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trace2: implement trace2_printf() for event target

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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 <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Josh Steadmon 2024-08-22 14:57:45 -07:00 committed by Junio C Hamano
parent 3a7362eb9f
commit cbe140754b
2 changed files with 35 additions and 4 deletions
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17
Documentation/technical/api-trace2.txt
View file

@ -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

22
trace2/tr2_tgt_event.c
View file

@ -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,
};