Add support to send verbose messages to lttng

Support includes a test program and redirection of verbose output to the
lttng tracing system.

For adding lttng tracepoints to a library or application, the cmake macro
add_lttng_tracepoint() is available.

CMakeLists.txt

@@ -169,6 +169,17 @@ if(DBUS_LINUX)
     endif()
 endif()
 
+if(DBUS_LINUX)
+    option(ENABLE_VERBOSE_LTTNG "Enable redirecting verbose messages to lttng tracing systen" OFF)
+    if(ENABLE_VERBOSE_LTTNG)
+        pkg_check_modules(LTTNG lttng-ust)
+        if(LTTNG_FOUND)
+            set(HAVE_LTTNG 1)
+            message(STATUS "lttng found using ${LTTNG_LIBRARIES}")
+        endif()
+    endif()
+endif()
+
 if(NOT ENABLE_TRADITIONAL_ACTIVATION AND NOT (DBUS_LINUX AND DBUS_BUS_ENABLE_SYSTEMD))
     message(WARNING "\
 Traditional activation and systemd activation are both disabled, so service \

README-lttng.md

@@ -0,0 +1,82 @@
+# LTTNG support for dbus
+
+The lttng support for DBus allows verbose messages issued on the console
+on unix-like operating systems, when verbose mode is enabled at build time
+and the environment variable DBUS_VERBOSE=1 is set, to be redirected to the
+tracing system provided by lttng.
+
+This requires installing the development package for lttng-ust and building
+dbus with it by adding -DENABLE_VERBOSE_LTTNG=1 to the cmake configure line.
+
+For more details on lttng, see https://lttng.org/.
+
+## lttng example session
+```sh
+# create session
+$ lttng create dbus
+Session dbus created.
+Traces will be output to /home/user/lttng-traces/dbus-20230116-094713
+
+# activate session (only required when using multiple sessions)
+$ lttng set-session dbus
+
+# enable events
+$ lttng enable-event --userspace 'dbus:*'
+UST event dbus:* created in channel channel0
+
+# show session status (opptional)
+$ lttng status
+Tracing session dbus: [active]
+    Trace output: /home/user/lttng-traces/dbus-20230116-094713
+
+=== Domain: User space ===
+
+Buffering scheme: per-user
+
+Tracked process attributes
+  Virtual process IDs:  all
+  Virtual user IDs:     all
+  Virtual group IDs:    all
+
+Channels:
+-------------
+- channel0: [enabled]
+
+    Attributes:
+      Event-loss mode:  discard
+      Sub-buffer size:  524288 bytes
+      Sub-buffer count: 4
+      Switch timer:     inactive
+      Read timer:       inactive
+      Monitor timer:    1000000 us
+      Blocking timeout: 0 us
+      Trace file count: 1 per stream
+      Trace file size:  unlimited
+      Output mode:      mmap
+
+    Statistics:
+      Discarded events: 0
+
+    Event rules:
+      dbus:* (type: tracepoint) [enabled]
+
+# start tracing
+$ lttng start
+
+# run dbus app
+$ ../dbus-cmake-build/bin/test-lttng
+
+# stop tracing
+$ lttng stop
+Waiting for data availability.
+Tracing stopped for session dbus
+
+# show tracing results
+$ lttng view
+Trace directory: /home/user/lttng-traces/dbus-20230116-094713
+
+[10:34:22.255406515] (+?.?????????) host dbus:lttng_test: { cpu_id = 8 }, { my_integer_field = 1, my_string_field = "../dbus-cmake-build/bin/test-lttng" }
+
+# destroy session
+$ lttng destroy dbus
+```

cmake/modules/Macros.cmake

@@ -392,3 +392,24 @@ macro(add_systemd_service file)
         install_symlink(../${_name} ${_linkdir}/${_name})
     endforeach()
 endmacro()
+
+#
+# generate source files from lttng tracepoint template and add to target
+#
+# _target: target to add the generated sources
+# _tpfile: file with lttng tracepoint template
+#
+macro(add_lttng_tracepoint _target _tpfile)
+    string(REPLACE ".tp" "-tp.h" h_file ${_tpfile})
+    string(REPLACE ".tp" "-tp.c" c_file ${_tpfile})
+    get_filename_component(h_file ${h_file} NAME)
+    get_filename_component(c_file ${c_file} NAME)
+    add_custom_command(
+        OUTPUT ${c_file}
+        COMMAND lttng-gen-tp ${CMAKE_CURRENT_SOURCE_DIR}/${_tpfile} -o ${c_file} -o ${h_file}
+        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+        DEPENDS ${_tpfile}
+    )
+    set_source_files_properties(${h_file} ${c_file} PROPERTIES GENERATED 1)
+    target_sources(${_target} PRIVATE ${h_file} ${c_file} ${_tpfile})
+endmacro()

dbus/CMakeLists.txt

@@ -286,17 +286,23 @@ else(WIN32)
     if(DEFINED DBUS_LIBRARY_REVISION)
         set_target_properties(dbus-1 PROPERTIES VERSION ${DBUS_LIBRARY_MAJOR}.${DBUS_LIBRARY_AGE}.${DBUS_LIBRARY_REVISION} SOVERSION ${DBUS_LIBRARY_MAJOR})
     endif()
-    target_link_libraries(dbus-1 ${CMAKE_THREAD_LIBS_INIT} ${SYSTEMD_LIBRARIES})
+    target_link_libraries(dbus-1 PUBLIC ${CMAKE_THREAD_LIBS_INIT} ${SYSTEMD_LIBRARIES})
     if(LIBRT)
-        target_link_libraries(dbus-1 ${LIBRT})
+        target_link_libraries(dbus-1 PRIVATE ${LIBRT})
     endif()
     if(LIBSOCKET)
-        target_link_libraries(dbus-1 ${LIBSOCKET})
+        target_link_libraries(dbus-1 PRIVATE ${LIBSOCKET})
     endif()
     if (HAVE_BACKTRACE)
-        target_link_libraries(dbus-1 ${Backtrace_LIBRARY})
+        target_link_libraries(dbus-1 PRIVATE ${Backtrace_LIBRARY})
         target_include_directories(dbus-1 PRIVATE ${Backtrace_INCLUDE_DIR})
     endif()
+    if(HAVE_LTTNG)
+        add_lttng_tracepoint(dbus-1 dbus-lttng-verbose.tp)
+        target_compile_definitions(dbus-1 PRIVATE HAVE_LTTNG)
+        target_include_directories(dbus-1 PRIVATE ${LTTNG_INCLUDE_DIR} ${CMAKE_CURRENT_BINARY_DIR})
+        target_link_libraries(dbus-1 PRIVATE ${LTTNG_LIBRARIES})
+    endif()
 endif()
 
 # target definitions passed to the clients

dbus/dbus-internals.c

@@ -37,6 +37,8 @@
 #ifdef DBUS_USE_OUTPUT_DEBUG_STRING
 #include <windows.h>
 #include <mbstring.h>
+#elif defined(HAVE_LTTNG)
+#include "dbus-lttng-verbose-tp.h"
 #endif
 
 /**
@@ -467,7 +469,7 @@ _dbus_verbose_real (
   if (!_dbus_is_verbose_real())
     return;
 
-#ifndef DBUS_USE_OUTPUT_DEBUG_STRING
+#if !defined(DBUS_USE_OUTPUT_DEBUG_STRING) && !defined(HAVE_LTTNG)
   /* Print out pid before the line */
   if (need_pid)
     {
@@ -517,6 +519,25 @@ out:
       }
     _dbus_string_free (&out);
   }
+#elif defined(HAVE_LTTNG)
+  {
+    DBusString out = _DBUS_STRING_INIT_INVALID;
+    const char *message = NULL;
+
+    if (!_dbus_string_init (&out))
+      goto out;
+
+#ifdef DBUS_CPP_SUPPORTS_VARIABLE_MACRO_ARGUMENTS
+    if (!_dbus_string_append_printf (&out, "[%s(%d):%s] ", _dbus_file_path_extract_elements_from_tail (file, 2), line, function))
+      goto out;
+#endif
+    if (!_dbus_string_append_printf_valist (&out, format, args))
+      goto out;
+    message = _dbus_string_get_const_data (&out);
+out:
+    tracepoint(dbus, verbose, message ? message : "Out of memory while formatting verbose message");
+    _dbus_string_free (&out);
+  }
 #else
 #ifdef DBUS_CPP_SUPPORTS_VARIABLE_MACRO_ARGUMENTS
   fprintf (stderr, "[%s(%d):%s] ",_dbus_file_path_extract_elements_from_tail(file,2),line,function);

dbus/dbus-lttng-verbose.tp

@@ -0,0 +1,10 @@
+TRACEPOINT_EVENT(
+    dbus,
+    verbose,
+    TP_ARGS(
+        const char*, my_string_arg
+    ),
+    TP_FIELDS(
+        ctf_string(my_string_field, my_string_arg)
+    )
+)

test/CMakeLists.txt

@@ -74,6 +74,10 @@ set(manual-paths_SOURCES
     manual-paths.c
 )
 
+if(HAVE_LTTNG)
+    add_test_executable(test-lttng test-lttng.c dbus-testutils ${LTTNG_LIBRARIES})
+    add_lttng_tracepoint(test-lttng test-lttng.tp)
+endif()
 add_helper_executable(manual-dir-iter ${manual-dir-iter_SOURCES} ${DBUS_INTERNAL_LIBRARIES})
 add_helper_executable(test-service ${test-service_SOURCES} dbus-testutils)
 add_helper_executable(test-names ${test-names_SOURCES} dbus-testutils)

test/test-lttng.c

@@ -0,0 +1,12 @@
+
+
+#include <lttng/tracef.h>
+
+#include "test-lttng-tp.h"
+
+int main(int argc, char **argv)
+{
+      tracef("argc %d, argv[0] %s", argc, argv[0]);
+      tracepoint(dbus, lttng_test, argc, argv[0]);
+      return 0;
+}

test/test-lttng.tp

@@ -0,0 +1,12 @@
+TRACEPOINT_EVENT(
+    dbus,
+    lttng_test,
+    TP_ARGS(
+        int, my_integer_arg,
+        const char*, my_string_arg
+    ),
+    TP_FIELDS(
+        ctf_integer(int, my_integer_field, my_integer_arg)
+        ctf_string(my_string_field, my_string_arg)
+    )
+)