-RFC: Common Trace Format Proposal for Linux (v1)
+RFC: Common Trace Format Proposal for Linux (v1.6)
Mathieu Desnoyers, EfficiOS Inc.
The goal of the present document is to propose a trace format that suits the
needs of the embedded, telecom, high-performance and kernel communities. It is
based on the Common Trace Format Requirements (v1.4) document. It is designed to
-be natively generated by tracing of a Linux kernel and Linux user-space
-applications written in C/C++.
+allow tracing that is natively generated by the Linux kernel and Linux
+user-space applications written in C/C++.
A reference implementation of a library to read and write this trace format is
being implemented within the BabelTrace project, a converter between trace
1. Preliminary definitions
- - Trace: An ordered sequence of events.
- - Section: Group of events, containing a subset of the trace event types.
- - Packet: A sequence of physically contiguous events within a section.
+ - Event Trace: An ordered sequence of events.
+ - Event Stream: An ordered sequence of events, containing a subset of the
+ trace event types.
+ - Event Packet: A sequence of physically contiguous events within an event
+ stream.
- Event: This is the basic entry in a trace. (aka: a trace record).
- An event identifier (ID) relates to the class (a type) of event within
- a section.
- e.g. section: high_throughput, event: irq_entry.
+ an event stream.
+ e.g. event: irq_entry.
- An event (or event record) relates to a specific instance of an event
class.
- e.g. section: high_throughput, event: irq_entry, at time X, on CPU Y
+ e.g. event: irq_entry, at time X, on CPU Y
+ - Source Architecture: Architecture writing the trace.
+ - Reader Architecture: Architecture reading the trace.
2. High-level representation of a trace
-A trace is divided into multiple trace streams, each representing an information
-stream specific to:
+A trace is divided into multiple event streams. Each event stream contains a
+subset of the trace event types.
- - a section,
- - a processor.
+The final output of the trace, after its generation and optional transport over
+the network, is expected to be either on permanent or temporary storage in a
+virtual file system. Because each event stream is appended to while a trace is
+being recorded, each is associated with a separate file for output. Therefore,
+a stored trace can be represented as a directory containing one file per stream.
-A trace "section" consists of a collection of trace streams (typically one trace
-stream per cpu) containing a subset of the trace event types.
-
-Because each trace stream is appended to while a trace is being recorded, each
-is associated with a separate file for disk output. Therefore, a trace stored to
-disk can be represented as a directory containing one file per section.
-
-A metadata section contains information on trace event types. It describes:
+A metadata event stream contains information on trace event types. It describes:
- Trace version.
- Types available.
-- Per-section event header description.
-- Per-section event header selection.
-- Per-section event context fields.
+- Per-stream event header description.
+- Per-stream event header selection.
+- Per-stream event context fields.
- Per-event
- - Event type to section mapping.
+ - Event type to stream mapping.
- Event type to name mapping.
- Event type to ID mapping.
- Event fields description.
-3. Trace Section
+3. Event stream
-A trace section is divided in contiguous packets of variable size. These
-subdivisions allow the trace analyzer to perform a fast binary search by time
-within the section (typically requiring to index only the packet headers)
-without reading the whole section. These subdivisions have a variable size to
-eliminate the need to transfer the packet padding when partially filled packets
-must be sent when streaming a trace for live viewing/analysis. Dividing sections
-into packets is also useful for network streaming over UDP and flight recorder
-mode tracing (a whole packet can be swapped out of the buffer atomically for
-reading).
-
-The section header is repeated at the beginning of each packet to allow
-flexibility in terms of:
+An event stream is divided in contiguous event packets of variable size. These
+subdivisions have a variable size. An event packet can contain a certain amount
+of padding at the end. The rationale for the event stream design choices is
+explained in Appendix B. Stream Header Rationale.
- - streaming support,
- - allowing arbitrary buffers to be discarded without making the trace
- unreadable,
- - allow UDP packet loss handling by either dealing with missing packet or
- asking for re-transmission.
- - transparently support flight recorder mode,
- - transparently support crash dump.
+An event stream is divided in contiguous event packets of variable size. These
+subdivisions have a variable size. An event packet can contain a certain amount
+of padding at the end. The stream header is repeated at the beginning of each
+event packet.
-The section header will therefore be referred to as the "packet header"
-thorough the rest of this document.
+The event stream header will therefore be referred to as the "event packet
+header" throughout the rest of this document.
4. Types
4.1.1 Type inheritance
-Type specifications can be inherited to allow deriving concrete types from an
-abstract type. For example, see the uint32_t type derived from the "integer"
-abstract type below ("Integers" section). Concrete types have a precise binary
-representation in the trace. Abstract types have methods to read and write these
-types, but must be derived into a concrete type to be usable in an event field.
-
-Concrete types inherit from abstract types. Abstract types can inherit from
-other abstract types.
+Type specifications can be inherited to allow deriving types from a
+type class. For example, see the uint32_t named type derived from the "integer"
+type class below ("Integers" section). Types have a precise binary
+representation in the trace. A type class has methods to read and write these
+types, but must be derived into a type to be usable in an event field.
4.1.2 Alignment
We define "byte-packed" types as aligned on the byte size, namely 8-bit.
We define "bit-packed" types as following on the next bit, as defined by the
"bitfields" section.
-We define "natural alignment" of a basic type as the lesser value between the
-type size and the architecture word size.
-All basic types, except bitfields, are either aligned on their "natural"
-alignment or byte-packed, depending on the architecture preference.
-Architectures providing fast unaligned writes byte-packed basic types to save
+All basic types, except bitfields, are either aligned on an architecture-defined
+specific alignment or byte-packed, depending on the architecture preference.
+Architectures providing fast unaligned write byte-packed basic types to save
space, aligning each type on byte boundaries (8-bit). Architectures with slow
-unaligned writes align types on the lesser value between their size and the
-architecture word size (the type "natural" alignment on the architecture).
+unaligned writes align types on specific alignment values. If no specific
+alignment is declared for a type nor its parents, it is assumed to be bit-packed
+for bitfields and byte-packed for other types.
-Note that the natural alignment for 64-bit integers and double-precision
-floating point values is fixed to 32-bit on a 32-bit architecture, but to 64-bit
-for a 64-bit architecture.
-
-Metadata attribute representation:
+Metadata attribute representation of a specific alignment:
align = value; /* value in bits */
4.1.3 Byte order
-By default, target architecture endianness is used. Byte order can be overridden
-for a basic type by specifying a "byte_order" attribute. Typical use-case is to
-specify the network byte order (big endian: "be") to save data captured from the
-network into the trace without conversion. If not specified, the byte order is
-native.
+By default, the native endianness of the source architecture the trace is used.
+Byte order can be overridden for a basic type by specifying a "byte_order"
+attribute. Typical use-case is to specify the network byte order (big endian:
+"be") to save data captured from the network into the trace without conversion.
+If not specified, the byte order is native.
Metadata representation:
Metadata representation:
- abstract_type integer {
+ integer {
signed = true OR false; /* default false */
byte_order = native OR network OR be OR le; /* default native */
size = value; /* value in bits, no default */
align = value; /* value in bits */
- }
+ };
-Example of type inheritance (creation of a concrete type uint32_t):
+Example of type inheritance (creation of a uint32_t named type):
-type uint32_t {
- parent = integer;
- size = 8;
+typedef integer {
+ size = 32;
signed = false;
align = 32;
-}
+} uint32_t;
-Definition of a 5-bit signed bitfield:
+Definition of a named 5-bit signed bitfield:
-type int5_t {
- parent = integer;
+typedef integer {
size = 5;
signed = true;
align = 1;
-}
+} int5_t;
4.1.6 GNU/C bitfields
The GNU/C bitfields follow closely the integer representation, with a
particularity on alignment: if a bitfield cannot fit in the current unit, the
-unit is padded and the bitfield starts at the following unit. We therefore need
-to express the extra "unit size" information.
+unit is padded and the bitfield starts at the following unit. The unit size is
+defined by the size of the type "unit_type".
-Metadata representation:
+Metadata representation. Either:
-abstract_type gcc_bitfield {
- parent = integer;
- unit_size = value;
-}
+gcc_bitfield {
+ unit_type = integer {
+ ...
+ };
+ size = value;
+};
+
+Or bitfield within structures as specified by the C standard
+
+ unit_type name:size:
As an example, the following structure declared in C compiled by GCC:
short b:5;
};
-Would correspond to the following structure, aligned on the largest element
-(short). The second bitfield would be aligned on the next unit boundary, because
-it would not fit in the current unit.
-
-type struct_example {
- parent = struct;
- fields = {
- {
- type {
- parent = gcc_bitfield;
- unit_size = 16; /* sizeof(short) */
- size = 12;
- signed = true;
- align = 1;
- },
- a,
- },
- {
- type {
- parent = gcc_bitfield;
- unit_size = 16; /* sizeof(short) */
- size = 5;
- signed = true;
- align = 1;
- },
- b,
- },
- };
-}
+is equivalent to the following structure declaration, aligned on the largest
+element (short). The second bitfield would be aligned on the next unit boundary,
+because it would not fit in the current unit. The two declarations (C
+declaration above or CTF declaration with "type gcc_bitfield") are strictly
+equivalent.
+
+struct example {
+ gcc_bitfield {
+ unit_type = short;
+ size = 12;
+ } a;
+ gcc_bitfield {
+ unit_type = short;
+ size = 5;
+ } b;
+};
4.1.7 Floating point
Metadata representation:
-abstract_type floating_point {
+floating_point {
exp_dig = value;
mant_dig = value;
byte_order = native OR network OR be OR le;
-}
+};
Example of type inheritance:
-type float {
+typedef floating_point {
exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
mant_dig = 24; /* FLT_MANT_DIG */
byte_order = native;
-}
+} float;
TODO: define NaN, +inf, -inf behavior.
Enumerations are a mapping between an integer type and a table of strings. The
numerical representation of the enumeration follows the integer type specified
by the metadata. The enumeration mapping table is detailed in the enumeration
-description within the metadata.
-
-abstract_type enum {
- .parent = integer;
- .map = {
- { value , string },
- { value , string },
- { value , string },
- ...
- };
-}
+description within the metadata. The mapping table maps inclusive value ranges
+(or single values) to strings. Instead of being limited to simple
+"value -> string" mappings, these enumerations map
+"[ start_value ... end_value ] -> string", which map inclusive ranges of
+values to strings. An enumeration from the C language can be represented in
+this format by having the same start_value and end_value for each element, which
+is in fact a range of size 1. This single-value range is supported without
+repeating the start and end values with the value = string declaration. If the
+<integer_type> is omitted, the type chosen by the C compiler to hold the
+enumeration is used. The <integer_type> specifier can only be omitted for
+enumerations containing only simple "value -> string" mappings (compatible with
+C).
+
+enum <integer_type> name {
+ string = start_value1 ... end_value1,
+ "other string" = start_value2 ... end_value2,
+ yet_another_string, /* will be assigned to end_value2 + 1 */
+ "some other string" = value,
+ ...
+};
+If the values are omitted, the enumeration starts at 0 and increment of 1 for
+each entry:
+
+enum {
+ ZERO,
+ ONE,
+ TWO,
+ TEN = 10,
+ ELEVEN,
+};
+
+Overlapping ranges within a single enumeration are implementation defined.
4.2 Compound types
Structures are aligned on the largest alignment required by basic types
contained within the structure. (This follows the ISO/C standard for structures)
-Metadata representation:
+Metadata representation of a named structure:
-abstract_type struct {
- fields = {
- { field_type, field_name },
- { field_type, field_name },
- ...
- };
-}
+struct name {
+ field_type field_name;
+ field_type field_name;
+ ...
+};
Example:
-type struct_example {
- parent = struct;
- fields = {
- {
- type { /* Nameless type */
- parent = integer;
- size = 16;
- signed = true;
- align = 16;
- },
- first_field_name,
- },
- {
- uint64_t, /* Named type declared in the metadata */
- second_field_name,
- }
- };
-}
+struct example {
+ integer { /* Nameless type */
+ size = 16;
+ signed = true;
+ align = 16;
+ } first_field_name;
+ uint64_t second_field_name; /* Named type declared in the metadata */
+};
The fields are placed in a sequence next to each other. They each possess a
field name, which is a unique identifier within the structure.
+A nameless structure can be declared as a field type:
+
+struct {
+ ...
+} field_name;
+
4.2.2 Arrays
Arrays are fixed-length. Their length is declared in the type declaration within
the metadata. They contain an array of "inner type" elements, which can refer to
any type not containing the type of the array being declared (no circular
-dependency).
+dependency). The length is the number of elements in an array.
-Metadata representation:
+Metadata representation of a named array, either:
-abstract_type array {
+typedef array {
length = value;
elem_type = type;
-}
+} name;
+
+or:
+
+typedef elem_type name[length];
E.g.:
-type example_array {
- parent = array;
+typedef array {
length = 10;
elem_type = uint32_t;
-}
+} example;
+
+A nameless array can be declared as a field type, e.g.:
+
+array {
+ length = 5;
+ elem_type = uint8_t;
+} field_name;
+
+or
+
+uint8_t field_name[10];
+
4.2.3 Sequences
Sequences are dynamically-sized arrays. They start with an integer that specify
the length of the sequence, followed by an array of "inner type" elements.
+The length is the number of elements in the sequence.
-abstract_type sequence {
- length_type = type; /* Inheriting from integer */
+Metadata representation for a named sequence, either:
+
+typedef sequence {
+ length_type = type; /* integer class */
elem_type = type;
-}
+} name;
+
+or:
+
+typedef elem_type name[length_type];
+
+A nameless sequence can be declared as a field type, e.g.:
+
+sequence {
+ length_type = int;
+ elem_type = long;
+} field_name;
+
+or
-The integer type follows the integer types specifications, and the sequence
+long field_name[int];
+
+The length type follows the integer types specifications, and the sequence
elements follow the "array" specifications.
4.2.4 Strings
"NULL" character. Their encoding is described in the metadata. In absence of
encoding attribute information, the default encoding is UTF-8.
-abstract_type string {
+Metadata representation of a named string type:
+
+typedef string {
encoding = UTF8 OR ASCII;
-}
+} name;
+A nameless string type can be declared as a field type:
-5. Trace Packet Header
+string field_name; /* Use default UTF8 encoding */
-- Aligned on page size. Fixed size. Fields aligned on their natural size or
- packed (depending on the architecture preference).
- No padding at the end of the trace packet header. Native architecture byte
+5. Event Packet Header
+
+The event packet header consists of two part: one is mandatory and have a fixed
+layout. The second part, the "event packet context", has its layout described in
+the metadata.
+
+- Aligned on page size. Fixed size. Fields either aligned or packed (depending
+ on the architecture preference).
+ No padding at the end of the event packet header. Native architecture byte
ordering.
+
+Fixed layout (event packet header):
+
- Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness
representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise
representation. Used to distinguish between big and little endian traces (this
reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata
description language described in this document. Different magic numbers
should be used for other metadata description languages.
-- Session ID, used to ensure the packet match the metadata used.
+- Trace UUID, used to ensure the event packet match the metadata used.
(note: we cannot use a metadata checksum because metadata can be appended to
while tracing is active)
-- Packet content size (in bytes).
-- Packet size (in bytes, includes padding).
-- Packet content checksum (optional). Checksum excludes the packet header.
-- Per-section packet sequence count (to deal with UDP packet loss). The number
- of significant sequence counter bits should also be present, so wrap-arounds
- are deal with correctly.
-- Timestamp at the beginning and end of the packet. Should include all
- event timestamps contained therein.
+- Stream ID, used as reference to stream description in metadata.
+
+Metadata-defined layout (event packet context):
+
+- Event packet content size (in bytes).
+- Event packet size (in bytes, includes padding).
+- Event packet content checksum (optional). Checksum excludes the event packet
+ header.
+- Per-stream event packet sequence count (to deal with UDP packet loss). The
+ number of significant sequence counter bits should also be present, so
+ wrap-arounds are deal with correctly.
+- Timestamp at the beginning and timestamp at the end of the event packet.
+ Both timestamps are written in the packet header, but sampled respectively
+ while (or before) writing the first event and while (or after) writing the
+ last event in the packet. The inclusive range between these timestamps should
+ include all event timestamps assigned to events contained within the packet.
- Events discarded count
- - Snapshot of a per-section free-running counter, counting the number of
- events discarded that were supposed to be written in the section prior to
- the first event in the packet.
+ - Snapshot of a per-stream free-running counter, counting the number of
+ events discarded that were supposed to be written in the stream prior to
+ the first event in the event packet.
* Note: producer-consumer buffer full condition should fill the current
- packet with padding so we know exactly where events have been
+ event packet with padding so we know exactly where events have been
discarded.
-- Lossless compression scheme used for the packet content. Applied directly to
- raw data.
+- Lossless compression scheme used for the event packet content. Applied
+ directly to raw data. New types of compression can be added in following
+ versions of the format.
0: no compression scheme
1: bzip2
2: gzip
-- Cypher used for the packet content. Applied after compression.
+ 3: xz
+- Cypher used for the event packet content. Applied after compression.
0: no encryption
1: AES
-- Checksum scheme used for the packet content. Applied after encryption.
+- Checksum scheme used for the event packet content. Applied after encryption.
0: no checksum
1: md5
2: sha1
3: crc32
-type packet_header {
- parent = struct;
- fields = {
- { uint32_t, magic },
- { uint32_t, session_id },
- { uint32_t, content_size },
- { uint32_t, packet_size },
- { uint32_t, checksum },
- { uint32_t, section_packet_count },
- { uint64_t, timestamp_begin }
- { uint64_t, timestamp_end }
- [ uint32_t, events_discarded },
- { uint8_t, section_packet_count_bits }, /* Significant counter bits */
- { uint8_t, compression_scheme },
- { uint8_t, encryption_scheme },
- { uint8_t, checksum },
- };
+5.1 Event Packet Header Fixed Layout Description
+
+struct event_packet_header {
+ uint32_t magic;
+ uint8_t trace_uuid[16];
+ uint32_t stream_id;
};
+5.2 Event Packet Context Description
+
+Event packet context example. These are declared within the stream declaration
+in the metadata. All these fields are optional except for "content_size" and
+"packet_size", which must be present in the context.
+
+An example event packet context type:
+
+struct event_packet_context {
+ uint64_t timestamp_begin;
+ uint64_t timestamp_end;
+ uint32_t checksum;
+ uint32_t stream_packet_count;
+ uint32_t events_discarded;
+ uint32_t cpu_id;
+ uint32_t/uint16_t content_size;
+ uint32_t/uint16_t packet_size;
+ uint8_t stream_packet_count_bits; /* Significant counter bits */
+ uint8_t compression_scheme;
+ uint8_t encryption_scheme;
+ uint8_t checksum;
+};
6. Event Structure
The overall structure of an event is:
- - Event Header (as specifed by the section metadata)
+ - Event Header (as specifed by the stream metadata)
- Extended Event Header (as specified by the event header)
- - Event Context (as specified by the section metadata)
+ - Event Context (as specified by the stream metadata)
- Event Payload (as specified by the event metadata)
6.1 Event Header
-One major factor can vary between sections: the number of event IDs assigned to
-a section. Luckily, this information tends to stay relatively constant (modulo
+One major factor can vary between streams: the number of event IDs assigned to
+a stream. Luckily, this information tends to stay relatively constant (modulo
event registration while trace is being recorded), so we can specify different
-representations for sections containing few event IDs and sections containing
+representations for streams containing few event IDs and streams containing
many event IDs, so we end up representing the event ID and timestamp as densely
as possible in each case.
-We therefore provide two types of events headers. Type 1 accommodates sections
-with less than 31 event IDs. Type 2 accommodates sections with 31 or more event
+We therefore provide two types of events headers. Type 1 accommodates streams
+with less than 31 event IDs. Type 2 accommodates streams with 31 or more event
IDs.
The "extended headers" are used in the rare occasions where the information
-cannot be represented in the ranges available in the event header.
+cannot be represented in the ranges available in the event header. They are also
+used in the rare occasions where the data required for a field could not be
+collected: the flag corresponding to the missing field within the missing_fields
+array is then set to 1.
Types uintX_t represent an X-bit unsigned integer.
- Fixed size: 32 bits.
- Native architecture byte ordering.
-type event_header_1 {
- parent = struct;
- fields = {
- { uint5_t, id }, /*
+struct event_header_1 {
+ uint5_t id; /*
* id: range: 0 - 30.
* id 31 is reserved to indicate a following
* extended header.
*/
- { uint27_t, timestamp },
- };
+ uint27_t timestamp;
};
The end of a type 1 header is aligned on a 32-bit boundary (or packed).
- Follows struct event_header_1, which is aligned on 32-bit, so no need to
realign.
- - Fixed size: 96 bits.
+ - Variable size (depends on the number of fields per event).
- Native architecture byte ordering.
+ - NR_FIELDS is the number of fields within the event.
-type event_header_1_ext {
- parent = struct;
- fields = {
- { uint32_t, id }, /* 32-bit event IDs */
- { uint64_t, timestamp }, /* 64-bit timestamps */
- };
+struct event_header_1_ext {
+ uint32_t id; /* 32-bit event IDs */
+ uint64_t timestamp; /* 64-bit timestamps */
+ uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
};
-The end of a type 1 extended header is aligned on the natural alignment of a
-64-bit integer (or 8-bit if byte-packed).
-
6.1.3 Type 2 - Many event IDs
- Fixed size: 48 bits.
- Native architecture byte ordering.
-type event_header_2 {
- parent = struct;
- fields = {
- { uint32_t, timestamp },
- { uint16_t, id }, /*
+struct event_header_2 {
+ uint32_t timestamp;
+ uint16_t id; /*
* id: range: 0 - 65534.
* id 65535 is reserved to indicate a following
* extended header.
*/
- };
};
The end of a type 2 header is aligned on a 16-bit boundary (or 8-bit if
6.1.4 Extended Type 2 Event Header
- Follows struct event_header_2, which alignment end on a 16-bit boundary, so
- we need to align on 64-bit integer natural alignment (or 8-bit if
+ we need to align on 64-bit integer architecture alignment (or 8-bit if
byte-packed).
- - Fixed size: 96 bits.
+ - Variable size (depends on the number of fields per event).
- Native architecture byte ordering.
+ - NR_FIELDS is the number of fields within the event.
-type event_header_2_ext {
- parent = struct;
- fields = {
- { uint64_t, timestamp }, /* 64-bit timestamps */
- { uint32_t, id }, /* 32-bit event IDs */
- };
+struct event_header_2_ext {
+ uint64_t timestamp; /* 64-bit timestamps */
+ uint32_t id; /* 32-bit event IDs */
+ uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */
};
-The end of a type 2 extended header is aligned on the natural alignment of a
-32-bit integer (or 8-bit if byte-packed).
-
6.2 Event Context
The event context contains information relative to the current event. The choice
-and meaning of this information is specified by the metadata "section"
+and meaning of this information is specified by the metadata "stream"
information. For this trace format, event context is usually empty, except when
-the metadata "section" information specifies otherwise by declaring a non-empty
+the metadata "stream" information specifies otherwise by declaring a non-empty
structure for the event context. An example of event context is to save the
event payload size with each event, or to save the current PID with each event.
+These are declared within the stream declaration within the metadata.
-6.2.1 Event Context Description
+An example event context type:
-Event context example. These are declared within the section declaration within
-the metadata.
-
-type per_section_event_ctx {
- parent = struct;
- fields = {
- { uint, pid },
- { uint16_t, payload_size },
- };
-};
+ struct event_context {
+ uint pid;
+ uint16_t payload_size;
+ };
6.3 Event Payload
This trick can be done by adding a zero-length "end" field at the end of the C
structures, and by using the offset of this field rather than using sizeof()
-when calculating the size of a structure (see section "A.1 Helper macros").
+when calculating the size of a structure (see Appendix "A. Helper macros").
6.3.2 Alignment
7. Metadata
-The meta-data is located in a tracefile section named "metadata". It is made of
-"packets", which each start with a packet header. The event type within the
-metadata section have no event header nor event context. Each event only
+The meta-data is located in a stream named "metadata". It is made of "event
+packets", which each start with an event packet header. The event type within
+the metadata stream have no event header nor event context. Each event only
contains a null-terminated "string" payload, which is a metadata description
-entry. The events are packed one next to another. Each packet start with a
-packet header, which contains, amongst other fields, the session ID and magic
-number.
+entry. The events are packed one next to another. Each event packet start with
+an event packet header, which contains, amongst other fields, the magic number
+and trace UUID.
The metadata can be parsed by reading through the metadata strings, skipping
-spaces, newlines and null-characters.
+newlines and null-characters. Type names may contain spaces.
trace {
major = value; /* Trace format version */
minor = value;
-}
+ uuid = value; /* Trace UUID */
+ word_size = value;
+};
-section {
- name = section_name;
+stream {
+ id = stream_id;
event {
- /* Type 1 - Few event IDs; Type 2 - Many event IDs */
- header_type = type1 OR type2;
- context {
- event_size = true OR false; /* Includes event size field or not */
- }
- }
-}
+ /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
+ header_type = event_header_1 OR event_header_2;
+ /*
+ * Extended event header type. Only present if specified in event header
+ * on a per-event basis.
+ */
+ header_type_ext = event_header_1_ext OR event_header_2_ext;
+ context_type = struct {
+ ...
+ };
+ };
+ packet {
+ context_type = struct {
+ ...
+ };
+ };
+};
event {
- name = event_name;
- id = value; /* Numeric identifier within the section */
- section = section_name;
- fields = type inheriting from "struct" abstract type.
-}
+ name = eventname;
+ id = value; /* Numeric identifier within the stream */
+ stream = stream_id;
+ fields = struct {
+ ...
+ };
+};
/* More detail on types in section 4. Types */
/* Named types */
-type typename {
- ...
-}
+typedef some existing type new_type;
+
+typedef type_class {
+ ...
+} new_type;
+
+struct name {
+ ...
+};
-/* Unnamed types, contained within compound type fields */
-type {
- ...
-}
+enum name {
+ ...
+};
+
+/* Unnamed types, contained within compound type fields or type assignments. */
+struct {
+ ...
+};
+
+enum {
+ ...
+};
+
+array {
+ ...
+};
+
+sequence {
+ ...
+};
-A.1 Helper macros
+A. Helper macros
The two following macros keep track of the size of a GNU/C structure without
padding at the end by placing HEADER_END as the last field. A one byte end field
#define HEADER_END char end_field
#define header_sizeof(type) offsetof(typeof(type), end_field)
+
+
+B. Stream Header Rationale
+
+An event stream is divided in contiguous event packets of variable size. These
+subdivisions allow the trace analyzer to perform a fast binary search by time
+within the stream (typically requiring to index only the event packet headers)
+without reading the whole stream. These subdivisions have a variable size to
+eliminate the need to transfer the event packet padding when partially filled
+event packets must be sent when streaming a trace for live viewing/analysis.
+An event packet can contain a certain amount of padding at the end. Dividing
+streams into event packets is also useful for network streaming over UDP and
+flight recorder mode tracing (a whole event packet can be swapped out of the
+buffer atomically for reading).
+
+The stream header is repeated at the beginning of each event packet to allow
+flexibility in terms of:
+
+ - streaming support,
+ - allowing arbitrary buffers to be discarded without making the trace
+ unreadable,
+ - allow UDP packet loss handling by either dealing with missing event packet
+ or asking for re-transmission.
+ - transparently support flight recorder mode,
+ - transparently support crash dump.
+
+The event stream header will therefore be referred to as the "event packet
+header" throughout the rest of this document.
projects / ctf.git / blobdiff