is written. This is not marked
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* in outer layer (apart from a natural correlation with padding) since
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* zlibs data stream handles this without help.
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*
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*
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* The inner layer:
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* ----------------
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* The inner layer contains data identification and to the second
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* timestamping (the timestamp in the outer layer only marks the
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* first possible timestamp for content in the SYNC record).
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*
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* offset type contents
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* --------------------------------------------------------------
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* 0 32be ident
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*
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* The bottom 30 bits of the identification word are application defined,
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* presently unused in the stand-alone fifolog tools, but used in the
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* original "measured" application that originated the fifolog format.
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* Should for instance syslogd(8) grow native support for fifolog format,
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* it could store the message priority here.
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*
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* If (ident & FIFOLOG_TIMESTAMP) the record is prefixed by:
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* 4 32be time_t containing POSIX's understanding of UTC.
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*
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* Then follows the content, either as a NUL terminated string or as
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* a length encoded binary sequence:
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*
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* If (ident & FIFOLOG_LENGTH) the record is prefixed by:
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* {0|4} 8 length of binary data
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*
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*/
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/* Magic identification string */
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#define FIFOLOG_FMT_MAGIC "Measured FIFOLOG Ver 1.01\n"
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/* Offset of the 32be encoded recordsize in the first sector */
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#define FIFOLOG_OFF_BS 0x20
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#define FIFOLOG_FLG_1BYTE 0x01
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#define FIFOLOG_FLG_4BYTE 0x02
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#define FIFOLOG_FLG_RESTART 0x40
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#define FIFOLOG_FLG_SYNC 0x80
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#define FIFOLOG_TIMESTAMP 0x80000000
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#define FIFOLOG_LENGTH 0x40000000
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#define FIFOLOG_IDENT 0x3fffffff
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#endif /* __LOCAL_FIFOLOG_H_ */
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