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Microsoft.LinuxTracepoints.Decode

.NET library for parsing perf.data files and decoding tracepoint events. This includes decoding of perf.data files, parsing of tracefs format files, formatting of tracepoint event fields, and decoding of tracepoints that use the EventHeader decoding system.

Decoding procedure

For an example, see DecodeSample.

  • Create a file reader: var reader = new PerfDataFileReader().

  • If you will be decoding events that use the EventHeader decoding system, create an enumerator to use for decoding them: var eventHeaderEnumerator = reader.GetEventHeaderEnumerator().

  • Call reader.OpenFile(perfDataFileName, sortOrder) to open the perf.data file and read the file header.

    • The sortOrder parameter specifies whether the reader should return events in the order they occur in the file (PerfDataFileEventOrder.File, less resource-intensive) or in timestamp order (PerfDataFileEventOrder.Time).

  • Call reader.ReadEvent(out eventBytes) to read the header and bytes of the next event.

  • Use eventBytes.Header.Type to determine the type of event.

  • If Type != Sample, this is a non-sample event that contains information about the trace or about the system on which the trace was collected. This library provides no support for decoding these events. Refer to linux/uapi/linux/perf_event.h for the format of these events.

    • Some of these events may have associated metadata, e.g. timestamp, CPU, pid, tid. This library does provide support for accessing the metadata by calling reader.GetNonSampleEventInfo(eventBytes, out nonSampleEventInfo).

  • If Type == Sample, this is a sample event, e.g. a tracepoint event.

    • Use reader.GetSampleEventInfo(eventBytes, out sampleEventInfo) to look up metadata for the event. If metadata lookup succeeds and sampleEventInfo.Format is not null, you can use this library to decode the event.

    • If sampleEventInfo.Format.DecodingStyle is TraceEventFormat, decode the event using sampleEventInfo.Format.Fields. Use sampleEventInfo.Format.Fields[i].GetFieldValue(sampleEventInfo) to get a PerfItemValue for the field at index i. The PerfItemValue has the field's type information and a ReadOnlySpan<byte> with the field's value. It also has helper methods for accessing the field's value as a .NET type or as a string. (The first Format.CommonFieldCount fields are usually not interesting and are typically skipped.)

    • If sampleEventInfo.Format.DecodingStyle is EventHeader, decode the event using eventHeaderEnumerator. Start enumeration by calling eventHeaderEnumerator.StartEvent(sampleEventInfo). You can then get EventHeader-specific information about the event from eventHeaderEnumerator.GetEventInfo(), and you can iterate through the fields of the event using eventHeaderEnumerator.MoveNext().

Classes and structs

  • EventHeaderEnumerator class - provides access to information and field values of an event that uses the EventHeader decoding format. This can be used in combination with the PerfDataFileReader class to read and decode events from a perf.data file, or with some other source of event data.

  • EventHeaderEventInfo struct - provides information about an EventHeader event, such as the tracepoint name, event name, severity level, activity ID, etc.

  • EventHeaderItemInfo struct - provides information about a field in an EventHeader event, such as the field name, field type, and field value.

  • PerfByteReader struct - helper for reading values from a data source that may be big-endian or little-endian, e.g. events from a perf.data file.

  • PerfConvert static class - provides methods for converting tracepoint event field data to .NET types.

    • Helpers for formatting fields as text (new string with ToString(), append to StringBuilder, or format to Span<char>).
    • Helpers for converting UNIX time_32 and time_64 timestamps to .NET DateTime values.

  • PerfDataFileReader class - parses a perf.data file into headers and events (optionally sorted by timestamp), provides access to event metadata like timestamp or CPU, tracks tracefs format decoding information for each event.

  • PerfEventBytes struct - bytes of a single event from a perf.data file.

  • PerfEventDesc class - stores the perf_event_attr, tracepoint name, and tracefs format information for a set of events.

  • PerfEventFormat class - parses a tracefs format file and provides access to the decoding information for tracepoint events.

  • PerfFieldFormat class - parses a field format string from a tracefs format file and provides access to the field name, type, and size.

  • PerfNonSampleEventInfo struct - provides information about a non-sample event, such as the event bytes, session information, cpu, time, pid, tracepoint name, format, and timestamp.

  • PerfSampleEventInfo struct - provides information about a sample event, such as the event bytes, session information, cpu, time, pid, tracepoint name, format, timestamp, raw, and format.

  • PerfSessionInfo class - provides information about a trace decoding session such as the byte order and the clock source.

  • PerfTimeSpec struct - represents a timestamp as a time64_t plus nanoseconds. Semantics equivalent to struct timespec from time.h.

  • PerfItemValue struct - represents the value of a field of a tracepoint event. Includes type information. Provides byte-order-aware helpers for accessing the value as a .NET type (e.g. GetU32, GetF64, GetGuid). Provides helpers for formatting the value as a string or appending it to a StringBuilder.

Project

This component is a part of the LinuxTracepoints-Net project. Feedback and contributions are welcome.

Changelog

0.2.0 (2024-06-19)

  • Renamed PerfItemType to PerfItemMetadata. Renamed corresponding methods and properties, GetItemType() ==> GetItemMetadata(), PerfItemValue.Type ==> PerfItemValue.Metadata.
  • Fixed incorrect PerfItemType.ElementCount value for struct element.
  • Fixed handling of nul-terminated strings that are not terminated before end of the event. Old behavior would treat field as invalid. New behavior treats field as terminated at end of event.
  • Fixed some comments that had been corrupted by over-active search-and-replace (i.e. Visual Studio rename incorrectly updated them).
  • Renamed item metadata's ArrayFlags property to ArrayFlag since only one flag should be set at a time.
  • Added item metadata IsScalar and IsElement properties.
  • Removed item metadata IsArrayOrElement and EncodingAndArrayFlags properties.
  • Added item value AppendJsonTo() method.
  • Moved AppendJsonEventIdentityTo() and AppendJsonEventInfoTo() methods from EventHeaderEnumerator to EventHeaderEventInfo.
  • Renamed "info" suffix to "meta". Renamed AppendJsonEventInfoTo to AppendJsonEventMetaTo, PerfInfoOptionstoPerfMetaOptions`, etc.
  • Add support for BinaryLength16Char8 encoding.
  • Add support for extended formats for StringLength16Char8 encoding.
  • Add support for IPAddress format.

0.1.3 (2024-05-20)

  • Fix error when using GetSampleEventInfo or GetNonSampleEventInfo with C# language 11 or later.
  • Formatting functions fall back to system/tracepoint name from format info if the system/tracepoint name is not available from the EVENT_DESC header (e.g. AppendJsonEventInfoTo, AppendJsonEventIdentityTo, ToString). Provide helpers to make it easier for clients to have the same fallback behavior.

0.1.2 (2024-05-06)

  • Fix invalid TID returned from GetNonSampleEventInfo.
  • Fix PerfTimeSpec.ToString() to properly include subsecond values.
  • Renamed PerfValue to PerfItemValue.
  • Refactored some of the PerfItemValue fields into a separate PerfItemType struct. Several perfItemValue.<property> members are now accessed as perfItemValue.Type.<property>: ElementCount, FieldTag, TypeSize, Encoding, ArrayFlags, EncodingAndArrayFlags, IsArrayOrElement, Format, StructFieldCount.
  • PerfSampleEventInfo.Format is now non-nullable. In cases where it was previously null, it now holds the Empty format (format.IsEmpty is true).
  • EventHeaderEnumerator now has a GetItemType() method. This returns a subset of the information returned from GetItemInfo() and can be used as an optimization when only the item type information is needed.
  • PerfConvert string methods have been refactored to ensure that callers correctly handle control characters (space, newline, etc.) when formatting strings (the new methods have a required parameter to indicate how control characters should be formatted - as-is, as-space, or as-escape-sequence). StringAppend is now StringAppendWithControlChars, and StringLatin1Append is now StringLatin1AppendWithControlChars. Default control character handling is replace-with-space for basic formatting and replace-with-JSON-escape-sequence for JSON formatting.
  • PerfConvert exposes several new methods: ReadGuidBigEndian, Char16AppendWithControlChars, etc.
  • PerfDataFileReader exposes new property SessionInfo.
  • PerfDataFileReader exposes new method HeaderString.
  • Added AsString extension method for PerfEventAttrType.
  • PerfTimeSpec now implements IComparable, IEquatable, and overloads the comparison operators.
  • PerfTimeSpec can now be constructed from a DateTime.
  • PerfTimeSpec exposes an AddNanoseconds method.

0.1.1 (2024-04-22)

  • Initial release.