1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause 3 * 4 * Copyright (c) 2005-2008 Poul-Henning Kamp 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #ifndef __LOCAL_FIFOLOG_H_ 30 #define __LOCAL_FIFOLOG_H_ 31 32 /* 33 * Definitions for fifolog "protocol": the on-media layout. 34 * 35 * The fifolog on-media record has three layers: 36 * The outer timestamping and synchronization layer. 37 * The zlib implemented data compression. 38 * The inner sequencing and identification layer. 39 * 40 * All three layers are synchronized at a subset of the outer layer 41 * record boundaries, from where reading can be initiated. 42 * 43 * 44 * The outer layer: 45 * ----------------- 46 * The first record in a fifolog contains a magic string and version 47 * information along with a 32be encoded recordsize for all records 48 * in the fifolog, including the first. 49 * The recordsize is explicit to avoid ambiguities when a media is 50 * moved from one machine to another. 51 * 52 * Each record in the fifolog has the following contents: 53 * offset type contents 54 * -------------------------------------------------------------- 55 * 0 32be sequence_number 56 * The sequence number is randomly chosen for the 57 * fifolog and increments once for each record written. 58 * It's presence allow quick identification of the next 59 * record to be written using a binary search for the 60 * first place where a discontinuity in the sequence 61 * numbers occur. 62 * 4 8 flags (FIFOLOG_FLG_*) 63 * 64 * If (flags & (FIFOLOG_FLG_SYNC)) the record is a synchronization point 65 * at which the inner layers are aligned so that reading can be started 66 * at this point. 67 * To enable seeks into the file based on timestamps, a third field is 68 * present in these records as well: 69 * 5 32be time_t containing POSIX's understanding of UTC. 70 * 71 * These fields are immediately followed by the inner layer payload as 72 * described below, which has variable length. 73 * 74 * If the inner layer payload is shorter than the available space in 75 * the record, it is padded with zero bytes, and the number of unused 76 * bytes, including the encoded length thereof is recorded at the end 77 * of the record as follows: 78 * 79 * If (flags & FIFOLOG_FLG_1BYTE) 80 * n-1 8 number of unused bytes 81 * else if (flags & FIFOLOG_FLG_4BYTE) 82 * n-4 32be number of unused bytes 83 * 84 * 85 * The gzip layer 86 * -------------- 87 * Is just output from zlib, nothing special here. FIFOLOG_FLG_SYNC 88 * corresponds to Z_FINISH flags to zlib. 89 * In most cases, the timer will expire before zlib has filled an entire 90 * record in which case Z_SYNC_FLUSH will be used to force as much as 91 * possible into the buffer before it is written. This is not marked 92 * in outer layer (apart from a natural correlation with padding) since 93 * zlibs data stream handles this without help. 94 * 95 * 96 * The inner layer: 97 * ---------------- 98 * The inner layer contains data identification and to the second 99 * timestamping (the timestamp in the outer layer only marks the 100 * first possible timestamp for content in the SYNC record). 101 * 102 * offset type contents 103 * -------------------------------------------------------------- 104 * 0 32be ident 105 * 106 * The bottom 30 bits of the identification word are application defined, 107 * presently unused in the stand-alone fifolog tools, but used in the 108 * original "measured" application that originated the fifolog format. 109 * Should for instance syslogd(8) grow native support for fifolog format, 110 * it could store the message priority here. 111 * 112 * If (ident & FIFOLOG_TIMESTAMP) the record is prefixed by: 113 * 4 32be time_t containing POSIX's understanding of UTC. 114 * 115 * Then follows the content, either as a NUL terminated string or as 116 * a length encoded binary sequence: 117 * 118 * If (ident & FIFOLOG_LENGTH) the record is prefixed by: 119 * {0|4} 8 length of binary data 120 * 121 */ 122 123 /* Magic identification string */ 124 #define FIFOLOG_FMT_MAGIC "Measured FIFOLOG Ver 1.01\n" 125 126 /* Offset of the 32be encoded recordsize in the first sector */ 127 #define FIFOLOG_OFF_BS 0x20 128 129 #define FIFOLOG_FLG_1BYTE 0x01 130 #define FIFOLOG_FLG_4BYTE 0x02 131 #define FIFOLOG_FLG_RESTART 0x40 132 #define FIFOLOG_FLG_SYNC 0x80 133 134 #define FIFOLOG_TIMESTAMP 0x80000000 135 #define FIFOLOG_LENGTH 0x40000000 136 #define FIFOLOG_IDENT 0x3fffffff 137 138 #endif /* __LOCAL_FIFOLOG_H_ */ 139