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trace: Add a basic event-tracing infrastructure.
This commit adds the src/trace directory containing the basics for our tracing subsystem. It is not used in the code base. The "src/trace/debug.h" file contains an example on how we can map our tor trace events to log_debug(). The tracing subsystem can only be enabled by tracing framework at compile time. This commit introduces the "--enable-tracing-debug" option that will make all "tor_trace()" function be maped to "log_debug()". Closes #13802 Signed-off-by: David Goulet <dgoulet@torproject.org>
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3
.gitignore
vendored
3
.gitignore
vendored
@ -125,6 +125,9 @@ uptime-*.json
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/src/Makefile
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/src/Makefile.in
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# /src/trace
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/src/trace/libor-trace.a
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# /src/common/
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/src/common/Makefile
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/src/common/Makefile.in
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5
changes/ticket13802
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5
changes/ticket13802
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@ -0,0 +1,5 @@
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o Minor features (testing):
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- Add general tracing instrumentation to Tor. For now, this subsystem is
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not being used by any part of the code, it is for future use or external
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testing that is not part of the upstream code base. Any tracing
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framework needs to be enabled at compile time. Closes #13802.
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10
configure.ac
10
configure.ac
@ -189,6 +189,16 @@ AC_ARG_ENABLE(seccomp,
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AC_ARG_ENABLE(libscrypt,
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AS_HELP_STRING(--disable-libscrypt, [do not attempt to use libscrypt]))
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dnl Enable event tracing which are transformed to debug log statement.
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AC_ARG_ENABLE(event-tracing-debug,
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AS_HELP_STRING(--enable-event-tracing-debug, [build with event tracing to debug log]))
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AM_CONDITIONAL([USE_EVENT_TRACING_DEBUG], [test "x$enable_event_tracing_debug" = "xyes"])
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if test x$enable_event_tracing_debug = xyes; then
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AC_DEFINE([USE_EVENT_TRACING_DEBUG], [1], [Tracing framework to log debug])
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AC_DEFINE([TOR_EVENT_TRACING_ENABLED], [1], [Compile the event tracing instrumentation])
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fi
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dnl check for the correct "ar" when cross-compiling.
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dnl (AM_PROG_AR was new in automake 1.11.2, which we do not yet require,
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dnl so kludge up a replacement for the case where it isn't there yet.)
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90
doc/HACKING/Tracing.md
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doc/HACKING/Tracing.md
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@ -0,0 +1,90 @@
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# Tracing #
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This document describes how the tracing subsystem works in tor so developers
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can add events to the code base but also hook them to a tracing framework.
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## Basics ###
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Tracing is seperated in two concepts, trace events and a tracer. The tracing
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subsystem can be found in `src/trace`. The `events.h` header file is the
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main file that maps the different tracers to trace events.
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### Events ###
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A trace event is basically a function from which we can pass any data that
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we want to collect. In addition, we specify a context for the event such as
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a subsystem and an event name.
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A trace event in tor has the following standard format:
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tor_trace(subsystem, event\_name, args...)
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The `subsystem` parameter is the name of the subsytem the trace event is in.
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For example that could be "scheduler" or "vote" or "hs". The idea is to add
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some context to the event so when we collect them we know where it's coming
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from. The `event_name` is the name of the event which helps a lot with
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adding some semantic to the event. Finally, `args` is any number of
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arguments we want to collect.
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Here is an example of a possible tracepoint in main():
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tor_trace(main, init_phase, argc)
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The above is a tracepoint in the `main` subsystem with `init_phase` as the
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event name and the `int argc` is passed to the event as well.
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How `argc` is collected or used has nothing to do with the instrumentation
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(adding trace events to the code). It is the work of the tracer so this is why
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the trace events and collection framework (tracer) are decoupled. You _can_
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have trace events without a tracer.
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### Tracer ###
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In `src/trace/events.h`, we map the `tor_trace()` function to the right
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tracer. A tracer support is only enabled at compile time. For instance, the
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file `src/trace/debug.h` contains the mapping of the generic tracing function
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`tor_trace()` to the `log_debug()` function. More specialized function can be
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mapped depending on the tracepoint.
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## Build System ##
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This section describes how it is integrated into the build system of tor.
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By default, every tracing events are disabled in tor that is `tor_trace()`
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is a NOP.
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To enable a tracer, there is a configure option on the form of:
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--enable-tracing-<tracer>
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We have an option that will send every trace events to a `log_debug()` (as
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mentionned above) which will print you the subsystem and name of the event but
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not the arguments for technical reasons. This is useful if you want to quickly
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see if your trace event is being hit or well written. To do so, use this
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configure option:
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--enable-tracing-debug
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## Instrument Tor ##
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This is pretty easy. Let's say you want to add a trace event in
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`src/or/rendcache.c`, you only have to add this include statement:
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#include "trace/events.h"
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Once done, you can add as many as you want `tor_trace()` that you need.
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Please use the right subsystem (here it would be `hs`) and a unique name that
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tells what the event is for. For example:
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tor_trace(hs, store_desc_as_client, desc, desc_id);
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If you look in `src/trace/events.h`, you'll see that if tracing is enabled it
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will be mapped to a function called:
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tor_trace_hs_store_desc_as_client(desc, desc_id)
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And the point of all this is for that function to be defined in a new file
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that you might want to add named `src/trace/hs.{c|h}` which would defined how
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to collect the data for the `tor_trace_hs_store_desc_as_client()` function
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like for instance sending it to a `log_debug()` or do more complex operations
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or use a userspace tracer like LTTng (https://lttng.org).
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@ -7,3 +7,4 @@ include src/tools/include.am
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include src/win32/include.am
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include src/config/include.am
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include src/test/fuzz/include.am
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include src/trace/include.am
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@ -120,6 +120,7 @@ src_or_tor_LDFLAGS = @TOR_LDFLAGS_zlib@ @TOR_LDFLAGS_openssl@ @TOR_LDFLAGS_libev
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src_or_tor_LDADD = src/or/libtor.a src/common/libor.a src/common/libor-ctime.a \
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src/common/libor-crypto.a $(LIBKECCAK_TINY) $(LIBDONNA) \
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src/common/libor-event.a src/trunnel/libor-trunnel.a \
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src/trace/libor-trace.a \
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@TOR_ZLIB_LIBS@ @TOR_LIB_MATH@ @TOR_LIBEVENT_LIBS@ @TOR_OPENSSL_LIBS@ \
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@TOR_LIB_WS32@ @TOR_LIB_GDI@ @CURVE25519_LIBS@ @TOR_SYSTEMD_LIBS@ \
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@TOR_LZMA_LIBS@ @TOR_ZSTD_LIBS@
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@ -193,6 +193,7 @@ src_test_test_LDADD = src/or/libtor-testing.a \
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src/common/libor-ctime-testing.a \
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src/common/libor-event-testing.a \
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src/trunnel/libor-trunnel-testing.a \
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src/trace/libor-trace.a \
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@TOR_ZLIB_LIBS@ @TOR_LIB_MATH@ @TOR_LIBEVENT_LIBS@ \
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@TOR_OPENSSL_LIBS@ @TOR_LIB_WS32@ @TOR_LIB_GDI@ @CURVE25519_LIBS@ \
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@TOR_SYSTEMD_LIBS@ @TOR_LZMA_LIBS@ @TOR_ZSTD_LIBS@
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@ -216,6 +217,7 @@ src_test_bench_LDADD = src/or/libtor.a src/common/libor.a \
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src/common/libor-ctime.a \
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src/common/libor-crypto.a $(LIBKECCAK_TINY) $(LIBDONNA) \
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src/common/libor-event.a src/trunnel/libor-trunnel.a \
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src/trace/libor-trace.a \
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@TOR_ZLIB_LIBS@ @TOR_LIB_MATH@ @TOR_LIBEVENT_LIBS@ \
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@TOR_OPENSSL_LIBS@ @TOR_LIB_WS32@ @TOR_LIB_GDI@ @CURVE25519_LIBS@ \
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@TOR_SYSTEMD_LIBS@ @TOR_LZMA_LIBS@ @TOR_ZSTD_LIBS@
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@ -227,6 +229,7 @@ src_test_test_workqueue_LDADD = src/or/libtor-testing.a \
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src/common/libor-ctime-testing.a \
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src/common/libor-crypto-testing.a $(LIBKECCAK_TINY) $(LIBDONNA) \
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src/common/libor-event-testing.a \
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src/trace/libor-trace.a \
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@TOR_ZLIB_LIBS@ @TOR_LIB_MATH@ @TOR_LIBEVENT_LIBS@ \
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@TOR_OPENSSL_LIBS@ @TOR_LIB_WS32@ @TOR_LIB_GDI@ @CURVE25519_LIBS@ \
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@TOR_LZMA_LIBS@ @TOR_ZSTD_LIBS@
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@ -264,6 +267,7 @@ src_test_test_ntor_cl_LDFLAGS = @TOR_LDFLAGS_zlib@ @TOR_LDFLAGS_openssl@
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src_test_test_ntor_cl_LDADD = src/or/libtor.a src/common/libor.a \
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src/common/libor-ctime.a \
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src/common/libor-crypto.a $(LIBKECCAK_TINY) $(LIBDONNA) \
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src/trace/libor-trace.a \
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@TOR_ZLIB_LIBS@ @TOR_LIB_MATH@ \
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@TOR_OPENSSL_LIBS@ @TOR_LIB_WS32@ @TOR_LIB_GDI@ @CURVE25519_LIBS@ \
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@TOR_LZMA_LIBS@
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@ -285,6 +289,7 @@ noinst_PROGRAMS += src/test/test-bt-cl
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src_test_test_bt_cl_SOURCES = src/test/test_bt_cl.c
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src_test_test_bt_cl_LDADD = src/common/libor-testing.a \
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src/common/libor-ctime-testing.a \
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src/trace/libor-trace.a \
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@TOR_LIB_MATH@ \
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@TOR_LIB_WS32@ @TOR_LIB_GDI@
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src_test_test_bt_cl_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS)
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25
src/trace/debug.h
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src/trace/debug.h
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/* Copyright (c) 2017, The Tor Project, Inc. */
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/* See LICENSE for licensing information */
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#ifndef TOR_TRACE_LOG_DEBUG_H
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#define TOR_TRACE_LOG_DEBUG_H
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#include "torlog.h"
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/* Stringify pre-processor trick. */
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#define XSTR(d) STR(d)
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#define STR(s) #s
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/* Send every event to a debug log level. This is useful to debug new trace
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* events without implementing them for a specific event tracing framework.
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* Note that the arguments are ignored since at this step we do not know the
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* types and amount there is. */
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/* Example on how to map a tracepoint to log_debug(). */
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#undef tor_trace
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#define tor_trace(subsystem, name, args...) \
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log_debug(LD_GENERAL, "Trace event \"" XSTR(name) "\" from " \
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"\"" XSTR(subsystem) "\" hit. " \
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"(line "XSTR(__LINE__) ")")
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#endif /* TOR_TRACE_LOG_DEBUG_H */
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src/trace/events.h
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src/trace/events.h
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/* Copyright (c) 2017, The Tor Project, Inc. */
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/* See LICENSE for licensing information */
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/**
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* \file events.h
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* \brief Header file for Tor event tracing.
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**/
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#ifndef TOR_TRACE_EVENTS_H
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#define TOR_TRACE_EVENTS_H
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/*
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* The following defines a generic event tracing function name that has to be
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* used to trace events in the code base.
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*
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* That generic function is then defined by a event tracing framework. For
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* instance, the "log debug" framework sends all trace events to log_debug()
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* which is defined in src/trace/debug.h which can only be enabled at compile
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* time (--enable-event-tracing-debug).
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*
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* By default, every trace events in the code base are replaced by a NOP. See
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* doc/HACKING/Tracing.md for more information on how to use event tracing or
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* add events.
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*/
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#ifdef TOR_EVENT_TRACING_ENABLED
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/* Map every trace event to a per subsystem macro. */
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#define tor_trace(subsystem, name, ...) \
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tor_trace_##subsystem(name, __VA_ARGS__)
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/* Enable event tracing for the debug framework where all trace events are
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* mapped to a log_debug(). */
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#ifdef USE_EVENT_TRACING_DEBUG
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#include "trace/debug.h"
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#endif
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#else /* TOR_EVENT_TRACING_ENABLED */
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/* Reaching this point, we NOP every event declaration because event tracing
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* is not been enabled at compile time. */
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#define tor_trace(subsystem, name, args...)
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#endif /* TOR_EVENT_TRACING_ENABLED */
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#endif /* TOR_TRACE_EVENTS_H */
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src/trace/include.am
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# Include the src/ so we can use the trace/events.h statement when including
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# any file in that directory.
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AM_CPPFLAGS += -I$(srcdir)/src
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noinst_LIBRARIES += \
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src/trace/libor-trace.a
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LIBOR_TRACE_A_SOURCES =
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TRACEHEADERS = \
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src/trace/events.h
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if USE_EVENT_TRACING_DEBUG
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TRACEHEADERS += \
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src/trace/debug.h
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endif
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# Library source files.
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src_trace_libor_trace_a_SOURCES = $(LIBOR_TRACE_A_SOURCES)
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noinst_HEADERS+= $(TRACEHEADERS)
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