trace/ftrace: move snprintf+write from tracepoints to ftrace.c

This simplifies the Python code and reduces the size of the tracepoints.

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250929154938.594389-6-pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

scripts/tracetool/backend/ftrace.py

@@ -28,18 +28,10 @@ def generate_h(event, group):
     if len(event.args) > 0:
         argnames = ", " + argnames
 
-    out('    {',
-        '        char ftrace_buf[MAX_TRACE_STRLEN];',
-        '        int unused __attribute__ ((unused));',
-        '        int trlen;',
-        '        if (trace_event_get_state(%(event_id)s)) {',
+    out('    if (trace_event_get_state(%(event_id)s)) {',
         '#line %(event_lineno)d "%(event_filename)s"',
-        '            trlen = snprintf(ftrace_buf, MAX_TRACE_STRLEN,',
-        '                             "%(name)s " %(fmt)s "\\n" %(argnames)s);',
+        '        ftrace_write("%(name)s " %(fmt)s "\\n" %(argnames)s);',
         '#line %(out_next_lineno)d "%(out_filename)s"',
-        '            trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);',
-        '            unused = write(trace_marker_fd, ftrace_buf, trlen);',
-        '        }',
         '    }',
         name=event.name,
         args=event.args,

tests/tracetool/ftrace.h

@@ -21,18 +21,10 @@ extern uint16_t _TRACE_TEST_WIBBLE_DSTATE;
 
 static inline void trace_test_blah(void *context, const char *filename)
 {
-    {
-        char ftrace_buf[MAX_TRACE_STRLEN];
-        int unused __attribute__ ((unused));
-        int trlen;
-        if (trace_event_get_state(TRACE_TEST_BLAH)) {
+    if (trace_event_get_state(TRACE_TEST_BLAH)) {
 #line 4 "trace-events"
-            trlen = snprintf(ftrace_buf, MAX_TRACE_STRLEN,
-                             "test_blah " "Blah context=%p filename=%s" "\n" , context, filename);
-#line 33 "ftrace.h"
-            trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);
-            unused = write(trace_marker_fd, ftrace_buf, trlen);
-        }
+        ftrace_write("test_blah " "Blah context=%p filename=%s" "\n" , context, filename);
+#line 28 "ftrace.h"
     }
 }
 
@@ -42,18 +34,10 @@ static inline void trace_test_blah(void *context, const char *filename)
 
 static inline void trace_test_wibble(void *context, int value)
 {
-    {
-        char ftrace_buf[MAX_TRACE_STRLEN];
-        int unused __attribute__ ((unused));
-        int trlen;
-        if (trace_event_get_state(TRACE_TEST_WIBBLE)) {
+    if (trace_event_get_state(TRACE_TEST_WIBBLE)) {
 #line 5 "trace-events"
-            trlen = snprintf(ftrace_buf, MAX_TRACE_STRLEN,
-                             "test_wibble " "Wibble context=%p value=%d" "\n" , context, value);
-#line 54 "ftrace.h"
-            trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);
-            unused = write(trace_marker_fd, ftrace_buf, trlen);
-        }
+        ftrace_write("test_wibble " "Wibble context=%p value=%d" "\n" , context, value);
+#line 41 "ftrace.h"
     }
 }
 #endif /* TRACE_TESTSUITE_GENERATED_TRACERS_H */

trace/ftrace.c

@@ -38,6 +38,21 @@ static int find_mount(char *mount_point, const char *fstype)
     return ret;
 }
 
+void ftrace_write(const char *fmt, ...)
+{
+    char ftrace_buf[MAX_TRACE_STRLEN];
+    int unused __attribute__ ((unused));
+    int trlen;
+    va_list ap;
+
+    va_start(ap, fmt);
+    trlen = vsnprintf(ftrace_buf, MAX_TRACE_STRLEN, fmt, ap);
+    va_end(ap);
+
+    trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);
+    unused = write(trace_marker_fd, ftrace_buf, trlen);
+}
+
 bool ftrace_init(void)
 {
     char mount_point[PATH_MAX];

trace/ftrace.h

@@ -8,5 +8,6 @@
 extern int trace_marker_fd;
 
 bool ftrace_init(void);
+G_GNUC_PRINTF(1, 2) void ftrace_write(const char *fmt, ...);
 
 #endif /* TRACE_FTRACE_H */