2 * Copyright (c) 2005-2008 Poul-Henning Kamp
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29 #ifndef __LOCAL_FIFOLOG_H_
30 #define __LOCAL_FIFOLOG_H_
33 * Definitions for fifolog "protocol": the on-media layout.
35 * The fifolog on-media record has three layers:
36 * The outher timestamping and synchronization layer.
37 * The zlib implemented data compression
38 * The inner sequencing and identification layer.
40 * All three layers are synchronized at a subset of the outher layer
41 * record boundaries, from where reading can be initiated.
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.
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 precense 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
62 * 4 8 flags (FIFOLOG_FLG_*)
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
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.
71 * These fields are immediately followed by the inner layer payload as
72 * described below, which has variable length.
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:
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
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 outher layer (apart from a natural correlation with padding) since
93 * zlibs data stream handles this without help.
98 * The inner layer contains data indentification and to the second
99 * timestamping (the timestamp in the outherlayer only marks the
100 * first possible timestamp for content in the SYNC record).
102 * offset type contents
103 * --------------------------------------------------------------
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.
112 * If (ident & FIFOLOG_TIMESTAMP) the record is prefixed by:
113 * 4 32be time_t containing POSIX's understanding of UTC.
115 * Then follows the content, either as a NUL terminated string or as
116 * a lenght encoded binary sequence:
118 * If (ident & FIFOLOG_LENGTH) the record is prefixed by:
119 * {0|4} 8 length of binary data
123 /* Magic identification string */
124 #define FIFOLOG_FMT_MAGIC "Measured FIFOLOG Ver 1.01\n"
126 /* Offset of the 32be encoded recordsize in the first sector */
127 #define FIFOLOG_OFF_BS 0x20
129 #define FIFOLOG_FLG_1BYTE 0x01
130 #define FIFOLOG_FLG_4BYTE 0x02
131 #define FIFOLOG_FLG_RESTART 0x40
132 #define FIFOLOG_FLG_SYNC 0x80
134 #define FIFOLOG_TIMESTAMP 0x80000000
135 #define FIFOLOG_LENGTH 0x40000000
136 #define FIFOLOG_IDENT 0x3fffffff
138 #endif /* __LOCAL_FIFOLOG_H_ */