Improve ETW callback support and track provider enable state

pkg/etw/provider.go

@@ -3,6 +3,7 @@ package etw
 import (
 	"bytes"
 	"encoding/binary"
+	"sync"
 	"unsafe"
 
 	"golang.org/x/sys/windows"
@@ -20,8 +21,14 @@ const (
 // name and ID (GUID), which should always have a 1:1 mapping to each other
 // (e.g. don't use multiple provider names with the same ID, or vice versa).
 type Provider struct {
-	handle   providerHandle
-	metadata []byte
+	handle     providerHandle
+	metadata   []byte
+	callback   EnableCallback
+	index      uint
+	enabled    bool
+	level      Level
+	keywordAny uint64
+	keywordAll uint64
 }
 
 type providerHandle windows.Handle
@@ -61,18 +68,87 @@ func (descriptor *eventDataDescriptor) set(dataType eventDataDescriptorType, buf
 	descriptor.dataType = dataType
 }
 
-// NewProvider creates and registers a new provider.
-func NewProvider(name string, id *windows.GUID, callback EnableCallback) (*Provider, error) {
-	provider := &Provider{}
+// Because the provider callback function needs to be able to access the
+// provider data when it is invoked by ETW, we need to keep provider data stored
+// in a global map based on an index. The index is passed as the callback
+// context to ETW.
+type providerMap struct {
+	m    map[uint]*Provider
+	i    uint
+	lock sync.Mutex
+}
 
-	innerCallback := func(sourceID *windows.GUID, state ProviderState, level Level, matchAnyKeyword uint64, matchAllKeyword uint64, filterData uintptr, _ uintptr) uintptr {
-		if callback != nil {
-			callback(sourceID, state, level, matchAnyKeyword, matchAllKeyword, filterData)
-		}
-		return 0
+var providers = providerMap{
+	m: make(map[uint]*Provider),
+}
+
+func (p *providerMap) newProvider() *Provider {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	i := p.i
+	p.i++
+
+	provider := &Provider{
+		index: i,
 	}
 
-	if err := eventRegister(id, windows.NewCallback(innerCallback), 0, &provider.handle); err != nil {
+	p.m[i] = provider
+	return provider
+}
+
+func (p *providerMap) removeProvider(provider *Provider) {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	delete(p.m, provider.index)
+}
+
+func (p *providerMap) getProvider(index uint) *Provider {
+	p.lock.Lock()
+	defer p.lock.Unlock()
+
+	return p.m[index]
+}
+
+func providerCallback(sourceID *windows.GUID, state ProviderState, level Level, matchAnyKeyword uint64, matchAllKeyword uint64, filterData uintptr, i uintptr) {
+	provider := providers.getProvider(uint(i))
+
+	switch state {
+	case ProviderStateDisable:
+		provider.enabled = false
+	case ProviderStateEnable:
+		provider.enabled = true
+		provider.level = level
+		provider.keywordAny = matchAnyKeyword
+		provider.keywordAll = matchAllKeyword
+	}
+
+	if provider.callback != nil {
+		provider.callback(sourceID, state, level, matchAnyKeyword, matchAllKeyword, filterData)
+	}
+}
+
+// providerCallbackAdapter acts as the first-level callback from the C/ETW side
+// for provider notifications. Because Go has trouble with callback arguments of
+// different size, it has only pointer-sized arguments, which are then cast to
+// the appropriate types when calling providerCallback.
+func providerCallbackAdapter(sourceID *windows.GUID, state uintptr, level uintptr, matchAnyKeyword uintptr, matchAllKeyword uintptr, filterData uintptr, i uintptr) uintptr {
+	providerCallback(sourceID, ProviderState(state), Level(level), uint64(matchAnyKeyword), uint64(matchAllKeyword), filterData, i)
+	return 0
+}
+
+// NewProvider creates and registers a new provider.
+func NewProvider(name string, id *windows.GUID, callback EnableCallback) (provider *Provider, err error) {
+	provider = providers.newProvider()
+	defer func() {
+		if err != nil {
+			providers.removeProvider(provider)
+		}
+	}()
+	provider.callback = callback
+
+	if err := eventRegister(id, windows.NewCallback(providerCallbackAdapter), uintptr(provider.index), &provider.handle); err != nil {
 		return nil, err
 	}
 
@@ -88,9 +164,45 @@ func NewProvider(name string, id *windows.GUID, callback EnableCallback) (*Provi
 
 // Close unregisters the provider.
 func (provider *Provider) Close() error {
+	providers.removeProvider(provider)
 	return eventUnregister(provider.handle)
 }
 
+// IsEnabled calls IsEnabledForLevelAndKeywords with LevelAlways and all
+// keywords set.
+func (provider *Provider) IsEnabled() bool {
+	return provider.IsEnabledForLevelAndKeywords(LevelAlways, ^uint64(0))
+}
+
+// IsEnabledForLevel calls IsEnabledForLevelAndKeywords with the specified level
+// and all keywords set.
+func (provider *Provider) IsEnabledForLevel(level Level) bool {
+	return provider.IsEnabledForLevelAndKeywords(level, ^uint64(0))
+}
+
+// IsEnabledForLevelAndKeywords allows event producer code to check if there are
+// any event sessions that are interested in an event, based on the event level
+// and keywords. Although this check happens automatically in the ETW
+// infrastructure, it can be useful to check if an event will actually be
+// consumed before doing expensive work to build the event data.
+func (provider *Provider) IsEnabledForLevelAndKeywords(level Level, keywords uint64) bool {
+	if !provider.enabled {
+		return false
+	}
+
+	// ETW automatically sets the level to 255 if it is specified as 0, so we
+	// don't need to worry about the level=0 (all events) case.
+	if level > provider.level {
+		return false
+	}
+
+	if keywords != 0 && (keywords&provider.keywordAny == 0 || keywords&provider.keywordAll != provider.keywordAll) {
+		return false
+	}
+
+	return true
+}
+
 // WriteEvent writes a single event to ETW, from this provider.
 func (provider *Provider) WriteEvent(event *Event) error {
 	// Finalize the event metadata buffer by filling in the buffer length at the

pkg/etwlogrus/hook.go

@@ -44,6 +44,10 @@ func (h *Hook) Levels() []logrus.Level {
 
 // Fire receives each Logrus entry as it is logged, and logs it to ETW.
 func (h *Hook) Fire(e *logrus.Entry) error {
+	if !h.provider.IsEnabledForLevel(etw.Level(e.Level)) {
+		return
+	}
+
 	descriptor := etw.NewEventDescriptor()
 
 	// We could try to map Logrus levels to ETW levels, but we would lose some