linux-kernel - [PATCH v2 7/7] perf hwmon_pmu: Switch event discovery to io_dir_

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Message-Id: <20250207232452.994822-8-irogers@google.com>
Date: Fri,  7 Feb 2025 15:24:48 -0800
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>, Sam James <sam@...too.org>, 
	Jesper Juhl <jesperjuhl76@...il.com>, James Clark <james.clark@...aro.org>, 
	Zhongqiu Han <quic_zhonhan@...cinc.com>, Yicong Yang <yangyicong@...ilicon.com>, 
	Thomas Richter <tmricht@...ux.ibm.com>, Michael Petlan <mpetlan@...hat.com>, 
	Veronika Molnarova <vmolnaro@...hat.com>, Anne Macedo <retpolanne@...teo.net>, 
	Dominique Martinet <asmadeus@...ewreck.org>, 
	Jean-Philippe Romain <jean-philippe.romain@...s.st.com>, Junhao He <hejunhao3@...wei.com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
	"Krzysztof Łopatowski" <krzysztof.m.lopatowski@...il.com>
Subject: [PATCH v2 7/7] perf hwmon_pmu: Switch event discovery to io_dir__readdir

Avoid DIR allocations when scanning sysfs by using io_dir for the
readdir implementation, that allocates about 1kb on the stack.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/hwmon_pmu.c | 42 +++++++++++++++----------------------
 1 file changed, 17 insertions(+), 25 deletions(-)

diff --git a/tools/perf/util/hwmon_pmu.c b/tools/perf/util/hwmon_pmu.c
index acd889b2462f..3cce77fc8004 100644
--- a/tools/perf/util/hwmon_pmu.c
+++ b/tools/perf/util/hwmon_pmu.c
@@ -11,13 +11,13 @@
 #include <sys/types.h>
 #include <assert.h>
 #include <ctype.h>
-#include <dirent.h>
 #include <fcntl.h>
 #include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
 #include <api/fs/fs.h>
 #include <api/io.h>
+#include <api/io_dir.h>
 #include <linux/kernel.h>
 #include <linux/string.h>
 #include <linux/zalloc.h>
@@ -235,31 +235,22 @@ static void fix_name(char *p)
 
 static int hwmon_pmu__read_events(struct hwmon_pmu *pmu)
 {
-	DIR *dir;
-	struct dirent *ent;
-	int dup_fd, err = 0;
+	int err = 0;
 	struct hashmap_entry *cur, *tmp;
 	size_t bkt;
+	struct io_dirent64 *ent;
+	struct io_dir dir;
 
 	if (pmu->pmu.sysfs_aliases_loaded)
 		return 0;
 
-	/*
-	 * Use a dup-ed fd as closedir will close it. Use openat so that the
-	 * directory contents are refreshed.
-	 */
-	dup_fd = openat(pmu->hwmon_dir_fd, ".", O_DIRECTORY);
+	/* Use openat so that the directory contents are refreshed. */
+	io_dir__init(&dir, openat(pmu->hwmon_dir_fd, ".", O_CLOEXEC | O_DIRECTORY | O_RDONLY));
 
-	if (dup_fd == -1)
-		return -ENOMEM;
+	if (dir.dirfd < 0)
+		return -ENOENT;
 
-	dir = fdopendir(dup_fd);
-	if (!dir) {
-		close(dup_fd);
-		return -ENOMEM;
-	}
-
-	while ((ent = readdir(dir)) != NULL) {
+	while ((ent = io_dir__readdir(&dir)) != NULL) {
 		enum hwmon_type type;
 		int number;
 		enum hwmon_item item;
@@ -347,7 +338,7 @@ static int hwmon_pmu__read_events(struct hwmon_pmu *pmu)
 	pmu->pmu.sysfs_aliases_loaded = true;
 
 err_out:
-	closedir(dir);
+	close(dir.dirfd);
 	return err;
 }
 
@@ -702,8 +693,8 @@ int hwmon_pmu__check_alias(struct parse_events_terms *terms, struct perf_pmu_inf
 int perf_pmus__read_hwmon_pmus(struct list_head *pmus)
 {
 	char *line = NULL;
-	DIR *class_hwmon_dir;
-	struct dirent *class_hwmon_ent;
+	struct io_dirent64 *class_hwmon_ent;
+	struct io_dir class_hwmon_dir;
 	char buf[PATH_MAX];
 	const char *sysfs = sysfs__mountpoint();
 
@@ -711,11 +702,12 @@ int perf_pmus__read_hwmon_pmus(struct list_head *pmus)
 		return 0;
 
 	scnprintf(buf, sizeof(buf), "%s/class/hwmon/", sysfs);
-	class_hwmon_dir = opendir(buf);
-	if (!class_hwmon_dir)
+	io_dir__init(&class_hwmon_dir, open(buf, O_CLOEXEC | O_DIRECTORY | O_RDONLY));
+
+	if (class_hwmon_dir.dirfd < 0)
 		return 0;
 
-	while ((class_hwmon_ent = readdir(class_hwmon_dir)) != NULL) {
+	while ((class_hwmon_ent = io_dir__readdir(&class_hwmon_dir)) != NULL) {
 		size_t line_len;
 		int hwmon_dir, name_fd;
 		struct io io;
@@ -745,7 +737,7 @@ int perf_pmus__read_hwmon_pmus(struct list_head *pmus)
 		close(name_fd);
 	}
 	free(line);
-	closedir(class_hwmon_dir);
+	close(class_hwmon_dir.dirfd);
 	return 0;
 }
 
-- 
2.48.1.502.g6dc24dfdaf-goog