linux-kernel - Re: [PATCH v2 2/7] perf: Use perf_pmu__open_file() and perf_pmu__scan

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Message-ID: <Y6Unt0E4qM5oqE9+@leoy-yangtze.lan>
Date:   Fri, 23 Dec 2022 11:59:51 +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,
        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 2/7] perf: Use perf_pmu__open_file() and
 perf_pmu__scan_file()

On Fri, Dec 23, 2022 at 11:45:21AM +0800, Leo Yan wrote:

[...]

> > @@ -103,8 +103,9 @@ static int test__perf_evsel__roundtrip_name_test(struct test_suite *test __maybe
> >  						 int subtest __maybe_unused)
> >  {
> >  	int err = 0, ret = 0;
> > +	char cpu_atom[] = "cpu_atom";
> >  
> > -	if (perf_pmu__has_hybrid() && perf_pmu__hybrid_mounted("cpu_atom"))
> > +	if (perf_pmu__has_hybrid() && perf_pmu__hybrid_mounted(cpu_atom))
> 
> After change the parameter 'name' to non const type in function
> perf_pmu__hybrid_mounted(), at here we still can pass string "cpu_atom"
> without warning, right?  If so, we don't need to define a local
> variable 'cpu_atom'.

Correct for above statement, I did experiment and confirmed building
failure after change the parameter to non const type and directly pass
string "cpu_atom":

tests/evsel-roundtrip-name.c: In function ‘test__perf_evsel__roundtrip_name_test’:
tests/evsel-roundtrip-name.c:108:64: error: passing argument 1 of ‘perf_pmu__hybrid_mounted’ discards ‘const’ qualifier from pointer target type [-Werror=discarded-qualifiers]
  108 |         if (perf_pmu__has_hybrid() && perf_pmu__hybrid_mounted("cpu_atom"))
      |                                                                ^~~~~~~~~~

But I still suggest we can keep const type for the parameter for
perf_pmu__hybrid_mounted(), this is more friendly for its callers
without define local strings.

Thanks,
Leo