linux-kernel - [PATCH v1] perf tracepoint: Don't scan all tracepoints to test if one exists

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Date: Wed,  8 May 2024 23:05:41 -0700
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kan Liang <kan.liang@...ux.intel.com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf tracepoint: Don't scan all tracepoints to test if one exists

In is_valid_tracepoint, rather than scanning
"/sys/kernel/tracing/events/*/*" skipping any path where
"/sys/kernel/tracing/events/*/*/id" doesn't exist, and then testing if
"*:*" matches the tracepoint name, just use the given tracepoint name
replace the ':' with '/' and see if the id file exists. This turns a
nested directory search into a single file available test.

Rather than return 1 for valid and 0 for invalid, return true and
false.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/tracepoint.c | 53 ++++++++++++++----------------------
 tools/perf/util/tracepoint.h |  3 +-
 2 files changed, 23 insertions(+), 33 deletions(-)

diff --git a/tools/perf/util/tracepoint.c b/tools/perf/util/tracepoint.c
index 92dd8b455b90..cca6808f7951 100644
--- a/tools/perf/util/tracepoint.c
+++ b/tools/perf/util/tracepoint.c
@@ -4,10 +4,12 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <sys/param.h>
 #include <unistd.h>
 
 #include <api/fs/tracing_path.h>
+#include "fncache.h"
 
 int tp_event_has_id(const char *dir_path, struct dirent *evt_dir)
 {
@@ -26,39 +28,26 @@ int tp_event_has_id(const char *dir_path, struct dirent *evt_dir)
 /*
  * Check whether event is in <debugfs_mount_point>/tracing/events
  */
-int is_valid_tracepoint(const char *event_string)
+bool is_valid_tracepoint(const char *event_string)
 {
-	DIR *sys_dir, *evt_dir;
-	struct dirent *sys_dirent, *evt_dirent;
-	char evt_path[MAXPATHLEN];
-	char *dir_path;
-
-	sys_dir = tracing_events__opendir();
-	if (!sys_dir)
-		return 0;
+	char *dst, *path = malloc(strlen(event_string) + 4); /* Space for "/id\0". */
+	const char *src;
+	bool have_file;
 
-	for_each_subsystem(sys_dir, sys_dirent) {
-		dir_path = get_events_file(sys_dirent->d_name);
-		if (!dir_path)
-			continue;
-		evt_dir = opendir(dir_path);
-		if (!evt_dir)
-			goto next;
-
-		for_each_event(dir_path, evt_dir, evt_dirent) {
-			snprintf(evt_path, MAXPATHLEN, "%s:%s",
-				 sys_dirent->d_name, evt_dirent->d_name);
-			if (!strcmp(evt_path, event_string)) {
-				closedir(evt_dir);
-				put_events_file(dir_path);
-				closedir(sys_dir);
-				return 1;
-			}
-		}
-		closedir(evt_dir);
-next:
-		put_events_file(dir_path);
+	if (!path) {
+		/* Conservatively return false if memory allocation failed. */
+		return false;
 	}
-	closedir(sys_dir);
-	return 0;
+	/* Copy event_string replacing the ':' with '/'. */
+	for (src = event_string, dst = path; *src; src++, dst++)
+		*dst = (*src == ':') ? '/' : *src;
+	/* Add "/id\0". */
+	memcpy(dst, "/id", 4);
+
+	dst = get_events_file(path);
+	if (dst)
+		have_file = file_available(dst);
+	free(dst);
+	free(path);
+	return have_file;
 }
diff --git a/tools/perf/util/tracepoint.h b/tools/perf/util/tracepoint.h
index c4a110fe87d7..65ccb01fc312 100644
--- a/tools/perf/util/tracepoint.h
+++ b/tools/perf/util/tracepoint.h
@@ -4,6 +4,7 @@
 
 #include <dirent.h>
 #include <string.h>
+#include <stdbool.h>
 
 int tp_event_has_id(const char *dir_path, struct dirent *evt_dir);
 
@@ -20,6 +21,6 @@ int tp_event_has_id(const char *dir_path, struct dirent *evt_dir);
 		    (strcmp(sys_dirent->d_name, ".")) &&	\
 		    (strcmp(sys_dirent->d_name, "..")))
 
-int is_valid_tracepoint(const char *event_string);
+bool is_valid_tracepoint(const char *event_string);
 
 #endif /* __PERF_TRACEPOINT_H */
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog