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tracing: Fix fully-qualified variable reference printing in histograms

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The syntax for fully-qualified variable references in histograms is
subsys.event.$var, which is parsed correctly, but not displayed correctly
when printing a histogram spec. The current code puts the $ reference at
the beginning of the fully-qualified variable name i.e. $subsys.event.var,
which is incorrect.

Before:

trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-$sched.sched_wakeup.ts0: ...

After:

trigger info: hist:keys=next_comm:vals=hitcount:wakeup_lat=common_timestamp.usecs-sched.sched_wakeup.$ts0: ...

Link: https://patch.msgid.link/5dee9a86d062a4dd68c2214f3d90ac93811e1951.1776112478.git.zanussi@kernel.org
Signed-off-by: Tom Zanussi <zanussi@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Tom Zanussi 2026-04-13 17:35:37 -05:00 committed by Steven Rostedt (Google)
parent fad217e16f
commit 9236eebd13
1 changed files with 10 additions and 5 deletions
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15
kernel/trace/trace_events_hist.c
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@ -1361,9 +1361,12 @@ static const char *hist_field_name(struct hist_field *field,
field->flags & HIST_FIELD_FL_VAR_REF) {
if (field->system) {
static char full_name[MAX_FILTER_STR_VAL];
static char *fmt;
int len;
len = snprintf(full_name, sizeof(full_name), "%s.%s.%s",
fmt = field->flags & HIST_FIELD_FL_VAR_REF ? "%s.%s.$%s" : "%s.%s.%s";
len = snprintf(full_name, sizeof(full_name), fmt,
field->system, field->event_name,
field->name);
if (len >= sizeof(full_name))
@ -1742,9 +1745,10 @@ static const char *get_hist_field_flags(struct hist_field *hist_field)
static void expr_field_str(struct hist_field *field, char *expr)
{
if (field->flags & HIST_FIELD_FL_VAR_REF)
strcat(expr, "$");
else if (field->flags & HIST_FIELD_FL_CONST) {
if (field->flags & HIST_FIELD_FL_VAR_REF) {
if (!field->system)
strcat(expr, "$");
} else if (field->flags & HIST_FIELD_FL_CONST) {
char str[HIST_CONST_DIGITS_MAX];
snprintf(str, HIST_CONST_DIGITS_MAX, "%llu", field->constant);
@ -6156,7 +6160,8 @@ static void hist_field_print(struct seq_file *m, struct hist_field *hist_field)
else if (field_name) {
if (hist_field->flags & HIST_FIELD_FL_VAR_REF ||
hist_field->flags & HIST_FIELD_FL_ALIAS)
seq_putc(m, '$');
if (!hist_field->system)
seq_putc(m, '$');
seq_printf(m, "%s", field_name);
} else if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP)
seq_puts(m, "common_timestamp");