trace, lttng: require .pc files

The next version of lttng-libs will not require liburcu at run time anymore.
Therefore, it is expected that distros will not include the urcubp libraries
anymore when installing lttng-ust-devel.

To avoid future problems, just require pkg-config to detect lttng-ust.
The .pc files for lttng-ust correctly include liburcubp.a for static
builds, and have always done since pkg-config files were added in 2011.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 20210712155710.520889-1-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

configure

@@ -3606,21 +3606,8 @@ fi
 ##########################################
 # For 'ust' backend, test if ust headers are present
 if have_backend "ust"; then
-  cat > $TMPC << EOF
-#include <lttng/tracepoint.h>
-int main(void) { return 0; }
-EOF
-  if compile_prog "" "-Wl,--no-as-needed -ldl" ; then
-    if $pkg_config lttng-ust --exists; then
-      lttng_ust_libs=$($pkg_config --libs lttng-ust)
-    else
-      lttng_ust_libs="-llttng-ust -ldl"
-    fi
-    if $pkg_config liburcu-bp --exists; then
-      urcu_bp_libs=$($pkg_config --libs liburcu-bp)
-    else
-      urcu_bp_libs="-lurcu-bp"
-    fi
+  if $pkg_config lttng-ust --exists; then
+    lttng_ust_libs=$($pkg_config --libs lttng-ust)
   else
     error_exit "Trace backend 'ust' missing lttng-ust header files"
   fi
@@ -4773,7 +4760,6 @@ fi
 if have_backend "ust"; then
   echo "CONFIG_TRACE_UST=y" >> $config_host_mak
   echo "LTTNG_UST_LIBS=$lttng_ust_libs" >> $config_host_mak
-  echo "URCU_BP_LIBS=$urcu_bp_libs" >> $config_host_mak
 fi
 if have_backend "dtrace"; then
   echo "CONFIG_TRACE_DTRACE=y" >> $config_host_mak

meson.build

@@ -319,10 +319,6 @@ lttng = not_found
 if 'CONFIG_TRACE_UST' in config_host
   lttng = declare_dependency(link_args: config_host['LTTNG_UST_LIBS'].split())
 endif
-urcubp = not_found
-if 'CONFIG_TRACE_UST' in config_host
-  urcubp = declare_dependency(link_args: config_host['URCU_BP_LIBS'].split())
-endif
 pixman = not_found
 if have_system or have_tools
   pixman = dependency('pixman-1', required: have_system, version:'>=0.21.8',

trace/meson.build

@@ -26,7 +26,7 @@ foreach dir : [ '.' ] + trace_events_subdirs
                                 input: trace_events_file,
                                 command: [ tracetool, group, '--format=ust-events-h', '@INPUT@', '@OUTPUT@' ],
                                 depend_files: tracetool_depends)
-    trace_ss.add(trace_ust_h, lttng, urcubp)
+    trace_ss.add(trace_ust_h, lttng)
     genh += trace_ust_h
   endif
   trace_ss.add(trace_h, trace_c)