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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Declaration of a Windows event trace provider class, to allow using
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// Windows Event Tracing for logging transport and control.
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#ifndef BASE_WIN_EVENT_TRACE_PROVIDER_H_
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#define BASE_WIN_EVENT_TRACE_PROVIDER_H_
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#include "base/base_export.h"
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#include "base/basictypes.h"
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typedef GUID EtwEventClass;
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typedef UCHAR EtwEventType;
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typedef UCHAR EtwEventLevel;
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typedef USHORT EtwEventVersion;
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typedef ULONG EtwEventFlags;
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// Base class is a POD for correctness.
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template <size_t N> struct EtwMofEventBase {
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EVENT_TRACE_HEADER header;
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// Utility class to auto-initialize event trace header structures.
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template <size_t N> class EtwMofEvent: public EtwMofEventBase<N> {
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typedef EtwMofEventBase<N> Super;
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// Clang and the C++ standard don't allow unqualified lookup into dependent
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// bases, hence these using decls to explicitly pull the names out.
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using EtwMofEventBase<N>::header;
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using EtwMofEventBase<N>::fields;
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memset(static_cast<Super*>(this), 0, sizeof(Super));
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EtwMofEvent(const EtwEventClass& event_class, EtwEventType type,
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EtwEventLevel level) {
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memset(static_cast<Super*>(this), 0, sizeof(Super));
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header.Size = sizeof(Super);
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header.Guid = event_class;
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header.Class.Type = type;
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header.Class.Level = level;
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header.Flags = WNODE_FLAG_TRACED_GUID | WNODE_FLAG_USE_MOF_PTR;
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EtwMofEvent(const EtwEventClass& event_class, EtwEventType type,
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EtwEventVersion version, EtwEventLevel level) {
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memset(static_cast<Super*>(this), 0, sizeof(Super));
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header.Size = sizeof(Super);
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header.Guid = event_class;
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header.Class.Type = type;
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header.Class.Version = version;
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header.Class.Level = level;
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header.Flags = WNODE_FLAG_TRACED_GUID | WNODE_FLAG_USE_MOF_PTR;
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void SetField(int field, size_t size, const void *data) {
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if ((field < N) && (size <= kuint32max)) {
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fields[field].DataPtr = reinterpret_cast<ULONG64>(data);
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fields[field].Length = static_cast<ULONG>(size);
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EVENT_TRACE_HEADER* get() { return& header; }
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DISALLOW_COPY_AND_ASSIGN(EtwMofEvent);
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// Trace provider with Event Tracing for Windows. The trace provider
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// registers with ETW by its name which is a GUID. ETW calls back to
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// the object whenever the trace level or enable flags for this provider
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// Users of this class can test whether logging is currently enabled at
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// a particular trace level, and whether particular enable flags are set,
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// before other resources are consumed to generate and issue the log
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// messages themselves.
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class BASE_EXPORT EtwTraceProvider {
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// Creates an event trace provider identified by provider_name, which
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// will be the name registered with Event Tracing for Windows (ETW).
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explicit EtwTraceProvider(const GUID& provider_name);
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// Creates an unnamed event trace provider, the provider must be given
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// a name before registration.
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virtual ~EtwTraceProvider();
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// Registers the trace provider with Event Tracing for Windows.
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// Note: from this point forward ETW may call the provider's control
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// callback. If the provider's name is enabled in some trace session
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// already, the callback may occur recursively from this call, so
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// call this only when you're ready to handle callbacks.
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// Unregisters the trace provider with ETW.
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void set_provider_name(const GUID& provider_name) {
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provider_name_ = provider_name;
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const GUID& provider_name() const { return provider_name_; }
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TRACEHANDLE registration_handle() const { return registration_handle_; }
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TRACEHANDLE session_handle() const { return session_handle_; }
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EtwEventFlags enable_flags() const { return enable_flags_; }
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EtwEventLevel enable_level() const { return enable_level_; }
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// Returns true iff logging should be performed for "level" and "flags".
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// Note: flags is treated as a bitmask, and should normally have a single
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// bit set, to test whether to log for a particular sub "facility".
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bool ShouldLog(EtwEventLevel level, EtwEventFlags flags) {
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return NULL != session_handle_ && level >= enable_level_ &&
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(0 != (flags & enable_flags_));
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// Simple wrappers to log Unicode and ANSI strings.
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// Do nothing if !ShouldLog(level, 0xFFFFFFFF).
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ULONG Log(const EtwEventClass& event_class, EtwEventType type,
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EtwEventLevel level, const char *message);
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ULONG Log(const EtwEventClass& event_class, EtwEventType type,
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EtwEventLevel level, const wchar_t *message);
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// Log the provided event.
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ULONG Log(EVENT_TRACE_HEADER* event);
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// Called after events have been enabled, override in subclasses
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// to set up state or log at the start of a session.
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// Note: This function may be called ETW's thread and may be racy,
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// bring your own locking if needed.
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virtual void OnEventsEnabled() {}
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// Called just before events are disabled, override in subclasses
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// to tear down state or log at the end of a session.
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// Note: This function may be called ETW's thread and may be racy,
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// bring your own locking if needed.
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virtual void OnEventsDisabled() {}
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// Called just after events have been disabled, override in subclasses
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// to tear down state at the end of a session. At this point it's
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// to late to log anything to the session.
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// Note: This function may be called ETW's thread and may be racy,
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// bring your own locking if needed.
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virtual void PostEventsDisabled() {}
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ULONG EnableEvents(PVOID buffer);
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ULONG DisableEvents();
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ULONG Callback(WMIDPREQUESTCODE request, PVOID buffer);
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static ULONG WINAPI ControlCallback(WMIDPREQUESTCODE request, PVOID context,
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ULONG *reserved, PVOID buffer);
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TRACEHANDLE registration_handle_;
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TRACEHANDLE session_handle_;
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EtwEventFlags enable_flags_;
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EtwEventLevel enable_level_;
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// We don't use this, but on XP we're obliged to pass one in to
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// RegisterTraceGuids. Non-const, because that's how the API needs it.
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static TRACE_GUID_REGISTRATION obligatory_guid_registration_;
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DISALLOW_COPY_AND_ASSIGN(EtwTraceProvider);
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#endif // BASE_WIN_EVENT_TRACE_PROVIDER_H_