linux-kernel - Re: [PATCH v2 1/4] perf trace: substitute CAP_SYS_ADMIN with CAP

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Date:   Thu, 23 Apr 2020 10:20:52 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH v2 1/4] perf trace: substitute CAP_SYS_ADMIN with
 CAP_PERFMON in error message

Em Wed, Apr 22, 2020 at 05:44:02PM +0300, Alexey Budankov escreveu:
> 
> Update error message to mention CAP_PERFMON only. CAP_SYS_ADMIN still
> works in keeping with user space backward compatibility approach.

This will confuse users that build the latest perf to use in older
systems where CAP_PERFMON isn't available, probably we need to, in these
cases, check for the existence of CAP_PERFMON to provide a better
warning message, something like:

  You need CAP_ADMIN or update your kernel and libcap to one that supports
  CAP_PERFMON.

For systems without CAP_PERFMON, while mentioning only CAP_PERFMON for
systems where it is present, right?
 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>  tools/perf/builtin-ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/perf/builtin-ftrace.c b/tools/perf/builtin-ftrace.c
> index 55eda54240fb..39d43ad02f30 100644
> --- a/tools/perf/builtin-ftrace.c
> +++ b/tools/perf/builtin-ftrace.c
> @@ -288,7 +288,7 @@ static int __cmd_ftrace(struct perf_ftrace *ftrace, int argc, const char **argv)
>  	      perf_cap__capable(CAP_SYS_ADMIN))) {
>  		pr_err("ftrace only works for %s!\n",
>  #ifdef HAVE_LIBCAP_SUPPORT
> -		"users with the CAP_PERFMON or CAP_SYS_ADMIN capability"
> +		"users with the CAP_PERFMON capability"
>  #else
>  		"root"
>  #endif
> -- 
> 2.24.1
> 

-- 

- Arnaldo