[PATCH 11/20] trace: don't emit TraceEvent structs when 'nop' backend is used

["Daniel P. Berrangé" <berrange@redhat.com>]

The 'nop' backend is a short-hand for no trace probe usage
at all. The emitted functions become a no-op, and as such
there is no need to emit the TraceEvent structs, nor the
DSTATE variables they reference.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 scripts/tracetool/format/c.py | 75 ++++++++++++++++++-----------------
 scripts/tracetool/format/h.py | 16 +++++---
 tests/tracetool/nop.c         | 29 --------------
 tests/tracetool/nop.h         |  6 +--
 4 files changed, 50 insertions(+), 76 deletions(-)

diff --git a/scripts/tracetool/format/c.py b/scripts/tracetool/format/c.py
index de1c154a881..5f6669c917c 100644
--- a/scripts/tracetool/format/c.py
+++ b/scripts/tracetool/format/c.py
@@ -29,41 +29,42 @@ def generate(events, backend, group):
         '#include "%s"' % header,
         '')
 
-    for e in events:
-        out('uint8_t %s;' % e.api(e.QEMU_DSTATE))
-
-    for e in events:
-        out('TraceEvent %(event)s = {',
-            '#ifdef CONFIG_TRACE_SIMPLE',
-            '    .id = 0,',
-            '#endif',
-            '    .name = \"%(name)s\",',
-            '    .sstate = %(sstate)s,',
-            '    .dstate = &%(dstate)s',
+    if len(list(backend.backend_modules())):
+        for e in events:
+            out('uint8_t %s;' % e.api(e.QEMU_DSTATE))
+
+        for e in events:
+            out('TraceEvent %(event)s = {',
+                '#ifdef CONFIG_TRACE_SIMPLE',
+                '    .id = 0,',
+                '#endif',
+                '    .name = \"%(name)s\",',
+                '    .sstate = %(sstate)s,',
+                '    .dstate = &%(dstate)s',
+                '};',
+                event = e.api(e.QEMU_EVENT),
+                name = e.name,
+                sstate = "TRACE_%s_ENABLED" % e.name.upper(),
+                dstate = e.api(e.QEMU_DSTATE))
+
+        out('TraceEvent *%(group)s_trace_events[] = {',
+            group = group.lower())
+
+        for e in events:
+            out('    &%(event)s,', event = e.api(e.QEMU_EVENT))
+
+        out('  NULL,',
             '};',
-            event = e.api(e.QEMU_EVENT),
-            name = e.name,
-            sstate = "TRACE_%s_ENABLED" % e.name.upper(),
-            dstate = e.api(e.QEMU_DSTATE))
-
-    out('TraceEvent *%(group)s_trace_events[] = {',
-        group = group.lower())
-
-    for e in events:
-        out('    &%(event)s,', event = e.api(e.QEMU_EVENT))
-
-    out('  NULL,',
-        '};',
-        '')
-
-    out('static void trace_%(group)s_register_events(void)',
-        '{',
-        '    trace_event_register_group(%(group)s_trace_events);',
-        '}',
-        'trace_init(trace_%(group)s_register_events)',
-        group = group.lower())
-
-    backend.generate_begin(active_events, group)
-    for event in active_events:
-        backend.generate(event, group)
-    backend.generate_end(active_events, group)
+            '')
+
+        out('static void trace_%(group)s_register_events(void)',
+            '{',
+            '    trace_event_register_group(%(group)s_trace_events);',
+            '}',
+            'trace_init(trace_%(group)s_register_events)',
+            group = group.lower())
+
+        backend.generate_begin(active_events, group)
+        for event in active_events:
+            backend.generate(event, group)
+        backend.generate_end(active_events, group)
diff --git a/scripts/tracetool/format/h.py b/scripts/tracetool/format/h.py
index 4dc1ad7eb15..6ffb7256e31 100644
--- a/scripts/tracetool/format/h.py
+++ b/scripts/tracetool/format/h.py
@@ -27,12 +27,16 @@ def generate(events, backend, group):
         '#include "%s"' % header,
         '')
 
-    for e in events:
-        out('extern TraceEvent %(event)s;',
-            event = e.api(e.QEMU_EVENT))
-
-    for e in events:
-        out('extern uint8_t %s;' % e.api(e.QEMU_DSTATE))
+    if len(list(backend.backend_modules())):
+        for e in events:
+            out('extern TraceEvent %(event)s;',
+                event = e.api(e.QEMU_EVENT))
+
+        for e in events:
+            out('extern uint8_t %s;' % e.api(e.QEMU_DSTATE))
+    else:
+        for e in events:
+            out('#define %s 0' % e.api(e.QEMU_DSTATE))
 
     # static state
     for e in events:
diff --git a/tests/tracetool/nop.c b/tests/tracetool/nop.c
index f83d06252ea..d34cc0ca742 100644
--- a/tests/tracetool/nop.c
+++ b/tests/tracetool/nop.c
@@ -5,32 +5,3 @@
 #include "qemu/module.h"
 #include "trace-testsuite.h"
 
-uint8_t _TRACE_TEST_BLAH_DSTATE;
-uint8_t _TRACE_TEST_WIBBLE_DSTATE;
-TraceEvent _TRACE_TEST_BLAH_EVENT = {
-#ifdef CONFIG_TRACE_SIMPLE
-    .id = 0,
-#endif
-    .name = "test_blah",
-    .sstate = TRACE_TEST_BLAH_ENABLED,
-    .dstate = &_TRACE_TEST_BLAH_DSTATE
-};
-TraceEvent _TRACE_TEST_WIBBLE_EVENT = {
-#ifdef CONFIG_TRACE_SIMPLE
-    .id = 0,
-#endif
-    .name = "test_wibble",
-    .sstate = TRACE_TEST_WIBBLE_ENABLED,
-    .dstate = &_TRACE_TEST_WIBBLE_DSTATE
-};
-TraceEvent *testsuite_trace_events[] = {
-    &_TRACE_TEST_BLAH_EVENT,
-    &_TRACE_TEST_WIBBLE_EVENT,
-  NULL,
-};
-
-static void trace_testsuite_register_events(void)
-{
-    trace_event_register_group(testsuite_trace_events);
-}
-trace_init(trace_testsuite_register_events)
diff --git a/tests/tracetool/nop.h b/tests/tracetool/nop.h
index 443f5e0cf6e..64b6b005684 100644
--- a/tests/tracetool/nop.h
+++ b/tests/tracetool/nop.h
@@ -6,10 +6,8 @@
 
 #include "trace/control.h"
 
-extern TraceEvent _TRACE_TEST_BLAH_EVENT;
-extern TraceEvent _TRACE_TEST_WIBBLE_EVENT;
-extern uint8_t _TRACE_TEST_BLAH_DSTATE;
-extern uint8_t _TRACE_TEST_WIBBLE_DSTATE;
+#define _TRACE_TEST_BLAH_DSTATE 0
+#define _TRACE_TEST_WIBBLE_DSTATE 0
 #define TRACE_TEST_BLAH_ENABLED 1
 #define TRACE_TEST_WIBBLE_ENABLED 1
 
-- 
2.55.0