[PATCH 2/2] libtracefs: Have end event variables not be the end event field name

From: Steven Rostedt
Date: Wed Aug 11 2021 - 20:55:51 EST


From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

Currently we have:

# sqlhist -n wakeup 'select end.next_pid, (end.TIMESTAMP - start.TIMESTAMP) as lat
from sched_waking as start join sched_switch as end on start.pid = end.next_pid'

produces:

echo 'wakeup s32 next_pid; u64 lat;' > /sys/kernel/tracing/synthetic_events
echo 'hist:keys=pid:__arg_18871_1=common_timestamp' > /sys/kernel/tracing/events/sched/sched_waking/trigger
echo 'hist:keys=next_pid:next_pid=next_pid,lat=common_timestamp-$__arg_18871_1:onmatch(sched.sched_waking).trace(wakeup,$next_pid,$lat)' > /sys/kernel/tracing/events/sched/sched_switch/trigger

The issue is that we have "next_pid=next_pid" where if we want to change
the above to use the "save" action:

hist:keys=next_pid:next_pid=next_pid,lat=common_timestamp-$__arg_18871_1:onmax($lat).save(next_pid)

It fails with:

hist:sched:sched_switch: error: Couldn't find field
Command: hist:keys=next_pid:next_pid=next_pid,lat=common_timestamp-$__arg_18871_1:onmax($lat).save(next_pid)
^

But by having the end vars be unique, then the above "save" works.

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
src/tracefs-hist.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/tracefs-hist.c b/src/tracefs-hist.c
index 8783ef4364bd..1e6bde7880f2 100644
--- a/src/tracefs-hist.c
+++ b/src/tracefs-hist.c
@@ -851,16 +851,19 @@ struct tracefs_synth *tracefs_synth_init(struct tep_handle *tep,

static int add_synth_fields(struct tracefs_synth *synth,
const struct tep_format_field *field,
- const char *name)
+ const char *name, const char *var)
{
char **list;
char *str;
int ret;

- str = add_synth_field(field, name);
+ str = add_synth_field(field, name ? : field->name);
if (!str)
return -1;

+ if (!name)
+ name = var;
+
list = tracefs_list_add(synth->synthetic_fields, str);
free(str);
if (!list)
@@ -942,7 +945,7 @@ int tracefs_synth_add_match_field(struct tracefs_synth *synth,
if (ret < 0)
goto pop_lists;

- ret = add_synth_fields(synth, key_field, name);
+ ret = add_synth_fields(synth, key_field, name, NULL);
if (ret < 0)
goto pop_lists;

@@ -1061,7 +1064,7 @@ int tracefs_synth_add_compare_field(struct tracefs_synth *synth,
if (ret < 0)
goto out_free;

- ret = add_synth_fields(synth, start_field, name);
+ ret = add_synth_fields(synth, start_field, name, NULL);
if (ret < 0)
goto out_free;

@@ -1106,7 +1109,7 @@ __hidden int synth_add_start_field(struct tracefs_synth *synth,
if (ret)
goto out_free;

- ret = add_synth_fields(synth, field, name);
+ ret = add_synth_fields(synth, field, name, NULL);
if (ret)
goto out_free;

@@ -1178,6 +1181,7 @@ int tracefs_synth_add_end_field(struct tracefs_synth *synth,
const char *name)
{
const struct tep_format_field *field;
+ char *tmp_var = NULL;
int ret;

if (!synth || !end_field) {
@@ -1186,17 +1190,17 @@ int tracefs_synth_add_end_field(struct tracefs_synth *synth,
}

if (!name)
- name = end_field;
+ tmp_var = new_arg(synth);

if (!trace_verify_event_field(synth->end_event, end_field, &field))
return -1;

- ret = add_var(&synth->end_vars, name, end_field, false);
+ ret = add_var(&synth->end_vars, name ? : tmp_var, end_field, false);
if (ret)
goto out;

- ret = add_synth_fields(synth, field, name);
-
+ ret = add_synth_fields(synth, field, name, tmp_var);
+ free(tmp_var);
out:
return ret;
}
--
2.30.2