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

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Message-ID: <Y6VKEfsGu0Pteb8e@leoy-yangtze.lan>
Date:   Fri, 23 Dec 2022 14:26:25 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     James Clark <james.clark@....com>
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 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.

Thanks,
Leo

> +}
> +
>  static int perf_pmu__new_caps(struct list_head *list, char *name, char *value)
>  {
>  	struct perf_pmu_caps *caps = zalloc(sizeof(*caps));
> diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
> index 8f39e2d17fb1..c1d138fe9602 100644
> --- a/tools/perf/util/pmu.h
> +++ b/tools/perf/util/pmu.h
> @@ -230,6 +230,8 @@ bool pmu_have_event(const char *pname, const char *name);
>  
>  int perf_pmu__scan_file(struct perf_pmu *pmu, const char *name, const char *fmt, ...) __scanf(3, 4);
>  
> +bool perf_pmu__file_exists(struct perf_pmu *pmu, const char *name);
> +
>  int perf_pmu__test(void);
>  
>  struct perf_event_attr *perf_pmu__get_default_config(struct perf_pmu *pmu);
> -- 
> 2.25.1
>