[PATCH v2 1/3] trace2: implement trace2_printf() for event target
From: Josh Steadmon <hidden>
Date: 2024-08-22 21:57:52
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
The trace2 event target does not have an implementation for trace2_printf(). While the event target is for structured events, and trace2_printf() is for unstructured, human-readable messages, it may still be useful to wrap these unstructured messages in a structured JSON object. Among other things, it may reduce confusion when manually debugging using event trace data. Add a simple implementation for the event target that wraps trace2_printf() messages in a minimal JSON object. Document this in Documentation/technical/api-trace2.txt, and bump the event format version since we're adding a new event type. Signed-off-by: Josh Steadmon <redacted> --- Documentation/technical/api-trace2.txt | 17 +++++++++++++++-- trace2/tr2_tgt_event.c | 22 ++++++++++++++++++++-- 2 files changed, 35 insertions(+), 4 deletions(-)
diff --git a/Documentation/technical/api-trace2.txt b/Documentation/technical/api-trace2.txt
index de5fc25059..5817b18310 100644
--- a/Documentation/technical/api-trace2.txt
+++ b/Documentation/technical/api-trace2.txt@@ -128,7 +128,7 @@ yields ------------ $ cat ~/log.event -{"event":"version","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"3","exe":"2.20.1.155.g426c96fcdb"} +{"event":"version","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"4","exe":"2.20.1.155.g426c96fcdb"} {"event":"start","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621027Z","file":"common-main.c","line":39,"t_abs":0.001173,"argv":["git","version"]} {"event":"cmd_name","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621122Z","file":"git.c","line":432,"name":"version","hierarchy":"version"} {"event":"exit","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621236Z","file":"git.c","line":662,"t_abs":0.001227,"code":0}
@@ -344,7 +344,7 @@ only present on the "start" and "atexit" events. { "event":"version", ... - "evt":"3", # EVENT format version + "evt":"4", # EVENT format version "exe":"2.20.1.155.g426c96fcdb" # git version } ------------
@@ -835,6 +835,19 @@ The "value" field may be an integer or a string. } ------------ +`"printf"`:: + This event logs a human-readable message with no particular formatting + guidelines. ++ +------------ +{ + "event":"printf", + ... + "t_abs":0.015905, # elapsed time in seconds + "msg":"Hello world" # optional +} +------------ + == Example Trace2 API Usage
diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
index 59910a1a4f..45b0850a5e 100644
--- a/trace2/tr2_tgt_event.c
+++ b/trace2/tr2_tgt_event.c@@ -24,7 +24,7 @@ static struct tr2_dst tr2dst_event = { * a new field to an existing event, do not require an increment to the EVENT * format version. */ -#define TR2_EVENT_VERSION "3" +#define TR2_EVENT_VERSION "4" /* * Region nesting limit for messages written to the event target.
@@ -622,6 +622,24 @@ static void fn_data_json_fl(const char *file, int line, } } +static void fn_printf_va_fl(const char *file, int line, + uint64_t us_elapsed_absolute, + const char *fmt, va_list ap) +{ + const char *event_name = "printf"; + struct json_writer jw = JSON_WRITER_INIT; + double t_abs = (double)us_elapsed_absolute / 1000000.0; + + jw_object_begin(&jw, 0); + event_fmt_prepare(event_name, file, line, NULL, &jw); + jw_object_double(&jw, "t_abs", 6, t_abs); + maybe_add_string_va(&jw, "msg", fmt, ap); + jw_end(&jw); + + tr2_dst_write_line(&tr2dst_event, &jw.json); + jw_release(&jw); +} + static void fn_timer(const struct tr2_timer_metadata *meta, const struct tr2_timer *timer, int is_final_data)
@@ -694,7 +712,7 @@ struct tr2_tgt tr2_tgt_event = { .pfn_region_leave_printf_va_fl = fn_region_leave_printf_va_fl, .pfn_data_fl = fn_data_fl, .pfn_data_json_fl = fn_data_json_fl, - .pfn_printf_va_fl = NULL, + .pfn_printf_va_fl = fn_printf_va_fl, .pfn_timer = fn_timer, .pfn_counter = fn_counter, };
--
2.46.0.295.g3b9ea8a38a-goog