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

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

[Paolo Bonzini]

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

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tests/tracetool/ftrace.h            | 26 ++++----------------------
 trace/ftrace.h                      |  1 +
 trace/ftrace.c                      | 13 +++++++++++++
 scripts/tracetool/backend/ftrace.py | 13 ++-----------
 4 files changed, 20 insertions(+), 33 deletions(-)

diff --git a/tests/tracetool/ftrace.h b/tests/tracetool/ftrace.h
index aa8d720a922..83e4adeed4d 100644
--- a/tests/tracetool/ftrace.h
+++ b/tests/tracetool/ftrace.h
@@ -21,18 +21,9 @@ 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 "[stdout]"
-            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);
     }
 }
 
@@ -42,18 +33,9 @@ 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 "[stdout]"
-            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);
     }
 }
 #endif /* TRACE_TESTSUITE_GENERATED_TRACERS_H */
diff --git a/trace/ftrace.h b/trace/ftrace.h
index cb5e35d2171..16c122816d1 100644
--- a/trace/ftrace.h
+++ b/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 */
diff --git a/trace/ftrace.c b/trace/ftrace.c
index 9749543d9b2..1d7e1ee6f6d 100644
--- a/trace/ftrace.c
+++ b/trace/ftrace.c
@@ -38,6 +38,19 @@ 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);
+    trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);
+    unused = write(trace_marker_fd, ftrace_buf, trlen);
+}
+
 bool ftrace_init(void)
 {
     char mount_point[PATH_MAX];
diff --git a/scripts/tracetool/backend/ftrace.py b/scripts/tracetool/backend/ftrace.py
index 5fa30ccc08e..1a96231dbab 100644
--- a/scripts/tracetool/backend/ftrace.py
+++ b/scripts/tracetool/backend/ftrace.py
@@ -28,18 +28,9 @@ 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);',
-        '#line %(out_next_lineno)d "%(out_filename)s"',
-        '            trlen = MIN(trlen, MAX_TRACE_STRLEN - 1);',
-        '            unused = write(trace_marker_fd, ftrace_buf, trlen);',
-        '        }',
+        '        ftrace_write("%(name)s " %(fmt)s "\\n" %(argnames)s);',
         '    }',
         name=event.name,
         args=event.args,
-- 
2.50.1

Re: [PATCH] trace/ftrace: move snprintf+write from tracepoints to ftrace.c

[Daniel P. Berrangé]

On Fri, Aug 08, 2025 at 11:11:10AM +0200, Paolo Bonzini wrote:
> This simplifies the Python code and reduces the size of the tracepoints.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  tests/tracetool/ftrace.h            | 26 ++++----------------------
>  trace/ftrace.h                      |  1 +
>  trace/ftrace.c                      | 13 +++++++++++++
>  scripts/tracetool/backend/ftrace.py | 13 ++-----------
>  4 files changed, 20 insertions(+), 33 deletions(-)


> diff --git a/trace/ftrace.c b/trace/ftrace.c
> index 9749543d9b2..1d7e1ee6f6d 100644
> --- a/trace/ftrace.c
> +++ b/trace/ftrace.c
> @@ -38,6 +38,19 @@ 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];

With regards,
Daniel
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