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decoder.go
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decoder.go
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// Copyright 2017 Capsule8, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package perf
import (
"encoding/binary"
"errors"
"fmt"
"sync"
"sync/atomic"
)
// TraceEventSampleData is a type alias for map[string]interface{}, which is
// the representation of sample data parsed from a Linux kernel sample.
type TraceEventSampleData map[string]interface{}
// TraceEventDecoderFn is the signature of a function to call to decode a
// sample. The first argument is the sample to be decoded, and the second
// is the parsed sample data.
type TraceEventDecoderFn func(*SampleRecord, TraceEventSampleData) (interface{}, error)
type traceEventDecoder struct {
fields map[string]traceEventField
decoderfn TraceEventDecoderFn
}
func newTraceEventDecoder(name string, fn TraceEventDecoderFn) (*traceEventDecoder, uint16, error) {
id, fields, err := getTraceEventFormat(name)
if err != nil {
return nil, 0, err
}
decoder := &traceEventDecoder{
fields: fields,
decoderfn: fn,
}
return decoder, id, err
}
func decodeDataType(dataType int, rawData []byte) (interface{}, error) {
switch dataType {
case dtString:
return nil, errors.New("internal error; got unexpected dtString")
case dtS8:
return int8(rawData[0]), nil
case dtS16:
return int16(binary.LittleEndian.Uint16(rawData)), nil
case dtS32:
return int32(binary.LittleEndian.Uint32(rawData)), nil
case dtS64:
return int64(binary.LittleEndian.Uint64(rawData)), nil
case dtU8:
return uint8(rawData[0]), nil
case dtU16:
return binary.LittleEndian.Uint16(rawData), nil
case dtU32:
return binary.LittleEndian.Uint32(rawData), nil
case dtU64:
return binary.LittleEndian.Uint64(rawData), nil
}
return nil, errors.New("internal error; undefined dataType")
}
func (d *traceEventDecoder) decodeRawData(rawData []byte) (TraceEventSampleData, error) {
data := make(TraceEventSampleData)
for _, field := range d.fields {
var arraySize, dataLength, dataOffset int
var err error
if field.dataLocSize > 0 {
switch field.dataLocSize {
case 4:
dataOffset = int(binary.LittleEndian.Uint16(rawData[field.Offset:]))
dataLength = int(binary.LittleEndian.Uint16(rawData[field.Offset+2:]))
case 8:
dataOffset = int(binary.LittleEndian.Uint32(rawData[field.Offset:]))
dataLength = int(binary.LittleEndian.Uint32(rawData[field.Offset+4:]))
default:
return nil, fmt.Errorf("__data_loc size is neither 4 nor 8 (got %d)", field.dataLocSize)
}
if field.dataType == dtString {
if dataLength > 0 && rawData[dataOffset+dataLength-1] == 0 {
dataLength--
}
data[field.FieldName] = string(rawData[dataOffset : dataOffset+dataLength])
continue
}
arraySize = dataLength / field.dataTypeSize
} else if field.arraySize == 0 {
data[field.FieldName], err = decodeDataType(field.dataType, rawData[field.Offset:])
if err != nil {
return nil, err
}
continue
} else {
arraySize = field.arraySize
dataOffset = field.Offset
dataLength = arraySize * field.dataTypeSize
}
var array = make([]interface{}, arraySize)
for i := 0; i < arraySize; i++ {
array[i], err = decodeDataType(field.dataType, rawData[dataOffset:])
if err != nil {
return nil, err
}
dataOffset += field.dataTypeSize
}
data[field.FieldName] = array
}
return data, nil
}
type decoderMap struct {
decoders map[uint16]*traceEventDecoder
names map[string]uint16
}
func newDecoderMap() *decoderMap {
return &decoderMap{
decoders: make(map[uint16]*traceEventDecoder),
names: make(map[string]uint16),
}
}
func (dm *decoderMap) add(name string, id uint16, decoder *traceEventDecoder) {
dm.decoders[id] = decoder
dm.names[name] = id
}
type traceEventDecoderMap struct {
sync.Mutex // used only by writers
active atomic.Value // *decoderMap
}
func (m *traceEventDecoderMap) getDecoderMap() *decoderMap {
value := m.active.Load()
if value == nil {
return nil
}
return value.(*decoderMap)
}
func newTraceEventDecoderMap() *traceEventDecoderMap {
return &traceEventDecoderMap{}
}
// Add a decoder "in-place". i.e., don't copy the decoder map before update
// No synchronization is used. Assumes the caller has adequate protection
func (m *traceEventDecoderMap) addDecoderInPlace(name string, fn TraceEventDecoderFn) (uint16, error) {
decoder, id, err := newTraceEventDecoder(name, fn)
if err != nil {
return 0, err
}
dm := m.getDecoderMap()
if dm == nil {
dm = newDecoderMap()
m.active.Store(dm)
}
dm.add(name, id, decoder)
return id, nil
}
// Add a decoder safely. Proper synchronization is used to prevent multiple
// writers from stomping on each other while allowing readers to always
// operate without locking
func (m *traceEventDecoderMap) AddDecoder(name string, fn TraceEventDecoderFn) (uint16, error) {
decoder, id, err := newTraceEventDecoder(name, fn)
if err != nil {
return 0, err
}
m.Lock()
defer m.Unlock()
odm := m.getDecoderMap()
ndm := newDecoderMap()
if odm != nil {
for k, v := range odm.decoders {
ndm.decoders[k] = v
}
for k, v := range odm.names {
ndm.names[k] = v
}
}
ndm.add(name, id, decoder)
m.active.Store(ndm)
return id, nil
}
// Remove a decoder "in-place". i.e., don't copy the decoder map before update
// No synchronization is used. Assumes the caller has adequate protection
func (m *traceEventDecoderMap) removeDecoderInPlace(name string) {
dm := m.getDecoderMap()
if dm == nil {
return
}
id, ok := dm.names[name]
if ok {
delete(dm.names, name)
delete(dm.decoders, id)
}
}
// Remove a decoder safely. Proper synchronization is used to prevent multiple
// writers from stomping on each other while allowing readers to always
// operate without locking
func (m *traceEventDecoderMap) RemoveDecoder(name string) {
dm := m.getDecoderMap()
if dm == nil {
return
}
id, ok := dm.names[name]
if ok {
m.Lock()
defer m.Unlock()
odm := m.getDecoderMap()
if odm != nil {
ndm := newDecoderMap()
for k, v := range odm.decoders {
if k != id {
ndm.decoders[k] = v
}
}
for k, v := range odm.names {
if k != name {
ndm.names[k] = v
}
}
m.active.Store(ndm)
}
}
}
func (m *traceEventDecoderMap) getDecoder(eventType uint16) *traceEventDecoder {
dm := m.getDecoderMap()
if dm == nil {
return nil
}
return dm.decoders[eventType]
}
func (m *traceEventDecoderMap) DecodeSample(sample *SampleRecord) (interface{}, error) {
eventType := uint16(binary.LittleEndian.Uint64(sample.RawData))
decoder := m.getDecoder(eventType)
if decoder == nil {
// Not an error. There just isn't a decoder for this sample
return nil, nil
}
data, err := decoder.decodeRawData(sample.RawData)
if err != nil {
return nil, err
}
return decoder.decoderfn(sample, data)
}