ltt/branches/poly/doc/developer/format.html

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   4   <title>The new LTT trace format</title>
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   6   <body>
   7
   8 <h1>The new LTT trace format</h1>
   9
  10 <P>
  11 A trace is contained in a directory tree. To send a trace remotely,
  12 the directory tree may be tar-gzipped. Trace foo, placed in the home
  13 directory of user john, /home/john, would have the following content:
  14
  15 <PRE><TT>
  16 $ cd /home/john
  17 $ tree foo
  18 foo/
  19 |-- eventdefs
  20 |   |-- core.xml
  21 |   |-- net.xml
  22 |   |-- ipv4.xml
  23 |   `-- ide.xml
  24 |-- info
  25 |   |-- bookmarks.xml
  26 |   `-- system.xml
  27 |-- control
  28 |   |-- facilities
  29 |   |-- interrupts
  30 |   `-- processes
  31 `-- cpu
  32     |-- 0
  33     |-- 1
  34     |-- 2
  35     `-- 3
  36 </TT></PRE>
  37
  38 <P>
  39 The eventdefs directory contains the events descriptions for all the
  40 facilities used. The syntax is a simple subset of XML; XML is widely
  41 known and easily parsed or hand edited. Each file contains one or more
  42 <FACILITY NAME=name>...</FACILITY> elements. Indeed, several
  43 facilities may have the same name but different content (and thus will
  44 generate a different checksum), typically when the event descriptions
  45 for a given facility change from one version to the next, if a module
  46 is recompiled and reloaded during a trace.
  47
  48 <P>
  49 A small number of events are predefined, part of the "builtin" facility,
  50 and are not present there. These "builtin" events include "facility_load",
  51 "block_start", "block_end" and "time_heartbeat".
  52
  53 <P>
  54 The cpu directory contains a tracefile for each cpu, numbered from 0,
  55 in .trace format. A uniprocessor thus only contains the file cpu/0.
  56 A multi-processor with some unused (possibly hotplug) CPU slots may have some
  57 unused CPU numbers. For instance a 8 way SMP board with 6 CPUs randomly
  58 installed may produce tracefiles named 0, 1, 2, 4, 6, 7.
  59
  60 <P>
  61 The files in the control directory also follow the .trace format.
  62 The "facilities" file only contains "builtin" facility_load events
  63 and is used to determine the facilities used and the code range assigned
  64 to each facility. The other control files contain the initial system
  65 state and various subsequent important events, for example process
  66 creations and exit. The interest of placing such subsequent events
  67 in control trace files instead of (or in addition to) in the per cpu
  68 trace files is that they may be accessed more quickly/conveniently
  69 and that they may be kept even when the per cpu files are overwritten
  70 in "flight recorder mode".
  71
  72 <P>
  73 The info directory contains in system.xml a description of the system on which
  74 the trace was created as well as different user annotations in bookmark.xml.
  75 This directory may also contain various information about the trace, generated
  76 during trace analysis (statistics, index...).
  77
  78
  79 <H2>Trace format</H2>
  80
  81 <P>
  82 Each tracefile is divided into equal size blocks with an uint32 at the block
  83 end giving the offset to the last event in the block. Events are packed
  84 sequentially in the block starting at offset 0 with a "block_start" event
  85 and ending, at the offset stored in the last 4 bytes of the block, with a
  86 block_end event. Both the block_start and block_end events
  87 contain the kernel timestamp (timespec binary structure,
  88 uint32 seconds, uint32 nanoseconds), the cycle counter (uint64 cycles),
  89 and the buffer id (uint64).
  90
  91 <P>
  92 Each event consists in an event type id (uint16 which is the event type id
  93 within the facility + the facility base id), a time delta (uint32 in cycles
  94 or nanoseconds, depending on configuration, since the last time value, in the
  95 block header or in a "time_heartbeat" event) and the event type specific data.
  96 All values are packed in native byte order binary format.
  97
  98
  99 <H2>System description</H2>
 100
 101 <P>
 102 The system type description, in system.xml, looks like:
 103
 104 <PRE><TT>
 105 &lt;system
 106  node_name="vaucluse"
 107  domainname="polymtl.ca"
 108  cpu=4
 109  arch_size="ILP32"
 110  endian="little"
 111  kernel_name="Linux"
 112  kernel_release="2.4.18-686-smp"
 113  kernel_version="#1 SMP Sun Apr 14 12:07:19 EST 2002"
 114  machine="i686"
 115  processor="unknown"
 116  hardware_platform="unknown"
 117  operating_system="Linux"
 118  ltt_major_version="2"
 119  ltt_minor_version="0"
 120  ltt_block_size="100000"
 121 &gt;
 122 Some comments about the system
 123 &lt;/system&gt;
 124 </TT></PRE>
 125
 126 <P>
 127 The system attributes kernel_name, node_name, kernel_release,
 128  kernel_version, machine, processor, hardware_platform and operating_system
 129 come from the uname(1) program. The domainname attribute is obtained from
 130 the "hostname --domain" command. The arch_size attribute is one of
 131 LP32, ILP32, LP64 or ILP64 and specifies the length in bits of integers (I),
 132 long (L) and pointers (P). The endian attribute is "little" or "big".
 133 While the arch_size and endian attributes could be deduced from the platform
 134 type, having these explicit allows analysing traces from yet unknown
 135 platforms. The cpu attribute specifies the maximum number of processors in
 136 the system; only tracefiles 0 to this maximum - 1 may exist in the cpu
 137 directory.
 138
 139 <P>
 140 Within the system element, the text enclosed may describe further the
 141 system traced.
 142
 143
 144 <H2>Event type descriptions</H2>
 145
 146 <P>
 147 A facility contains the descriptions of several event types. When a structure
 148 is reused in several event types, a named type is defined and may be referenced
 149 by several other event types or named types.
 150
 151 <PRE><TT>
 152 &lt;facility name=facility_name&gt;
 153   &lt;description&gt;Some text&lt;/description&gt;
 154   &lt;event name=eventtype_name&gt;
 155     &lt;description&gt;Some text&lt;/description&gt;
 156     --type structure--
 157   &lt;/event&gt;
 158   ...
 159   &lt;type name=type_name&gt;
 160     --type structure--
 161   &lt;/type&gt;
 162 &lt;/facility&gt;
 163 </TT></PRE>
 164
 165 <P>
 166 The type structure may be one of the following primitive type elements.
 167 Whenever the keyword isize is used, the allowed values are
 168 short, medium, long, 1, 2, 4, 8, indicating the size in bytes.
 169 The fsize keyword represents one of medium, long, 4 and 8 bytes.
 170
 171 <PRE><TT>
 172 &lt;int size=isize format="printf format"/&gt;
 173
 174 &lt;uint size=isize format="printf format"/&gt;
 175
 176 &lt;float size=fsize format="printf format"/&gt;
 177
 178 &lt;string format="printf format"/&gt;
 179
 180 &lt;enum size=isize format="printf format"&gt;label1 label2 ...&lt;/enum&gt;
 181 </TT></PRE>
 182
 183 <P>
 184 The string is null terminated. For the enumeration, the size of the integer
 185 used for its representation is specified.
 186
 187 <P>
 188 The type structure may also be a compound type.
 189
 190 <PRE><TT>
 191 &lt;array size=n&gt; --type structure-- &lt;/array&gt;
 192
 193 &lt;sequence lengthsize=isize&gt; --type structure-- &lt;/sequence&gt;
 194
 195 &lt;struct&gt;
 196   &lt;field name=field_name&gt;
 197     &lt;description&gt;Some text&lt;/description&gt;
 198     --type structure--
 199   &lt;/field&gt;
 200   ...
 201 &lt;/struct&gt;
 202
 203 &lt;union typecodesize=isize&gt;
 204   &lt;field name=field_name&gt;
 205     &lt;description&gt;Some text&lt;/description&gt;
 206     --type structure--
 207   &lt;/field&gt;
 208   ...
 209 &lt;/union&gt;
 210 </TT></PRE>
 211
 212 <P>
 213 Array is a fixed size array of length size. Sequence is a variable size
 214 array with its length stored as a prepended uint of length lengthsize.
 215 A structure is simply an aggregation of fields. An union is one of its n
 216 fields (variant record), as indicated by a preceeding code (0 to n - 1)
 217 of the specified size typecodesize.
 218
 219 <P>
 220 Finally the type structure may be defined by referencing a named type.
 221
 222 <PRE><TT>
 223 &lt;typeref name=type_name/&gt;
 224 </PRE></TT>
 225
 226 <H2>Builtin events</H2>
 227
 228 <P>
 229 The facility named "builtin" is always present and contains at least the
 230 following event types.
 231
 232 <PRE><TT>
 233 &lt;event name=facility_load&gt;
 234   &lt;description&gt;Facility used in the trace&lt;/description&gt;
 235   &lt;struct&gt;
 236     &lt;field name="name"&gt;&lt;string/&gt;&lt;/field&gt;
 237     &lt;field name="checksum"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 238     &lt;field name="base_code"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 239   &lt;/struct&gt;
 240 &lt;/event&gt;
 241
 242 &lt;event name=block_start&gt;
 243   &lt;description&gt;Block start timestamp&lt;/description&gt;
 244   &lt;typeref name=block_timestamp/&gt;
 245 &lt;/event&gt;
 246
 247 &lt;event name=block_end&gt;
 248   &lt;description&gt;Block end timestamp&lt;/description&gt;
 249   &lt;typeref name=block_timestamp/&gt;
 250 &lt;/event&gt;
 251
 252 &lt;event name=time_heartbeat&gt;
 253   &lt;description&gt;System time values sent periodically to minimize cycle counter
 254     drift with respect to real time clock and to detect cycle counter
 255     rollovers
 256   &lt;/description&gt;
 257   &lt;typeref name=timestamp/&gt;
 258 &lt;/event&gt;
 259
 260 &lt;type name=block_timestamp&gt;
 261   &lt;struct&gt;
 262     &lt;field name=timestamp&gt;&lt;typeref name=timestamp&gt;&lt;/field&gt;
 263     &lt;field name=block_id&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 264   &lt;/struct&gt;
 265 &lt;/type&gt;
 266
 267 &lt;type name=timestamp&gt;
 268   &lt;struct&gt;
 269     &lt;field name=time&gt;&lt;typeref name=timespec/&gt;&lt;/event&gt;
 270     &lt;field name="cycle_count"&gt;&lt;uint size=8/&gt;&lt;/field&gt;
 271   &lt;/struct&gt;
 272 &lt;/event&gt;
 273
 274 &lt;type name=timespec&gt;
 275   &lt;struct&gt;
 276     &lt;field name="seconds"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 277     &lt;field name="nanoseconds"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 278   &lt;/struct&gt;
 279 &lt;/type&gt;
 280 </TT></PRE>
 281
 282 <H2>Control files</H2>
 283
 284 <P>
 285 The interrupts file reflects the content of the /proc/interrupts system file.
 286 It contains one event describing each interrupt. At trace start, events are
 287 generated describing all the current interrupts. If the assignment of
 288 interrupts changes later, due to devices or device drivers being activated or
 289 deactivated, additional events may be added to the file. Each interrupt
 290 event has the following structure.
 291
 292 <PRE><TT>
 293 &lt;event name=interrupt&gt;
 294   &lt;description&gt;Interrupt request number assignment&lt;description&gt;
 295   &lt;struct&gt;
 296     &lt;field name="number"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 297     &lt;field name="count"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 298     &lt;field name="controller"&gt;&lt;string/&gt;&lt;/field&gt;
 299     &lt;field name="name"&gt;&lt;string/&gt;&lt;/field&gt;
 300   &lt;/struct&gt;
 301 &lt;/event&gt;
 302 </TT></PRE>
 303
 304 <P>
 305 The processes file contains the list of processes already created when the
 306 trace starts. Each process describing event is modeled after the
 307 /proc/self/status system file. The number of fields in this event is
 308 expected to be expanded in the future to include groups, signal masks,
 309 opened file descriptors and address maps.
 310
 311 <PRE><TT>
 312 &lt;event name=process&gt;
 313   &lt;description&gt;Existing process&lt;description&gt;
 314   &lt;struct&gt;
 315     &lt;field name="name"&gt;&lt;string/&gt;&lt;/field&gt;
 316     &lt;field name="pid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 317     &lt;field name="ppid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 318     &lt;field name="tracer_pid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 319     &lt;field name="uid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 320     &lt;field name="euid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 321     &lt;field name="suid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 322     &lt;field name="fsuid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 323     &lt;field name="gid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 324     &lt;field name="egid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 325     &lt;field name="sgid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 326     &lt;field name="fsgid"&gt;&lt;uint size=4/&gt;&lt;/field&gt;
 327     &lt;field name="state"&gt;&lt;enum size=4&gt;
 328         Running WaitInterruptible WaitUninterruptible Zombie Traced Paging
 329     &lt;/enum&gt;&lt;/field&gt;
 330   &lt;/struct&gt;
 331 &lt;/event&gt;
 332 </TT></PRE>
 333
 334 <H2>Facilities</H2>
 335
 336 <P>
 337 Facilities define a granularity of events grouping for filtering, activation
 338 and compilation. Each facility does cost a table entry in the kernel (name,
 339 checksum, event type code range), or somewhere between 20 and 30 bytes. Having
 340 one facility per tracing statement in the kernel would be too much (assuming
 341 that they eventually are routinely inserted in the kernel code and replace
 342 the 80000+ printk statements in some proportion). However, having a few
 343 facilities, up to a few tens, would make sense.
 344
 345 <P>
 346 The "builtin" facility contains a small number of predefined events which must
 347 always exist. The "core" facility contains a small subset of OS events which
 348 are almost always of interest (scheduling, interrupts, faults, system calls).
 349 Then, specialized facilities may exist for each subsystem (network, disks,
 350 USB, SCSI...).
 351
 352
 353 <H2>Bookmarks</H2>
 354
 355 <P>
 356 Bookmarks are user supplied information added to a trace. They contain user
 357 annotations attached to a time interval.
 358
 359 <PRE><TT>
 360 &lt;bookmarks&gt;
 361   &lt;location name=name cpu=n start_time=t end_time=t&gt;Some text&lt;/location&gt;
 362   ...
 363 &lt;/bookmarks&gt;
 364 </TT></PRE>
 365
 366 <P>
 367 The interval is defined using either "time=" or "start_time=" and
 368 "end_time=", or "cycle=" or "start_cycle=" and "end_cycle=".
 369 The time is in seconds with decimals up to nanoseconds and cycle counts
 370 are unsigned integers with a 64 bits range. The cpu attribute is optional.
 371
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