Currently the tracing 'log' back emits special code to add timestamps
to trace points sent via qemu_log(). This current impl is a bad design
for a number of reasons.
* It changes the QEMU headers, such that 'error-report.h' content
is visible to all files using tracing, but only when the 'log'
backend is enabled. This has led to build failure bugs as devs
rarely test without the (default) 'log' backend enabled, and
CI can't cover every scenario for every trace backend.
* It bloats the trace points definitions which are inlined into
every probe location due to repeated inlining of timestamp
formatting code, adding MBs of overhead to QEMU.
* The tracing subsystem should not be treated any differently
from other users of qemu_log. They all would benefit from
having timestamps present.
* The timestamp emitted with the tracepoints is in a needlessly
different format to that used by error_report() in response
to '-msg timestamp=on'.
This fixes all these issues simply by moving timestamp formatting
into qemu_log, using the same approach as for error_report.
The code before:
static inline void _nocheck__trace_qcrypto_tls_creds_get_path(void * creds,
const char * filename, const char * path)
{
if (trace_event_get_state(TRACE_QCRYPTO_TLS_CREDS_GET_PATH) &&
qemu_loglevel_mask(LOG_TRACE)) {
if (message_with_timestamp) {
struct timeval _now;
gettimeofday(&_now, NULL);
qemu_log("%d@%zu.%06zu:qcrypto_tls_creds_get_path " "TLS creds
path creds=%p filename=%s path=%s" "\n",
qemu_get_thread_id(),
(size_t)_now.tv_sec, (size_t)_now.tv_usec
, creds, filename, path);
} else {
qemu_log("qcrypto_tls_creds_get_path " "TLS creds path creds=%p
filename=%s path=%s" "\n", creds, filename, path);
}
}
}
and after:
static inline void _nocheck__trace_qcrypto_tls_creds_get_path(void * creds,
const char * filename, const char * path)
{
if (trace_event_get_state(TRACE_QCRYPTO_TLS_CREDS_GET_PATH) &&
qemu_loglevel_mask(LOG_TRACE)) {
qemu_log("qcrypto_tls_creds_get_path " "TLS creds path creds=%p
filename=%s path=%s" "\n", creds, filename, path);
}
}
The log and error messages before:
$ qemu-system-x86_64 -trace qcrypto* -object
tls-creds-x509,id=tls0,dir=$HOME/tls -msg timestamp=on
2986097@1753122905.917608:qcrypto_tls_creds_x509_load TLS creds x509 load
creds=0x55d925bd9490 dir=/var/home/berrange/tls
2986097@1753122905.917621:qcrypto_tls_creds_get_path TLS creds path
creds=0x55d925bd9490 filename=ca-cert.pem path=<none>
2025-07-21T18:35:05.917626Z qemu-system-x86_64: Unable to access credentials
/var/home/berrange/tls/ca-cert.pem: No such file or directory
and after:
$ qemu-system-x86_64 -trace qcrypto* -object
tls-creds-x509,id=tls0,dir=$HOME/tls -msg timestamp=on
2025-07-21T18:43:28.089797Z qcrypto_tls_creds_x509_load TLS creds x509 load
creds=0x55bf5bf12380 dir=/var/home/berrange/tls
2025-07-21T18:43:28.089815Z qcrypto_tls_creds_get_path TLS creds path
creds=0x55bf5bf12380 filename=ca-cert.pem path=<none>
2025-07-21T18:43:28.089819Z qemu-system-x86_64: Unable to access credentials
/var/home/berrange/tls/ca-cert.pem: No such file or directory
The binary size before:
$ ls -alh qemu-system-x86_64
-rwxr-xr-x. 1 berrange berrange 87M Jul 21 19:39 qemu-system-x86_64
$ strip qemu-system-x86_64
$ ls -alh qemu-system-x86_64
-rwxr-xr-x. 1 berrange berrange 30M Jul 21 19:39 qemu-system-x86_64
and after:
$ ls -alh qemu-system-x86_64
-rwxr-xr-x. 1 berrange berrange 85M Jul 21 19:41 qemu-system-x86_64
$ strip qemu-system-x86_64
$ ls -alh qemu-system-x86_64
-rwxr-xr-x. 1 berrange berrange 29M Jul 21 19:41 qemu-system-x86_64
Signed-off-by: Daniel P. Berrangé <berra...@redhat.com>
---
scripts/tracetool/backend/log.py | 14 +-------------
util/log.c | 20 +++++++++++++++++++-
2 files changed, 20 insertions(+), 14 deletions(-)
diff --git a/scripts/tracetool/backend/log.py b/scripts/tracetool/backend/log.py
index 17ba1cd90e..bd6739ae41 100644
--- a/scripts/tracetool/backend/log.py
+++ b/scripts/tracetool/backend/log.py
@@ -20,7 +20,6 @@
def generate_h_begin(events, group):
out('#include "qemu/log-for-trace.h"',
- '#include "qemu/error-report.h"',
'')
@@ -36,20 +35,9 @@ def generate_h(event, group):
cond = "trace_event_get_state(%s)" % ("TRACE_" + event.name.upper())
out(' if (%(cond)s && qemu_loglevel_mask(LOG_TRACE)) {',
- ' if (message_with_timestamp) {',
- ' struct timeval _now;',
- ' gettimeofday(&_now, NULL);',
'#line %(event_lineno)d "%(event_filename)s"',
- ' qemu_log("%%d@%%zu.%%06zu:%(name)s " %(fmt)s "\\n",',
- ' qemu_get_thread_id(),',
- ' (size_t)_now.tv_sec, (size_t)_now.tv_usec',
- ' %(argnames)s);',
+ ' qemu_log("%(name)s " %(fmt)s "\\n"%(argnames)s);',
'#line %(out_next_lineno)d "%(out_filename)s"',
- ' } else {',
- '#line %(event_lineno)d "%(event_filename)s"',
- ' qemu_log("%(name)s " %(fmt)s "\\n"%(argnames)s);',
- '#line %(out_next_lineno)d "%(out_filename)s"',
- ' }',
' }',
cond=cond,
event_lineno=event.lineno,
diff --git a/util/log.c b/util/log.c
index 58d24de48a..abdcb6b311 100644
--- a/util/log.c
+++ b/util/log.c
@@ -145,10 +145,28 @@ void qemu_log_unlock(FILE *logfile)
void qemu_log(const char *fmt, ...)
{
- FILE *f = qemu_log_trylock();
+ FILE *f;
+ g_autofree const char *timestr = NULL;
+
+ /*
+ * Prepare the timestamp *outside* the logging
+ * lock so it better reflects when the message
+ * was emitted if we are delayed acquiring the
+ * mutex
+ */
+ if (message_with_timestamp) {
+ g_autoptr(GDateTime) dt = g_date_time_new_now_utc();
+ timestr = g_date_time_format_iso8601(dt);
+ }
+
+ f = qemu_log_trylock();
if (f) {
va_list ap;
+ if (timestr) {
+ fprintf(f, "%s ", timestr);
+ }
+
va_start(ap, fmt);
vfprintf(f, fmt, ap);
va_end(ap);
--
2.50.1
