linux-kernel - [PATCH v1 1/2] perf hwmon_pmu: Use openat rather than dup to refresh directory

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Message-Id: <20241206042306.1055913-1-irogers@google.com>
Date: Thu,  5 Dec 2024 20:23:05 -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>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: [PATCH v1 1/2] perf hwmon_pmu: Use openat rather than dup to refresh directory

The hwmon PMU test will make a temp directory, open the directory with
O_DIRECTORY then fill it with contents. As the open is before the
filling the contents the later fdopendir may reflect the initial empty
state, meaning no events are seen. Change to re-open the directory,
rather than dup the fd, so the latest contents are seen.

Minor tweaks/additions to debug messages.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/hwmon_pmu.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/hwmon_pmu.c b/tools/perf/util/hwmon_pmu.c
index e61429b38ba7..4acb9bb19b84 100644
--- a/tools/perf/util/hwmon_pmu.c
+++ b/tools/perf/util/hwmon_pmu.c
@@ -258,8 +258,12 @@ static int hwmon_pmu__read_events(struct hwmon_pmu *pmu)
 	if (pmu->pmu.sysfs_aliases_loaded)
 		return 0;
 
-	/* Use a dup-ed fd as closedir will close it. */
-	dup_fd = dup(pmu->hwmon_dir_fd);
+	/*
+	 * 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);
+
 	if (dup_fd == -1)
 		return -ENOMEM;
 
@@ -336,6 +340,9 @@ static int hwmon_pmu__read_events(struct hwmon_pmu *pmu)
 			close(fd);
 		}
 	}
+	if (hashmap__size(&pmu->events) == 0)
+		pr_debug2("hwmon_pmu: %s has no events\n", pmu->pmu.name);
+
 	hashmap__for_each_entry_safe((&pmu->events), cur, tmp, bkt) {
 		union hwmon_pmu_event_key key = {
 			.type_and_num = cur->key,
@@ -343,8 +350,8 @@ static int hwmon_pmu__read_events(struct hwmon_pmu *pmu)
 		struct hwmon_pmu_event_value *value = cur->pvalue;
 
 		if (!test_bit(HWMON_ITEM_INPUT, value->items)) {
-			pr_debug("hwmon_pmu: removing event '%s%d' that has no input file\n",
-				hwmon_type_strs[key.type], key.num);
+			pr_debug("hwmon_pmu: %s removing event '%s%d' that has no input file\n",
+				pmu->pmu.name, hwmon_type_strs[key.type], key.num);
 			hashmap__delete(&pmu->events, key.type_and_num, &key, &value);
 			zfree(&value->label);
 			zfree(&value->name);
-- 
2.47.0.338.g60cca15819-goog