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@google.com>
Link: https://lore.kernel.org/r/20250222061015.303622-8-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

1 files 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;
 }