2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2005-2008 Poul-Henning Kamp
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31 #ifndef __LOCAL_FIFOLOG_H_
32 #define __LOCAL_FIFOLOG_H_
35 * Definitions for fifolog "protocol": the on-media layout.
37 * The fifolog on-media record has three layers:
38 * The outer timestamping and synchronization layer.
39 * The zlib implemented data compression.
40 * The inner sequencing and identification layer.
42 * All three layers are synchronized at a subset of the outer layer
43 * record boundaries, from where reading can be initiated.
48 * The first record in a fifolog contains a magic string and version
49 * information along with a 32be encoded recordsize for all records
50 * in the fifolog, including the first.
51 * The recordsize is explicit to avoid ambiguities when a media is
52 * moved from one machine to another.
54 * Each record in the fifolog has the following contents:
55 * offset type contents
56 * --------------------------------------------------------------
57 * 0 32be sequence_number
58 * The sequence number is randomly chosen for the
59 * fifolog and increments once for each record written.
60 * It's presence allow quick identification of the next
61 * record to be written using a binary search for the
62 * first place where a discontinuity in the sequence
64 * 4 8 flags (FIFOLOG_FLG_*)
66 * If (flags & (FIFOLOG_FLG_SYNC)) the record is a synchronization point
67 * at which the inner layers are aligned so that reading can be started
69 * To enable seeks into the file based on timestamps, a third field is
70 * present in these records as well:
71 * 5 32be time_t containing POSIX's understanding of UTC.
73 * These fields are immediately followed by the inner layer payload as
74 * described below, which has variable length.
76 * If the inner layer payload is shorter than the available space in
77 * the record, it is padded with zero bytes, and the number of unused
78 * bytes, including the encoded length thereof is recorded at the end
79 * of the record as follows:
81 * If (flags & FIFOLOG_FLG_1BYTE)
82 * n-1 8 number of unused bytes
83 * else if (flags & FIFOLOG_FLG_4BYTE)
84 * n-4 32be number of unused bytes
89 * Is just output from zlib, nothing special here. FIFOLOG_FLG_SYNC
90 * corresponds to Z_FINISH flags to zlib.
91 * In most cases, the timer will expire before zlib has filled an entire
92 * record in which case Z_SYNC_FLUSH will be used to force as much as
93 * possible into the buffer before it is written. This is not marked
94 * in outer layer (apart from a natural correlation with padding) since
95 * zlibs data stream handles this without help.
100 * The inner layer contains data identification and to the second
101 * timestamping (the timestamp in the outer layer only marks the
102 * first possible timestamp for content in the SYNC record).
104 * offset type contents
105 * --------------------------------------------------------------
108 * The bottom 30 bits of the identification word are application defined,
109 * presently unused in the stand-alone fifolog tools, but used in the
110 * original "measured" application that originated the fifolog format.
111 * Should for instance syslogd(8) grow native support for fifolog format,
112 * it could store the message priority here.
114 * If (ident & FIFOLOG_TIMESTAMP) the record is prefixed by:
115 * 4 32be time_t containing POSIX's understanding of UTC.
117 * Then follows the content, either as a NUL terminated string or as
118 * a length encoded binary sequence:
120 * If (ident & FIFOLOG_LENGTH) the record is prefixed by:
121 * {0|4} 8 length of binary data
125 /* Magic identification string */
126 #define FIFOLOG_FMT_MAGIC "Measured FIFOLOG Ver 1.01\n"
128 /* Offset of the 32be encoded recordsize in the first sector */
129 #define FIFOLOG_OFF_BS 0x20
131 #define FIFOLOG_FLG_1BYTE 0x01
132 #define FIFOLOG_FLG_4BYTE 0x02
133 #define FIFOLOG_FLG_RESTART 0x40
134 #define FIFOLOG_FLG_SYNC 0x80
136 #define FIFOLOG_TIMESTAMP 0x80000000
137 #define FIFOLOG_LENGTH 0x40000000
138 #define FIFOLOG_IDENT 0x3fffffff
140 #endif /* __LOCAL_FIFOLOG_H_ */