On Fri, Aug 22, 2025 at 02:26:44PM +0200, Paolo Bonzini wrote:
> This simplifies the Python code and reduces the size of the tracepoints.
>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> tests/tracetool/ftrace.h | 28 ++++++----------------------
> trace/ftrace.h | 1 +
> trace/ftrace.c | 15 +++++++++++++++
> scripts/tracetool/backend/ftrace.py | 12 ++----------
> 4 files changed, 24 insertions(+), 32 deletions(-)
>
> diff --git a/tests/tracetool/ftrace.h b/tests/tracetool/ftrace.h
> index fe22ea0f09f..1dfe4239413 100644
> --- a/tests/tracetool/ftrace.h
> +++ b/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 */
snip
> diff --git a/trace/ftrace.c b/trace/ftrace.c
> index 9749543d9b2..6875faedb9c 100644
> --- a/trace/ftrace.c
> +++ b/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);
You're just copying the existing code pattern which is fine for now so
Reviewed-by: Daniel P. Berrangé <berra...@redhat.com>
More generally though, IMHO, QEMU would be better off bringing in
gnulib's 'ignore_value' macro, but simplified since we don't care
about ancient GCC
#define ignore_value(x) \
(__extension__ ({ __typeof__ (x) __x = (x); (void) __x; }))
so that we don't need to play games with extra variables. eg
ignore_value(write(trace_marker_fd, ftrace_buf, trlen));
With regards,
Daniel
[1] https://github.com/coreutils/gnulib/blob/master/lib/ignore-value.h#L38
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