linux-kernel - Re: [PATCH v2 4/7] perf pmu: Add function to check if a pmu file exists

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Message-ID: <150442e1-4717-2b18-8f7d-febbd95ae570@arm.com>
Date:   Tue, 3 Jan 2023 16:22:11 +0000
From:   James Clark <james.clark@....com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     linux-perf-users@...r.kernel.org, tanmay@...vell.com,
        sgoutham@...vell.com, gcherian@...vell.com, lcherian@...vell.com,
        bbhushan2@...vell.com, German Gomez <german.gomez@....com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] perf pmu: Add function to check if a pmu file
 exists



On 23/12/2022 06:26, Leo Yan wrote:
> On Thu, Dec 22, 2022 at 04:03:24PM +0000, James Clark wrote:
>> From: German Gomez <german.gomez@....com>
>>
>> Add a utility function perf_pmu__file_exists() to check if a given pmu
>> file exists in the sysfs filesystem.
>>
>> Signed-off-by: German Gomez <german.gomez@....com>
>> Signed-off-by: James Clark <james.clark@....com>
>> ---
>>  tools/perf/util/pmu.c | 14 ++++++++++++++
>>  tools/perf/util/pmu.h |  2 ++
>>  2 files changed, 16 insertions(+)
>>
>> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
>> index 15b852b3c401..b72b2d892949 100644
>> --- a/tools/perf/util/pmu.c
>> +++ b/tools/perf/util/pmu.c
>> @@ -1739,6 +1739,20 @@ int perf_pmu__scan_file(struct perf_pmu *pmu, const char *name, const char *fmt,
>>  	return ret;
>>  }
>>  
>> +bool perf_pmu__file_exists(struct perf_pmu *pmu, const char *name)
>> +{
>> +	char path[PATH_MAX];
>> +	struct stat statbuf;
>> +
>> +	if (!perf_pmu__pathname_scnprintf(path, PATH_MAX, pmu->name, name))
>> +		return false;
>> +
>> +	if (!file_available(path))
>> +		return false;
>> +
>> +	return stat(path, &statbuf) == 0;
> 
> Can we simply return the returned value from file_available() and skip
> calling stat()?  Because file_available() invokes access() to detect if
> a file is existed or not, so here calling stat() is redundant.
> 

Yep that works. Fixed in V3.