update to enum
[ctf.git] / common-trace-format-proposal.txt
CommitLineData
5ba9f198 1
4767a9e7 2RFC: Common Trace Format (CTF) Proposal (pre-v1.7)
5ba9f198
MD
3
4Mathieu Desnoyers, EfficiOS Inc.
5
6The goal of the present document is to propose a trace format that suits the
cc089c3a 7needs of the embedded, telecom, high-performance and kernel communities. It is
5ba9f198 8based on the Common Trace Format Requirements (v1.4) document. It is designed to
cc089c3a
MD
9allow traces to be natively generated by the Linux kernel, Linux user-space
10applications written in C/C++, and hardware components.
11
12The latest version of this document can be found at:
13
14 git tree: git://git.efficios.com/ctf.git
15 gitweb: http://git.efficios.com/?p=ctf.git
5ba9f198
MD
16
17A reference implementation of a library to read and write this trace format is
18being implemented within the BabelTrace project, a converter between trace
19formats. The development tree is available at:
20
21 git tree: git://git.efficios.com/babeltrace.git
22 gitweb: http://git.efficios.com/?p=babeltrace.git
23
24
251. Preliminary definitions
26
3bf79539
MD
27 - Event Trace: An ordered sequence of events.
28 - Event Stream: An ordered sequence of events, containing a subset of the
29 trace event types.
30 - Event Packet: A sequence of physically contiguous events within an event
31 stream.
5ba9f198
MD
32 - Event: This is the basic entry in a trace. (aka: a trace record).
33 - An event identifier (ID) relates to the class (a type) of event within
3bf79539
MD
34 an event stream.
35 e.g. event: irq_entry.
5ba9f198
MD
36 - An event (or event record) relates to a specific instance of an event
37 class.
3bf79539
MD
38 e.g. event: irq_entry, at time X, on CPU Y
39 - Source Architecture: Architecture writing the trace.
40 - Reader Architecture: Architecture reading the trace.
5ba9f198
MD
41
42
432. High-level representation of a trace
44
3bf79539
MD
45A trace is divided into multiple event streams. Each event stream contains a
46subset of the trace event types.
5ba9f198 47
3bf79539
MD
48The final output of the trace, after its generation and optional transport over
49the network, is expected to be either on permanent or temporary storage in a
50virtual file system. Because each event stream is appended to while a trace is
51being recorded, each is associated with a separate file for output. Therefore,
52a stored trace can be represented as a directory containing one file per stream.
5ba9f198 53
3bf79539 54A metadata event stream contains information on trace event types. It describes:
5ba9f198
MD
55
56- Trace version.
57- Types available.
3bf79539
MD
58- Per-stream event header description.
59- Per-stream event header selection.
60- Per-stream event context fields.
5ba9f198 61- Per-event
3bf79539 62 - Event type to stream mapping.
5ba9f198
MD
63 - Event type to name mapping.
64 - Event type to ID mapping.
65 - Event fields description.
66
67
3bf79539 683. Event stream
5ba9f198 69
3bf79539
MD
70An event stream is divided in contiguous event packets of variable size. These
71subdivisions have a variable size. An event packet can contain a certain amount
72of padding at the end. The rationale for the event stream design choices is
73explained in Appendix B. Stream Header Rationale.
5ba9f198 74
3bf79539
MD
75An event stream is divided in contiguous event packets of variable size. These
76subdivisions have a variable size. An event packet can contain a certain amount
77of padding at the end. The stream header is repeated at the beginning of each
78event packet.
5ba9f198 79
3bf79539
MD
80The event stream header will therefore be referred to as the "event packet
81header" throughout the rest of this document.
5ba9f198
MD
82
83
844. Types
85
864.1 Basic types
87
88A basic type is a scalar type, as described in this section.
89
904.1.1 Type inheritance
91
80fd2569
MD
92Type specifications can be inherited to allow deriving types from a
93type class. For example, see the uint32_t named type derived from the "integer"
94type class below ("Integers" section). Types have a precise binary
95representation in the trace. A type class has methods to read and write these
96types, but must be derived into a type to be usable in an event field.
5ba9f198
MD
97
984.1.2 Alignment
99
100We define "byte-packed" types as aligned on the byte size, namely 8-bit.
101We define "bit-packed" types as following on the next bit, as defined by the
102"bitfields" section.
5ba9f198 103
3bf79539
MD
104All basic types, except bitfields, are either aligned on an architecture-defined
105specific alignment or byte-packed, depending on the architecture preference.
106Architectures providing fast unaligned write byte-packed basic types to save
5ba9f198 107space, aligning each type on byte boundaries (8-bit). Architectures with slow
3bf79539
MD
108unaligned writes align types on specific alignment values. If no specific
109alignment is declared for a type nor its parents, it is assumed to be bit-packed
110for bitfields and byte-packed for other types.
5ba9f198 111
3bf79539 112Metadata attribute representation of a specific alignment:
5ba9f198
MD
113
114 align = value; /* value in bits */
115
1164.1.3 Byte order
117
3bf79539
MD
118By default, the native endianness of the source architecture the trace is used.
119Byte order can be overridden for a basic type by specifying a "byte_order"
120attribute. Typical use-case is to specify the network byte order (big endian:
121"be") to save data captured from the network into the trace without conversion.
122If not specified, the byte order is native.
5ba9f198
MD
123
124Metadata representation:
125
126 byte_order = native OR network OR be OR le; /* network and be are aliases */
127
1284.1.4 Size
129
130Type size, in bits, for integers and floats is that returned by "sizeof()" in C
131multiplied by CHAR_BIT.
132We require the size of "char" and "unsigned char" types (CHAR_BIT) to be fixed
133to 8 bits for cross-endianness compatibility.
134
135Metadata representation:
136
137 size = value; (value is in bits)
138
1394.1.5 Integers
140
141Signed integers are represented in two-complement. Integer alignment, size,
142signedness and byte ordering are defined in the metadata. Integers aligned on
143byte size (8-bit) and with length multiple of byte size (8-bit) correspond to
144the C99 standard integers. In addition, integers with alignment and/or size that
145are _not_ a multiple of the byte size are permitted; these correspond to the C99
146standard bitfields, with the added specification that the CTF integer bitfields
147have a fixed binary representation. A MIT-licensed reference implementation of
148the CTF portable bitfields is available at:
149
150 http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h
151
152Binary representation of integers:
153
154- On little and big endian:
155 - Within a byte, high bits correspond to an integer high bits, and low bits
156 correspond to low bits.
157- On little endian:
158 - Integer across multiple bytes are placed from the less significant to the
159 most significant.
160 - Consecutive integers are placed from lower bits to higher bits (even within
161 a byte).
162- On big endian:
163 - Integer across multiple bytes are placed from the most significant to the
164 less significant.
165 - Consecutive integers are placed from higher bits to lower bits (even within
166 a byte).
167
168This binary representation is derived from the bitfield implementation in GCC
169for little and big endian. However, contrary to what GCC does, integers can
170cross units boundaries (no padding is required). Padding can be explicitely
171added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed.
172
173Metadata representation:
174
80fd2569 175 integer {
5ba9f198
MD
176 signed = true OR false; /* default false */
177 byte_order = native OR network OR be OR le; /* default native */
178 size = value; /* value in bits, no default */
179 align = value; /* value in bits */
2152348f 180 }
5ba9f198 181
80fd2569 182Example of type inheritance (creation of a uint32_t named type):
5ba9f198 183
80fd2569 184typedef integer {
9e4e34e9 185 size = 32;
5ba9f198
MD
186 signed = false;
187 align = 32;
80fd2569 188} uint32_t;
5ba9f198 189
80fd2569 190Definition of a named 5-bit signed bitfield:
5ba9f198 191
80fd2569 192typedef integer {
5ba9f198
MD
193 size = 5;
194 signed = true;
195 align = 1;
80fd2569 196} int5_t;
5ba9f198
MD
197
1984.1.6 GNU/C bitfields
199
200The GNU/C bitfields follow closely the integer representation, with a
201particularity on alignment: if a bitfield cannot fit in the current unit, the
80fd2569
MD
202unit is padded and the bitfield starts at the following unit. The unit size is
203defined by the size of the type "unit_type".
5ba9f198 204
2152348f 205Metadata representation:
80fd2569
MD
206
207 unit_type name:size:
208
5ba9f198
MD
209As an example, the following structure declared in C compiled by GCC:
210
211struct example {
212 short a:12;
213 short b:5;
214};
215
2152348f
MD
216The example structure is aligned on the largest element (short). The second
217bitfield would be aligned on the next unit boundary, because it would not fit in
218the current unit.
5ba9f198
MD
219
2204.1.7 Floating point
221
222The floating point values byte ordering is defined in the metadata.
223
224Floating point values follow the IEEE 754-2008 standard interchange formats.
225Description of the floating point values include the exponent and mantissa size
226in bits. Some requirements are imposed on the floating point values:
227
228- FLT_RADIX must be 2.
229- mant_dig is the number of digits represented in the mantissa. It is specified
230 by the ISO C99 standard, section 5.2.4, as FLT_MANT_DIG, DBL_MANT_DIG and
231 LDBL_MANT_DIG as defined by <float.h>.
232- exp_dig is the number of digits represented in the exponent. Given that
233 mant_dig is one bit more than its actual size in bits (leading 1 is not
234 needed) and also given that the sign bit always takes one bit, exp_dig can be
235 specified as:
236
237 - sizeof(float) * CHAR_BIT - FLT_MANT_DIG
238 - sizeof(double) * CHAR_BIT - DBL_MANT_DIG
239 - sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG
240
241Metadata representation:
242
80fd2569 243floating_point {
5ba9f198
MD
244 exp_dig = value;
245 mant_dig = value;
246 byte_order = native OR network OR be OR le;
2152348f 247}
5ba9f198
MD
248
249Example of type inheritance:
250
80fd2569 251typedef floating_point {
5ba9f198
MD
252 exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
253 mant_dig = 24; /* FLT_MANT_DIG */
254 byte_order = native;
80fd2569 255} float;
5ba9f198
MD
256
257TODO: define NaN, +inf, -inf behavior.
258
2594.1.8 Enumerations
260
261Enumerations are a mapping between an integer type and a table of strings. The
262numerical representation of the enumeration follows the integer type specified
263by the metadata. The enumeration mapping table is detailed in the enumeration
3bf79539
MD
264description within the metadata. The mapping table maps inclusive value ranges
265(or single values) to strings. Instead of being limited to simple
266"value -> string" mappings, these enumerations map
80fd2569 267"[ start_value ... end_value ] -> string", which map inclusive ranges of
3bf79539
MD
268values to strings. An enumeration from the C language can be represented in
269this format by having the same start_value and end_value for each element, which
270is in fact a range of size 1. This single-value range is supported without
4767a9e7 271repeating the start and end values with the value = string declaration.
80fd2569 272
4767a9e7
MD
273If a numeric value is encountered between < >, it represents the integer type
274size used to hold the enumeration, in bits.
275
276enum <integer_type OR size> name {
80fd2569
MD
277 string = start_value1 ... end_value1,
278 "other string" = start_value2 ... end_value2,
279 yet_another_string, /* will be assigned to end_value2 + 1 */
280 "some other string" = value,
281 ...
282};
283
284If the values are omitted, the enumeration starts at 0 and increment of 1 for
285each entry:
286
4767a9e7 287enum <32> name {
80fd2569
MD
288 ZERO,
289 ONE,
290 TWO,
291 TEN = 10,
292 ELEVEN,
3bf79539 293};
5ba9f198 294
80fd2569 295Overlapping ranges within a single enumeration are implementation defined.
5ba9f198 296
2152348f
MD
297A nameless enumeration can be declared as a field type or as part of a typedef:
298
299enum <integer_type> {
300 ...
301}
302
5ba9f198
MD
3034.2 Compound types
304
3054.2.1 Structures
306
307Structures are aligned on the largest alignment required by basic types
308contained within the structure. (This follows the ISO/C standard for structures)
309
80fd2569 310Metadata representation of a named structure:
5ba9f198 311
80fd2569
MD
312struct name {
313 field_type field_name;
314 field_type field_name;
315 ...
316};
5ba9f198
MD
317
318Example:
319
80fd2569
MD
320struct example {
321 integer { /* Nameless type */
322 size = 16;
323 signed = true;
324 align = 16;
325 } first_field_name;
326 uint64_t second_field_name; /* Named type declared in the metadata */
3bf79539 327};
5ba9f198
MD
328
329The fields are placed in a sequence next to each other. They each possess a
330field name, which is a unique identifier within the structure.
331
2152348f 332A nameless structure can be declared as a field type or as part of a typedef:
80fd2569
MD
333
334struct {
335 ...
2152348f 336}
80fd2569 337
5ba9f198
MD
3384.2.2 Arrays
339
340Arrays are fixed-length. Their length is declared in the type declaration within
341the metadata. They contain an array of "inner type" elements, which can refer to
342any type not containing the type of the array being declared (no circular
3bf79539 343dependency). The length is the number of elements in an array.
5ba9f198 344
2152348f 345Metadata representation of a named array:
80fd2569
MD
346
347typedef elem_type name[length];
5ba9f198 348
2152348f 349A nameless array can be declared as a field type within a structure, e.g.:
5ba9f198 350
2152348f 351 uint8_t field_name[10];
80fd2569 352
5ba9f198
MD
353
3544.2.3 Sequences
355
356Sequences are dynamically-sized arrays. They start with an integer that specify
357the length of the sequence, followed by an array of "inner type" elements.
3bf79539 358The length is the number of elements in the sequence.
5ba9f198 359
2152348f 360Metadata representation for a named sequence:
80fd2569
MD
361
362typedef elem_type name[length_type];
363
364A nameless sequence can be declared as a field type, e.g.:
365
80fd2569
MD
366long field_name[int];
367
368The length type follows the integer types specifications, and the sequence
5ba9f198
MD
369elements follow the "array" specifications.
370
3714.2.4 Strings
372
373Strings are an array of bytes of variable size and are terminated by a '\0'
374"NULL" character. Their encoding is described in the metadata. In absence of
375encoding attribute information, the default encoding is UTF-8.
376
80fd2569
MD
377Metadata representation of a named string type:
378
379typedef string {
5ba9f198 380 encoding = UTF8 OR ASCII;
80fd2569 381} name;
5ba9f198 382
80fd2569
MD
383A nameless string type can be declared as a field type:
384
385string field_name; /* Use default UTF8 encoding */
5ba9f198 386
3bf79539
MD
3875. Event Packet Header
388
389The event packet header consists of two part: one is mandatory and have a fixed
390layout. The second part, the "event packet context", has its layout described in
391the metadata.
5ba9f198 392
3bf79539
MD
393- Aligned on page size. Fixed size. Fields either aligned or packed (depending
394 on the architecture preference).
395 No padding at the end of the event packet header. Native architecture byte
5ba9f198 396 ordering.
3bf79539
MD
397
398Fixed layout (event packet header):
399
5ba9f198
MD
400- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
401 representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
402 representation. Used to distinguish between big and little endian traces (this
403 information is determined by knowing the endianness of the architecture
404 reading the trace and comparing the magic number against its value and the
405 reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
406 description language described in this document. Different magic numbers
407 should be used for other metadata description languages.
3bf79539 408- Trace UUID, used to ensure the event packet match the metadata used.
5ba9f198
MD
409 (note: we cannot use a metadata checksum because metadata can be appended to
410 while tracing is active)
3bf79539
MD
411- Stream ID, used as reference to stream description in metadata.
412
413Metadata-defined layout (event packet context):
414
415- Event packet content size (in bytes).
416- Event packet size (in bytes, includes padding).
417- Event packet content checksum (optional). Checksum excludes the event packet
418 header.
419- Per-stream event packet sequence count (to deal with UDP packet loss). The
420 number of significant sequence counter bits should also be present, so
421 wrap-arounds are deal with correctly.
422- Timestamp at the beginning and timestamp at the end of the event packet.
423 Both timestamps are written in the packet header, but sampled respectively
424 while (or before) writing the first event and while (or after) writing the
425 last event in the packet. The inclusive range between these timestamps should
426 include all event timestamps assigned to events contained within the packet.
5ba9f198 427- Events discarded count
3bf79539
MD
428 - Snapshot of a per-stream free-running counter, counting the number of
429 events discarded that were supposed to be written in the stream prior to
430 the first event in the event packet.
5ba9f198 431 * Note: producer-consumer buffer full condition should fill the current
3bf79539 432 event packet with padding so we know exactly where events have been
5ba9f198 433 discarded.
3bf79539
MD
434- Lossless compression scheme used for the event packet content. Applied
435 directly to raw data. New types of compression can be added in following
436 versions of the format.
5ba9f198
MD
437 0: no compression scheme
438 1: bzip2
439 2: gzip
3bf79539
MD
440 3: xz
441- Cypher used for the event packet content. Applied after compression.
5ba9f198
MD
442 0: no encryption
443 1: AES
3bf79539 444- Checksum scheme used for the event packet content. Applied after encryption.
5ba9f198
MD
445 0: no checksum
446 1: md5
447 2: sha1
448 3: crc32
449
3bf79539
MD
4505.1 Event Packet Header Fixed Layout Description
451
80fd2569
MD
452struct event_packet_header {
453 uint32_t magic;
454 uint8_t trace_uuid[16];
3bf79539 455 uint32_t stream_id;
80fd2569 456};
5ba9f198 457
3bf79539
MD
4585.2 Event Packet Context Description
459
460Event packet context example. These are declared within the stream declaration
461in the metadata. All these fields are optional except for "content_size" and
462"packet_size", which must be present in the context.
463
464An example event packet context type:
465
80fd2569 466struct event_packet_context {
3bf79539
MD
467 uint64_t timestamp_begin;
468 uint64_t timestamp_end;
469 uint32_t checksum;
470 uint32_t stream_packet_count;
471 uint32_t events_discarded;
472 uint32_t cpu_id;
473 uint32_t/uint16_t content_size;
474 uint32_t/uint16_t packet_size;
475 uint8_t stream_packet_count_bits; /* Significant counter bits */
476 uint8_t compression_scheme;
477 uint8_t encryption_scheme;
478 uint8_t checksum;
479};
5ba9f198
MD
480
4816. Event Structure
482
483The overall structure of an event is:
484
3bf79539 485 - Event Header (as specifed by the stream metadata)
5ba9f198 486 - Extended Event Header (as specified by the event header)
3bf79539 487 - Event Context (as specified by the stream metadata)
5ba9f198
MD
488 - Event Payload (as specified by the event metadata)
489
490
4916.1 Event Header
492
3bf79539
MD
493One major factor can vary between streams: the number of event IDs assigned to
494a stream. Luckily, this information tends to stay relatively constant (modulo
5ba9f198 495event registration while trace is being recorded), so we can specify different
3bf79539 496representations for streams containing few event IDs and streams containing
5ba9f198
MD
497many event IDs, so we end up representing the event ID and timestamp as densely
498as possible in each case.
499
3bf79539
MD
500We therefore provide two types of events headers. Type 1 accommodates streams
501with less than 31 event IDs. Type 2 accommodates streams with 31 or more event
5ba9f198
MD
502IDs.
503
504The "extended headers" are used in the rare occasions where the information
3bf79539
MD
505cannot be represented in the ranges available in the event header. They are also
506used in the rare occasions where the data required for a field could not be
507collected: the flag corresponding to the missing field within the missing_fields
508array is then set to 1.
5ba9f198
MD
509
510Types uintX_t represent an X-bit unsigned integer.
511
512
5136.1.1 Type 1 - Few event IDs
514
515 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
516 preference).
517 - Fixed size: 32 bits.
518 - Native architecture byte ordering.
519
80fd2569
MD
520struct event_header_1 {
521 uint5_t id; /*
5ba9f198
MD
522 * id: range: 0 - 30.
523 * id 31 is reserved to indicate a following
524 * extended header.
525 */
80fd2569 526 uint27_t timestamp;
5ba9f198
MD
527};
528
529The end of a type 1 header is aligned on a 32-bit boundary (or packed).
530
531
5326.1.2 Extended Type 1 Event Header
533
534 - Follows struct event_header_1, which is aligned on 32-bit, so no need to
535 realign.
3bf79539 536 - Variable size (depends on the number of fields per event).
5ba9f198 537 - Native architecture byte ordering.
80fd2569 538 - NR_FIELDS is the number of fields within the event.
5ba9f198 539
80fd2569
MD
540struct event_header_1_ext {
541 uint32_t id; /* 32-bit event IDs */
542 uint64_t timestamp; /* 64-bit timestamps */
543 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
5ba9f198
MD
544};
545
5ba9f198
MD
546
5476.1.3 Type 2 - Many event IDs
548
549 - Aligned on 32-bit (or 8-bit if byte-packed, depending on the architecture
550 preference).
551 - Fixed size: 48 bits.
552 - Native architecture byte ordering.
553
80fd2569
MD
554struct event_header_2 {
555 uint32_t timestamp;
556 uint16_t id; /*
5ba9f198
MD
557 * id: range: 0 - 65534.
558 * id 65535 is reserved to indicate a following
559 * extended header.
560 */
5ba9f198
MD
561};
562
563The end of a type 2 header is aligned on a 16-bit boundary (or 8-bit if
564byte-packed).
565
566
5676.1.4 Extended Type 2 Event Header
568
569 - Follows struct event_header_2, which alignment end on a 16-bit boundary, so
3bf79539 570 we need to align on 64-bit integer architecture alignment (or 8-bit if
5ba9f198 571 byte-packed).
3bf79539 572 - Variable size (depends on the number of fields per event).
5ba9f198 573 - Native architecture byte ordering.
80fd2569 574 - NR_FIELDS is the number of fields within the event.
5ba9f198 575
80fd2569
MD
576struct event_header_2_ext {
577 uint64_t timestamp; /* 64-bit timestamps */
578 uint32_t id; /* 32-bit event IDs */
579 uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
5ba9f198
MD
580};
581
5ba9f198
MD
582
5836.2 Event Context
584
585The event context contains information relative to the current event. The choice
3bf79539 586and meaning of this information is specified by the metadata "stream"
5ba9f198 587information. For this trace format, event context is usually empty, except when
3bf79539 588the metadata "stream" information specifies otherwise by declaring a non-empty
5ba9f198
MD
589structure for the event context. An example of event context is to save the
590event payload size with each event, or to save the current PID with each event.
3bf79539 591These are declared within the stream declaration within the metadata.
5ba9f198 592
3bf79539 593An example event context type:
5ba9f198 594
80fd2569
MD
595 struct event_context {
596 uint pid;
597 uint16_t payload_size;
3bf79539 598 };
5ba9f198
MD
599
600
6016.3 Event Payload
602
603An event payload contains fields specific to a given event type. The fields
604belonging to an event type are described in the event-specific metadata
605within a structure type.
606
6076.3.1 Padding
608
609No padding at the end of the event payload. This differs from the ISO/C standard
610for structures, but follows the CTF standard for structures. In a trace, even
611though it makes sense to align the beginning of a structure, it really makes no
612sense to add padding at the end of the structure, because structures are usually
613not followed by a structure of the same type.
614
615This trick can be done by adding a zero-length "end" field at the end of the C
616structures, and by using the offset of this field rather than using sizeof()
3bf79539 617when calculating the size of a structure (see Appendix "A. Helper macros").
5ba9f198
MD
618
6196.3.2 Alignment
620
621The event payload is aligned on the largest alignment required by types
622contained within the payload. (This follows the ISO/C standard for structures)
623
624
625
6267. Metadata
627
3bf79539
MD
628The meta-data is located in a stream named "metadata". It is made of "event
629packets", which each start with an event packet header. The event type within
630the metadata stream have no event header nor event context. Each event only
5ba9f198 631contains a null-terminated "string" payload, which is a metadata description
3bf79539
MD
632entry. The events are packed one next to another. Each event packet start with
633an event packet header, which contains, amongst other fields, the magic number
634and trace UUID.
5ba9f198
MD
635
636The metadata can be parsed by reading through the metadata strings, skipping
3bf79539 637newlines and null-characters. Type names may contain spaces.
5ba9f198
MD
638
639trace {
640 major = value; /* Trace format version */
641 minor = value;
3bf79539
MD
642 uuid = value; /* Trace UUID */
643 word_size = value;
644};
5ba9f198 645
3bf79539
MD
646stream {
647 id = stream_id;
5ba9f198 648 event {
3bf79539
MD
649 /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
650 header_type = event_header_1 OR event_header_2;
651 /*
652 * Extended event header type. Only present if specified in event header
653 * on a per-event basis.
654 */
655 header_type_ext = event_header_1_ext OR event_header_2_ext;
80fd2569
MD
656 context_type = struct {
657 ...
658 };
3bf79539
MD
659 };
660 packet {
80fd2569
MD
661 context_type = struct {
662 ...
663 };
3bf79539
MD
664 };
665};
5ba9f198
MD
666
667event {
3d13ef1a 668 name = event_name;
3bf79539
MD
669 id = value; /* Numeric identifier within the stream */
670 stream = stream_id;
80fd2569
MD
671 fields = struct {
672 ...
673 };
3bf79539 674};
5ba9f198
MD
675
676/* More detail on types in section 4. Types */
677
3d13ef1a
MD
678/*
679 * Named types:
680 *
681 * A named type can only have a prefix and postfix if it aliases a CTF basic
682 * type. A type name aliasing another type name cannot have prefix nor postfix,
683 * but the type aliased can have a prefix and/or postfix.
684 */
685
686typedef aliased_type_prefix aliased_type new_type aliased_type_postfix;
2152348f 687
3d13ef1a 688/* e.g.: typedef struct example new_type_name[10]; */
80fd2569
MD
689
690typedef type_class {
691 ...
3d13ef1a 692} new_type_prefix new_type new_type_postfix;
2152348f 693
3d13ef1a
MD
694/*
695 * e.g.:
696 * typedef integer {
697 * size = 32;
698 * align = 32;
699 * signed = false;
700 * } struct page *;
701 */
80fd2569
MD
702
703struct name {
3bf79539
MD
704 ...
705};
5ba9f198 706
4767a9e7 707enum <integer_type or size> name {
3bf79539
MD
708 ...
709};
710
2152348f
MD
711
712/* Unnamed types, contained within compound type fields or typedef. */
713
80fd2569
MD
714struct {
715 ...
2152348f 716}
5ba9f198 717
4767a9e7 718enum <integer_type or size> {
80fd2569 719 ...
2152348f
MD
720}
721
722typedef type new_type[length];
3bf79539 723
2152348f
MD
724struct {
725 type field_name[length];
726}
727
728typedef type new_type[length_type];
729
730struct {
731 type field_name[length_type];
732}
733
734integer {
80fd2569 735 ...
2152348f 736}
3bf79539 737
2152348f 738floating_point {
80fd2569 739 ...
2152348f
MD
740}
741
742struct {
743 integer_type field_name:size; /* GNU/C bitfield */
744}
745
746struct {
747 string field_name;
748}
3bf79539
MD
749
750A. Helper macros
5ba9f198
MD
751
752The two following macros keep track of the size of a GNU/C structure without
753padding at the end by placing HEADER_END as the last field. A one byte end field
754is used for C90 compatibility (C99 flexible arrays could be used here). Note
755that this does not affect the effective structure size, which should always be
756calculated with the header_sizeof() helper.
757
758#define HEADER_END char end_field
759#define header_sizeof(type) offsetof(typeof(type), end_field)
3bf79539
MD
760
761
762B. Stream Header Rationale
763
764An event stream is divided in contiguous event packets of variable size. These
765subdivisions allow the trace analyzer to perform a fast binary search by time
766within the stream (typically requiring to index only the event packet headers)
767without reading the whole stream. These subdivisions have a variable size to
768eliminate the need to transfer the event packet padding when partially filled
769event packets must be sent when streaming a trace for live viewing/analysis.
770An event packet can contain a certain amount of padding at the end. Dividing
771streams into event packets is also useful for network streaming over UDP and
772flight recorder mode tracing (a whole event packet can be swapped out of the
773buffer atomically for reading).
774
775The stream header is repeated at the beginning of each event packet to allow
776flexibility in terms of:
777
778 - streaming support,
779 - allowing arbitrary buffers to be discarded without making the trace
780 unreadable,
781 - allow UDP packet loss handling by either dealing with missing event packet
782 or asking for re-transmission.
783 - transparently support flight recorder mode,
784 - transparently support crash dump.
785
786The event stream header will therefore be referred to as the "event packet
787header" throughout the rest of this document.
This page took 0.093168 seconds and 4 git commands to generate.